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1. The southward migration of the Antarctic Circumpolar Current enhanced oceanic degassing of carbon dioxide during the last two deglaciations

Author

Xuyuan E. Ai, Lena M. Thöle, Alexandra Auderset, Mareike Schmitt, Simone Moretti, Anja S. Studer, Elisabeth Michel, Martin Wegmann, Alain Mazaud, Peter K. Bijl, Daniel M. Sigman, Alfredo Martínez-García, and Samuel L. Jaccard

Subjects
Geology, QE1-996.5, Environmental sciences, GE1-350
Abstract

Abstract Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial cycle, using biomarker-based reconstructions of surface layer temperature gradient in the southern Indian Ocean. The results show that the Antarctic Circumpolar Current was more equatorward during the ice ages and shifted ~6° poleward at the end of glacial terminations, consistent with Antarctic Circumpolar Current migration playing a role in glacial-interglacial atmospheric carbon dioxide change. Comparing the temporal evolution of the Antarctic Circumpolar Current mean latitude with other observations provides evidence that Earth’s axial tilt affects the strength and latitude range of Southern Ocean wind-driven upwelling, which may explain previously noted deviations in atmospheric carbon dioxide concentration from a simple correlation with Antarctic climate.

Published
2024
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2. Glacial heterogeneity in Southern Ocean carbon storage abated by fast South Indian deglacial carbon release

Author

Julia Gottschalk, Elisabeth Michel, Lena M. Thöle, Anja S. Studer, Adam P. Hasenfratz, Nicole Schmid, Martin Butzin, Alain Mazaud, Alfredo Martínez-García, Sönke Szidat, and Samuel L. Jaccard

Subjects
Science
Abstract

A Southern Ocean influences on the carbon cycle is considered a key component of deglacial changes. Here, the authors show spatial differences in glacial Southern Ocean carbon storage that dissipated rapidly 14.6 kyr ago, revealing a South Indian Ocean contribution to rapid deglacial atmospheric CO2 increases.

Published
2020
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3. The influence of high‐latitude flux lobes on the Holocene paleomagnetic record of IODP Site U1305 and the northern North Atlantic

Author

Joseph S. Stoner, James E. T. Channell, Alain Mazaud, Sarah E. Strano, and Chuang Xuan

Subjects
paleomagnetism, North Atlantic, paleointensity, Geophysics. Cosmic physics, QC801-809, Geology, QE1-996.5
Abstract

Paleomagnetic analysis and radiocarbon dating of an expanded Holocene deep‐sea sediment sequence recovered by Integrated Ocean Drilling Program (IODP) Expedition 303 from Labrador Sea Site U1305 (Lat.: 57°28.5 N, Long.: 48°31.8 W, water depth 3459 m) provides insights into mechanisms that drive both paleomagnetic secular variation (PSV) and magnetization acquisition in deep‐sea sediments. Seventeen radiocarbon dates on planktonic foraminifera define postglacial (ca. 8 ka) sedimentation rates as ranging from 35 to > 90 cm/kyr. Alternating field (AF) demagnetization of u‐channel samples show that these homogeneous sediments preserve a strong, stable, and consistently well‐defined component magnetization. Normalized remanence records pass reliability criteria for relative paleointensity (RPI) estimates. Assuming that the age of magnetization is most accurately defined by well dated PSV records with the highest sedimentation rates, allows us to estimate and correct for temporal offsets at Site U1305 interpreted to result from postdepositional remanence acquisition at a depth of ∼20 cm. Comparisons indicate that the northern North Atlantic PSV and RPI records are more consistent with European than North American records, and the evolution of virtual geomagnetic poles (VGP) are temporally and longitudinally similar to global reconstructions, though with much larger latitudinal variation. The largest deviations from a geocentric axial dipole (GAD) are observed during times of the highest intensities, in contrast to the usual assumption. These observations are consistent with the idea that PSV in the North Atlantic and elsewhere during the Holocene results from temporal oscillations of high‐latitude flux concentrations at a few recurrent locations.

Published
2013
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4. Antarctic Polar Front migrations in the Kerguelen Plateau region, Southern Ocean, over the past 360 kyrs

Author

Elisabeth Michel, Xavier Crosta, Takuya Itaki, Minoru Ikehara, Giuseppe Cortese, Olivier Ther, M. Civel-Mazens, Alain Mazaud, Kochi University, Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Climat et Magnétisme (CLIMAG), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
010504 meteorology & atmospheric sciences, 02 engineering and technology, Oceanography, 01 natural sciences, Kerguelen, Latitude, Water column, Fronts, 0202 electrical engineering, electronic engineering, information engineering, 14. Life underwater, Glacial period, Southern Ocean, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Trough (meteorology), ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Polar front, Diatoms, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Global and Planetary Change, geography, Plateau, geography.geographical_feature_category, Ocean current, 020206 networking & telecommunications, Radiolarians, 13. Climate action, Interglacial, Geology
Abstract

In the Southern Ocean (SO), climate-driven latitudinal migrations of the Antarctic Circumpolar Current (ACC) frontal system impact large-scale ocean circulation and primary productivity. Latitudinal migrations may not have been identical in all SO basins due to the presence or absence of regional bathymetric obstacles. The Antarctic Polar Front (APF), defined by the 3–5 °C surface temperature range and the 2 °C subsurface temperature minimum at 200 m, is particularly important for nutrient redistribution and biodiversity, influencing the soft tissue carbon pump in the modern SO. However, previous assessments of its migrations in the past, mostly based on a single metric or indirect observations, were not always robust. Here, we combine a new proxy for subsurface temperature (sub-ST) reconstructions based on radiolarian assemblages (sub-STrad), with relative abundance variations of key radiolarian species, and sea-surface temperatures (SST) reconstructions, based on diatom assemblages (SSTdiat), to refine estimations of the past mean APF locations in the Kerguelen Plateau (KP) region. Data from three sediment cores on a south (55°S) to north (47°S) transect are used to trace the mean APF locations for three climate states, glacials, peak-interglacials and mild-interglacials. Our results suggest that the APF, presently located south of Kerguelen Islands, shifted by 6–7 degrees of latitude and was located north of the KP during all glacial periods of the last 360 kyrs. This suggests that the ACC major flow interacted less with the bottom topography relative to its modern counterpart, probably resulting in less mixing of the water column over and in the lee of the KP. We propose that this process participated in the isolation of Antarctic surface waters (AASW) and in the reduction of macro-nutrient supply, thus resulting in lower regional productivity. During the warmer-than-present early interglacial periods, the APF probably migrated south by ~5 degrees of latitude relative to its modern position, to pass through the Fawn Trough. Contrary to glacial periods, the APF was forced in an “S” shape while the ACC main flow was constrained against the northern tip of the KP. In this configuration, a stronger interaction between the ACC, its associated fronts, and topography is expected, resulting in more mixing of the water column over and east of the KP. Congruently, siliceous productivity was probably restrained to latitudes south of the Fawn Trough.

Published
2021
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5. On new developments in accelerator mass spectrometry and how they promote our understanding of global carbon cycle dynamics during the last deglaciation

Author

Julia Gottschalk, Robert F. Anderson, David A. Hodell, Alfredo Martinez-Garcia, Alain Mazaud, Elisabeth Michel, Luke C. Skinner, Anja Studer, Sönke Szidat, Lena M. Thöle, and Samuel L. Jaccard

Abstract

Ocean-atmosphere 14C disequilibria of the surface and deep ocean reflect past changes in the efficiency of ocean-atmosphere CO2 exchange and ocean mixing, while it may also be related to variations in global-ocean respired carbon content. A full assessment of the oceanic mechanisms controlling deglacial changes in atmospheric CO2 is complicated by a lack of high-resolution 14C ventilation age estimates from the Southern Ocean and other key regions due to low foraminiferal abundances in marine sediments in those areas. Here we present high-resolution deglacial 14C ventilation age records from key sites in the Atlantic and Indian Sector of the Southern Ocean obtained by radiocarbon analyses of small benthic and planktic foraminiferal samples (3) with the UniBe Mini-Carbon Dating System (MICADAS). Our analyses specifically circumvent foraminiferal sample size requirements related to “conventional” accelerator mass spectrometer analyses involving sample graphitization (>1 mg CaCO3 in most laboratories). Complementing multi-proxy analyses of sea surface temperature (SST) changes at these sites allow the construction of a radiocarbon-independent age model through a stratigraphic alignment of SST changes to Antarctic (ice core) temperature variations. We demonstrate the value of refining the age models of our study cores on the basis of high-resolution sedimentary U- and Th flux estimates, which allows an improved quantification of surface ocean reservoir age variations in the past. The resulting deep-ocean ventilation age changes are compared against qualitative and quantitative indicators of bottom water [O2] variations, in order to assess the role of Southern Ocean overturning dynamics in respired carbon changes at our study sites. We discuss the implications of our new radiocarbon- and bottom water [O2] data for the ocean’s role in atmospheric CO2 changes throughout the last deglaciation, and evaluate down-stream effects of southern high-latitude surface ocean reservoir age anomalies.

Published
2020
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6. Glacial-interglacial dust and export production records from the Southern Indian Ocean

Author

H. Eri Amsler, Alexandra Auderset, Simone Moretti, Samuel L Jaccard, James Gilgannon, Xavier Crosta, Lena M Thöle, Elisabeth Michel, Alfredo Martínez-García, Alain Mazaud, Joerg Lippold, Hendrik Vogel, Oeschger Centre for Climate Change Research (OCCR), University of Bern, Helmholtz Zentrum für Umweltforschung = Helmholtz Centre for Environmental Research (UFZ), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Paléocéanographie (PALEOCEAN), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Marine isotope stage, Polar front, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Iron fertilization, 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, Oceanography, Ice core, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Interglacial, Earth and Planetary Sciences (miscellaneous), Ice age, Upwelling, 14. Life underwater, Glacial period, Geology, ComputingMilieux_MISCELLANEOUS, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences
Abstract

We present 230Th-normalized dust and export production fluxes for two contrasted marine sediment cores spanning the Antarctic Polar Front, close to the Kerguelen Plateau in the Southern Indian Ocean, covering the last glacial cycle. We report glacial lithogenic fluxes comparable to the South Atlantic and higher than in the South Pacific sectors of the Southern Ocean. Structural and temporal discrepancies with dust reconstructions from Antarctic ice cores and the Atlantic and Pacific sectors of the Subantarctic Zone (SAZ) point towards Southern Africa and/or the Kerguelen Plateau as an additional source of lithogenic material to the Southern Indian Ocean during the last ice age. In the SAZ, export production proxies respond to iron (Fe) fertilization with total organic carbon (TOC) fluxes as high as those previously reported from the Atlantic sector of the Southern Ocean. However, the correlation between export production and dust proxies is weaker than in the other sectors, and shows a muted response of export production during peak glacials. We hypothesize that this muted response may be related to macronutrient (co-)limitation imposed on phytoplankton growth possibly induced by a northward displacement of wind-driven upwelling and/or the polar frontal system during peak glacials. The Antarctic Zone (AZ) record depicts the typical pattern of enhanced export production during interglacials and comparatively low productivity during glacials suggesting a decrease in the supply of macronutrients to the AZ surface during ice ages compared to warm periods, as previously proposed. However, a muted response of opal fluxes during marine isotope stage (MIS) 5e argues for a southward migration of the frontal system during warmer MIS 5e, possibly causing silicic acid (co-)limitation at this site. These results illustrate the important role of Fe fertilization and changes in wind-driven upwelling intensities in modulating the strength and efficiency of the biological carbon pump in the Southern Ocean, but also highlight the potential role of frontal movements in explaining export production variability at sites located close to the Antarctic Circumpolar Current (ACC) fronts. Overall, our new datasets provide new insights on the regional differences in dust and export production patterns that need to be considered in order to evaluate the efficiency of carbon sequestration in the different sectors of the Southern Ocean during ice ages.

Published
2019
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7. Impact of the Agulhas Return Current on the oceanography of the Kerguelen Plateau region, Southern Ocean, over the last 40 kyrs

Author

Minoru Ikehara, Alain Mazaud, M. Civel-Mazens, Olivier Ther, Xavier Crosta, Giuseppe Cortese, Takuya Itaki, Elisabeth Michel, Kochi University, Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Climat et Magnétisme (CLIMAG), and EPOC - CNRS, UMR 5805

Subjects
010506 paleontology, Archeology, 010504 meteorology & atmospheric sciences, 01 natural sciences, Latitude, Water column, 14. Life underwater, Glacial period, ComputingMilieux_MISCELLANEOUS, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, Ecology, Evolution, Behavior and Systematics, Holocene, 0105 earth and related environmental sciences, Temperature record, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Polar front, Global and Planetary Change, biology, Geology, biology.organism_classification, Diatom, Oceanography, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, 13. Climate action, Return current
Abstract

The oceanography of the western Indian sector of the Southern Ocean is extremely complex due to the presence of several subantartic islands and plateaus that alter the zonal flow of the Antarctic Circumpolar Current. The circulation is even more complex around the Kerguelen Islands (KI) as the hydrological fronts merge with the Agulhas Return Current, the latter transporting warm surface waters from the low latitudes to the Subantarctic Zone (SAZ) east of KI. Here we present new sea-surface and sub-surface temperatures, based on diatom and radiolarian census counts respectively, in two cores covering the last 40,000 years (40 kyrs) to infer past oceanographic changes in the KI region. In core MD11-3353, located in the Polar Front Zone (PFZ) west of KI, both sea-surface and sub-surface temperatures follow the expected glacial-interglacial pattern, with a constant difference of ∼3 °C, suggesting that the structure of the top 500 m of the water column did not change drastically over this period. In core MD12-3396CQ, located in the SAZ east of KI, the sub-surface temperature record again follows the expected glacial-interglacial pattern while the diatom-based reconstruction shows a strong warming during the 40-24 kyrs period, with a mean difference between the two of ∼9 °C. The temperature difference subsequently reverts to ∼3 °C during the glacial termination and Holocene. We suggest that the large difference between surface and sub-surface temperatures during the 40-24 kyrs period resulted from the injection of warm surface waters from the Indian low latitudes. This signal was transported to the core site by a strengthened Agulhas Return Current during the glacial, when the Agulhas leakage to the Atlantic was reduced. Our study thus proposes that the surface conditions in the SAZ of the KI region are shaped by the interplay between the migration of the Southern Ocean hydrological fronts and the Agulhas (Return) Current, both being climatically modulated.

Published
2021
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8. Reconstruction of the last glacial-interglacial cycle in the Kerguelen Plateau's PFZ and SAZ, Southern Ocean

Author

Matthieu, Civel, Xavier, Crosta, Giuseppe, Cortese, Elisabeth, Michel, Alain, Mazaud, Lena, Thöle, Samuel, Jaccard, Minoru, Ikehara, and Takuya, Itaki

Abstract

The Ninth Symposium on Polar Science/Special session: [S] Antarctic ice-ocean interaction ～observation, reconstruction, and modeling～, Tue. 4 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research

Published
2018

9. Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO_2 rise

Author

Elisabeth Michel, Jörg Lippold, Alfredo Martínez-García, Laura F. Robinson, Anja S Studer, Jess F. Adkins, Lena M Thöle, Samuel L Jaccard, Alain Mazaud, Xingchen T. Wang, Gerald H. Haug, Daniel M. Sigman, Max Planck Institute for Chemistry (MPIC), Max-Planck-Gesellschaft, Princeton University, University of Bern, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Oeschger Centre for Climate Change Research (OCCR), Climat et Magnétisme (CLIMAG), Division of Geological and Planetary Sciences [Pasadena], California Institute of Technology (CALTECH), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, North Atlantic Deep Water, Biological pump, 010502 geochemistry & geophysics, 01 natural sciences, Deep sea, Deposition (geology), Waves and shallow water, chemistry.chemical_compound, Oceanography, chemistry, 13. Climate action, Interglacial, General Earth and Planetary Sciences, Environmental science, Carbonate, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Holocene, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

A rise in the atmospheric CO2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO2, and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO2 in the ocean interior, possibly explaining the Holocene atmospheric CO2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene.

Published
2018
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10. Radiocarbon Measurements of Small-Size Foraminiferal Samples with the Mini Carbon Dating System (MICADAS) at the University of Bern: Implications for Paleoclimate Reconstructions

Author

Gary Salazar, Jörg Lippold, Julia Gottschalk, Michael Battaglia, Sönke Szidat, Elisabeth Michel, Alain Mazaud, Samuel L Jaccard, Paul Scherrer Institute ( PSI ), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] ( LSCE ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Université Paris-Saclay-Centre National de la Recherche Scientifique ( CNRS ), Oeschger Centre for Climate Change Research ( OCCR ), University of Bern, Oeschger Centre for Climate Change Research (OCCR), Paul Scherrer Institute (PSI), Paléocéanographie (PALEOCEAN), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[ SDU.OCEAN ] Sciences of the Universe [physics]/Ocean, Atmosphere, 010506 paleontology, Archeology, 010504 meteorology & atmospheric sciences, Mineralogy, 01 natural sciences, law.invention, Foraminifera, chemistry.chemical_compound, 14C backgrounds, Absolute dating, law, Paleoclimatology, [ SDU.ENVI ] Sciences of the Universe [physics]/Continental interfaces, environment, Radiocarbon dating, Indian Ocean, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Standard material, MICADAS, biology, foraminifera, biology.organism_classification, chemistry, 13. Climate action, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Reference values, General Earth and Planetary Sciences, Carbonate, AMS dating, Geology, Accelerator mass spectrometry
Abstract

Radiocarbon (14C) measurements of foraminifera often provide the only absolute age constraints in marine sediments. However, they are often challenging as their reliability and accuracy can be compromised by reduced availability of adequate sample material. New analytical advances using the MIni CArbon DAting System (MICADAS) allow 14C dating of very small samples, circumventing size limitations inherent to conventional 14C measurements with accelerator mass spectrometry (AMS). Here we use foraminiferal samples and carbonate standard material to assess the reproducibility and precision of MICADAS 14C analyses, quantify contamination biases, and determine foraminiferal 14C blank levels. The reproducibility of conventional 14C ages for our planktic (benthic) foraminiferal samples from gas measurements is 200 (130) yr, and has good precision as illustrated by the agreement between both standards and their reference values as well as between small gas- and larger graphitized foraminiferal samples (within 100±60 yr). We observe a constant contamination bias and slightly higher 14C blanks for foraminifera than for carbonate reference materials, limiting gas (graphite) 14C age determinations for foraminifera from our study sites to ~38 (~42) kyr. Our findings underline the significance of MICADAS gas analyses for 14C on smaller-than-conventional sized foraminiferal samples for paleoclimate reconstructions and dating.

Published
2018
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11. The paleomagnetic record at IODP Site U1307 back to 2.2 Ma (Eirik Drift, off south Greenland)

Author

Joseph S. Stoner, James E.T. Channell, Alain Mazaud, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Climat et Magnétisme (CLIMAG), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), University of Florida [Gainesville] (UF), College of Earth, Ocean and Atmospheric Sciences [Corvallis] (CEOAS), Oregon State University (OSU), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, 010504 meteorology & atmospheric sciences, Sediment, Drilling, Context (language use), 010502 geochemistry & geophysics, 01 natural sciences, Seafloor spreading, Current (stream), Paleontology, Geophysics, Oceanography, Space and Planetary Science, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Sedimentary rock, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Quaternary, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

Integrated Ocean Drilling Program (IODP) Expedition 303 to the North Atlantic in 2004 recovered a 175-m Quaternary sedimentary section at IODP Site U1307, located on the northern part of the Eirik Drift, south of Greenland. The seafloor at Site U1307, at 2575 m water depth, is situated within the water-depth range of the present-day main axis of the Western Boundary Under Current (WBUC) but lies on the NW side of the drift crest and is partly shielded from it. The uppermost 120 meters of sediment sequence were sampled with u-channels along a composite section which combines the two holes drilled at this site. An age model was obtained by identification of polarity reversals back to the Reunion Subchron ( ∼ 2.1 Ma ) and then refined in the 0–1.5 Ma interval by correlation of the relative paleointensity (RPI) record to the PISO paleointensity stack. The Site U1307 relative paleointensity (RPI) record is compared with the PISO and EPAPIS (Pacific) stacks, neighboring IODP sites from Eirik Drift (Sites U1305 and U1306), and with the Ocean Drilling Program (ODP) Site 984 record that extends beyond PISO. Magnetite grain-size and concentration proxies are compared to Sites U1305 and U1306 records, in the context of the past evolution of the WBUC.

Published
2015
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12. Upper and lower Jaramillo polarity transitions recorded in IODP Expedition 303 North Atlantic sediments: Implications for transitional field geometry

Author

Chuang Xuan, Alain Mazaud, Joseph S. Stoner, James E.T. Channell, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), University of Florida [Gainesville] (UF), College of Oceanic and Atmospheric Sciences [Corvallis], Oregon State University (OSU), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Jaramillo reversal, 010504 meteorology & atmospheric sciences, Physics and Astronomy (miscellaneous), Field (physics), Polarity (physics), Astronomy and Astrophysics, Geometry, Geomagnetic pole, Geophysics, 010502 geochemistry & geophysics, 01 natural sciences, Earth's magnetic field, 13. Climate action, Space and Planetary Science, South american, Physical Sciences, Paleointensity, 14. Life underwater, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

Sediments collected during the Integrated Ocean Drilling Program (IODP) Expedition 303 in the North Atlantic provide records of polarity transitions and geomagnetic excursions at a high resolution. Here we investigate polarity transitions at the upper and lower boundaries of the Jaramillo subchronozone at Sites U1305, U1304, and U1306. The sediments carry strong natural remanent magnetizations (NRM) with median destructive fields consistent with magnetite as the dominant magnetic carrier. Both polarity transitions are characterized by low values of relative paleointensity. The U1305 record of the lower Jaramillo reversal exhibits a marked cluster of virtual geomagnetic poles (VGPs) over southern South America, and a secondary accumulation in the region of NE Asia/North Pacific. The main South American VGP cluster is also visible at Site U1304, which documents a less complex pattern, possibly because of a higher degree of smoothing. Records of the upper Jaramillo polarity transition document a VGP loop over the Americas, followed by north to south motion including a secondary VGP accumulation near India. The similarity between several records of the upper Jaramillo transition obtained at various sites in the North Atlantic is a strong indication that geomagnetic field changes have been faithfully captured. Results suggest that a transverse, possibly dipolar, field component has fluctuated during these polarity reversals, and that these fluctuations combined with a reduced axial dipole component yielded the observed field at the Earth’s surface during the polarity transitions. The lower Jaramillo transition also exhibits VGP clusters in the vicinity of South America and eastern Asia but these clusters are shifted relative to the upper Jaramillo VGP clusters, implying a memory exerted by the upper mantle on polarity transition geometry.

Published
2009
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13. Age through tandem correlation of Quaternary relative paleointensity (RPI) and oxygen isotope data at IODP Site U1306 (Eirik Drift, SW Greenland)

Author

James D. Wright, James E.T. Channell, Joseph S. Stoner, Alain Mazaud, University of Florida [Gainesville] (UF), Rutgers, The State University of New Jersey [New Brunswick] (RU), Rutgers University System (Rutgers), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), College of Oceanic and Atmospheric Sciences [Corvallis], Oregon State University (OSU), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Archeology, Global and Planetary Change, biology, Sediment, Geology, biology.organism_classification, Isotopes of oxygen, law.invention, Foraminifera, Oceanography, law, Interglacial, Deglaciation, 14. Life underwater, Glacial period, Radiocarbon dating, Quaternary, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Ecology, Evolution, Behavior and Systematics, ComputingMilieux_MISCELLANEOUS
Abstract

Planktic oxygen isotope (δ 18 O) and relative paleointensity (RPI) data are used in tandem to generate an age model for the last 1 Myr from Integrated Ocean Drilling Program (IODP) Site U1306 drilled on the crest of the Eirik Drift (SW Greenland) in 2272 m water depth. For the 1–1.5 Ma interval, the age model is based on RPI alone due to insufficient foraminifera for isotope analyses. Utilizing RPI and δ 18 O in tandem allows recognition of low-δ 18 O “events” prior to glacial Terminations I, III, IV, V, VII, VIII, IX and X, that are independently supported by radiocarbon dates through the last deglaciation, and are attributed to local or regional surface-water effects. At Site U1306, Quaternary sedimentation rates (mean ∼15 cm/ka) are elevated during peak glacials and glacial onsets, and are reduced during interglacials, in contrast to the pattern at Site U1305 in 3460 m water depth at the distal toe of the drift, 191 km SW of Site U1306. The contrasting sedimentation-rate pattern appears to hold for the entire ∼1.5 Myr record. The slackening and/or shoaling (due to lowered salinity) of the Deep Western Boundary Current (DWBC) during glacial intervals coincided with greater sediment supply to Site U1306 whereas the deepening, and possibly increased vigor, of the DWBC during interglacial intervals boosted sediment supply to Site U1305.

Published
2014
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14. North Atlantic palaeointensity stack since 75ka (NAPIS–75) and the duration of the Laschamp event

Author

Alain Mazaud, Catherine Kissel, Juerg Beer, Carlo La j, James E.T. Channell, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), University of Florida [Gainesville] (UF), Swiss Federal Insitute of Aquatic Science and Technology [Dübendorf] (EAWAG), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, Paleomagnetism, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, General Mathematics, Stack (geology), General Engineering, General Physics and Astronomy, 010502 geochemistry & geophysics, 01 natural sciences, Paleontology, Oceanography, Duration (music), Geomagnetic excursion, Laschamp event, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

Six relative palaeointensity records from the north Atlantic Ocean were stacked together to produce a new record for the last 75 kyr (NAPIS75). Five of these records have been previously correlated...

Published
2000
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15. The top Olduvai polarity transition at ODP Site 983 (Iceland Basin)

Author

Alain Mazaud, James E.T. Channell, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), University of Florida [Gainesville] (UF), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, 010504 meteorology & atmospheric sciences, Polarity (physics), Geomagnetic pole, Geophysics, Structural basin, 010502 geochemistry & geophysics, 01 natural sciences, Latitude, Space and Planetary Science, Geochemistry and Petrology, Remanence, Paleointensity, Earth and Planetary Sciences (miscellaneous), [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

The composite section obtained from ODP Site 983 has been sampled in the vicinity of the top Olduvai polarity transition using the u-channel technique. The polarity transition occurs in a normalized remanence (paleointensity) low with post-reversal recovery in paleointensity but no systematic decay in paleointensity in the Matuyama Chron above the reversal. The directional change associated with the reversal extends over about one meter depth, with a virtual geomagnetic pole (VGP) path which indicates a number of loops over Canada and the North Atlantic, prior to a path over the Americas to a VGP cluster in the South Atlantic, off Argentina. The path then leads to a VGP cluster over India, then a loop over the Caribbean and transits through the Atlantic to high southerly latitudes. VGP clusters in the transition path are observed at positions which are broadly similar to those seen in the top Jaramillo transition at the same site, may imply a memory effect in the geodynamo spanning successive reversals of the same sense.

Published
1999
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16. Magnetic anisotropy and environmental changes in two sedimentary cores from the Norwegian Sea and the North Atlantic

Author

Trond Dokken, Catherine Kissel, Alain Mazaud, Carlo Laj, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Climat et Magnétisme (CLIMAG), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), University of Bergen (UiB), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
010504 meteorology & atmospheric sciences, Natural remanent magnetization, 010502 geochemistry & geophysics, 01 natural sciences, Sedimentary depositional environment, Paleontology, Ice core, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, Plateau, geography.geographical_feature_category, Geophysics, Magnetic susceptibility, Magnetic anisotropy, 13. Climate action, Space and Planetary Science, Remanence, Interglacial, Geology
Abstract

We have studied the magnetic properties and the magnetic anisotropy (AMS and AARM) of cores MD95-2010 from the Voering Plateau and SU90-33 from the south Icelandic basin. In the first core, the study has been focussed on climatic stage 3 during which the record of magnetic susceptibility is correlated with the δ18O signal from the Greenland ice cores. Minima (maxima) in susceptibility, anhysteretic remanent magnetization and isothermal remanent magnetization coincide with cold (warm) periods and reflect a modulation in the amount of deposited magnetite. In the second core six climatic stages have been studied. The AMS and the AARM changes are tightly correlated, showing that both are related to changes in the organization of magnetite grains in the sediment. Both magnetic fabrics are oblate and the variations of the degree of anisotropy are climatically controlled with higher values during short warm events or interglacial periods compared to cold periods. Different possible mechanisms leading to the observed fabrics are discussed. It appears that, although a differential compaction might have been active, the fabrics mainly result from depositional effects, in connection with climatic changes. Although the exact mechanisms of the link between magnetic fabrics and bottom current dynamics are, as yet, open to discussion, the study of magnetic anisotropy, which reflects the sedimentary structure, may ultimately lead to a better understanding of the coupling between atmospheric temperature changes and paleocirculation pattern in the North Atlantic and Nordic Seas.

Published
1998
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17. A database for the Matuyama-Brunhes magnetic reversal

Author

Jeffrey J. Love, Alain Mazaud, Department of Earth Sciences [Leeds], University of Leeds, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Data collection, 010504 meteorology & atmospheric sciences, Physics and Astronomy (miscellaneous), Database, Lava, Astronomy and Astrophysics, Geomagnetic pole, 010502 geochemistry & geophysics, computer.software_genre, 01 natural sciences, Geomagnetic reversal, Data set, Geophysics, Space and Planetary Science, Temporal resolution, Sedimentary rock, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, computer, ComputingMilieux_MISCELLANEOUS, Geology, 0105 earth and related environmental sciences
Abstract

We present a paleomagnetic database, designated MBD97, comprising sedimentary and lava data for the Matuyama-Brunhes reversal transition field. Using criteria regarding suitability of the rock samples, measurement methods and temporal resolution of the data, we consider 62 different studies of the Matuyama-Brunhes reversal; of these, only 11 satisfy our selection criteria: four lava sites, one loess site, three shallow-marine sedimentary sites, and three deep-ocean sedimentary sites. We discuss our reasons for accepting or disguarding each candidate data set. We investigate the distribution of transitional virtual geomagnetic poles (VGPs); they fall along American and Asian-Australian longitudes. The spatial and temporal complexity of the data indicate that the transitional field was almost certainly nonaxisymmetric and nondipolar. The directional transition of the Matuyama-Brunhes reversal took ∼ 2300–5000 years, during which time the surface intensity fell to ∼ 10–20% of its pre- and post-transitional value. We do not find any systematic bias due to site distribution or inclination shallowing, although the errors in the data do vary over the duration of the reversal. MBD97 is a small database, but it has a fairly good geographic distribution and is suitable for studies of the Matuyama-Brunhes transition, nonetheless, it is clear that further analysis of transitions will benefit from a continued program of data collection and analysis. The data in MBD97 are listed.

Published
1997
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18. Relative changes of the geomagnetic field intensity during the last 280 kyear from piston cores in the Açores area

Author

Catherine Kissel, Martine Paterne, Carlo Laj, Alain Mazaud, Laurent Labeyrie, Benoı̂t Lehman, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, Physics and Astronomy (miscellaneous), Mineralogy, Astronomy and Astrophysics, Geophysics, Isotopes of oxygen, Magnetization, chemistry.chemical_compound, Earth's magnetic field, Volcano, chemistry, Space and Planetary Science, Remanence, Sedimentary rock, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, Geology, Intensity (heat transfer), Magnetite
Abstract

Relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the Acores area. One core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation. Rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain-size distribution in the pseudo-single domain range for the three cores. Changes in the amount of magnetite do not exceed a factor of 10. Therefore, these cores appear to be suitable for relative palaeointensity determinations. Two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation (NRM), but the power at these frequencies is not significant at the 95% level for the normalised remanence records. For each core, normalisation of the NRM using different normalising parameters yields virtually identical results. Using saturation isothermal remanent magnetisation (SIRM) as the normalising parameter, the results of the three cores were then combined into a stacked curve. Squared coherence analysis between this stacked curve and bulk mineral-magnetic parameters reveals that the 18 kyear component is still present in the record, but that the power spectrum is barely above noise level at this frequency. Some of the features of this North Atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records. For instance, distinct periods of low intensity are observed around 40, 120, and 190 kyears, and periods of high intensity at 50 and 80 kyears. Because of the uniformity of the mineral-magnetic characteristics of the three cores, we suggest that this record may be a suitable palaeointensity reference curve for the Central North Atlantic Ocean region.

Published
1996
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19. Relative paleointensity and environmental magnetism since 1.2Ma at IODP site U1305 (Eirik Drift, NW Atlantic)

Author

Alain Mazaud, James E.T. Channell, Joseph S. Stoner, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), University of Florida [Gainesville] (UF), College of Oceanic and Atmospheric Sciences [Corvallis], Oregon State University (OSU), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Milankovitch cycles, 010504 meteorology & atmospheric sciences, Environmental magnetism, Terrigenous sediment, Detritus (geology), 010502 geochemistry & geophysics, 01 natural sciences, Isotopes of oxygen, Geophysics, Oceanography, Space and Planetary Science, Geochemistry and Petrology, Interglacial, Earth and Planetary Sciences (miscellaneous), 14. Life underwater, Glacial period, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Integrated Ocean Drilling Program (IODP) Expedition 303 to the North Atlantic in 2004 recovered rapidly deposited deep-sea sediments at IODP Site U1305 on Eirik Drift, located south of Greenland at 3460 m water depth, along the path of the Western Boundary Under Current (WBUC). About 200 m of sediment was sampled with u-channels from the composite section, providing a continuous record of paleomagnetic field directions and relative paleointensity (RPI) variations covering the past 1.2 Myr. The age model, based on an oxygen isotope record, is consistent with the fit of the RPI record to a calibrated template, and indicates higher sedimentation rates during interglacials relative to glacial epochs. Magnetite grain-size and concentration proxies indicate higher concentrations of magnetite with larger grain sizes during interglacials. Enhanced interglacial deposition can be attributed to a combination of elevated entrainment of terrigenous detritus into the WBUC due to glacial retreat on continents flanking the upstream path of the WBUC (east Greenland and Iceland), and of increased bottom current (WBUC) vigor leading to elevated transport and deposition at the site during interglacials. This pattern is opposite to observations of flow of the Antarctic circum polar current (ACC) in the south Indian Ocean, which suggests an inter-hemispheric antiphase in marine circulation at the Milankovitch scale, with strong circulation in the deep North Atlantic when the ACC is weak, and vice versa.

Published
2012
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20. The Matuyama-Brunhes and Upper Jaramillo transitions recorded in a loess section at Weinan, north-central China

Author

Alain Mazaud, Carlo Laj, Rixiang Zhu, Chinese Academy of Sciences [Beijing] (CAS), Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Natural remanent magnetization, Lithology, Polar wander, Geomagnetic pole, Paleontology, Geophysics, Space and Planetary Science, Geochemistry and Petrology, Loess, Earth and Planetary Sciences (miscellaneous), [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Quaternary, Longitude, ComputingMilieux_MISCELLANEOUS, Seismology, Geology
Abstract

The paleomagnetic records of the Matuyama-Brunhes (MB) and Upper Jaramillo (UJ) polarity reversals have been obtained from a loess section at Weinan, Shaanxi province, in China. An investigation of the rock magnetic properties using stepwise IRM acquisition, hysteresis loops, thermomagnetic analysis and X-ray diffraction on magnetic extracts, identifies pseudo-single domain magnetite as the carrier of the main fraction of the remanence, associated with maghemite and hematite. The total duration of the directional change (based upon independent loess accumulation rates), is about 5000 yr for the MB reversal and about 3200 yr for the UJ reversal. These values are consistent with previous estimates obtained from marine or lacustrine sediments. Apart from a few intermediate points observed on North America (MB) and in the Pacific (UJ), the transitional Virtual Geomagnetic Pole (VGP) paths are situated in two longitudinal bands over eastern Asia and Australia (MB) and the Americas (UJ). The bulk of the UJ record and the part of the MB record over the Americas are not consistent with the hypothesis of a record arising from smoothing of pre- and post-transitional directions [1]. A reappraisal of the statistical approach of McFadden et al. [2] shows that the longitudinal distribution of the records of reversals is consistent with the hypothesis of genuine, geographically preferred sectors for the paths, independent of site longitude, with a probability higher than 0.45 when the two Weinan records are considered. Thus, these results, obtained from wind-blown loess, sustain the hypothesis of two preferential longitudinal bands for reversing transitional VGPs suggested from the study of marine and lacustrine sediments.

Published
1994
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21. The Blake Geomagnetic Polarity Episode recorded in Chinese loess

Author

Liping Zhou, Carlo Laj, Zhongli Ding, Rixiang Zhu, and Alain Mazaud

Subjects
Paleontology, Paleomagnetism, Geophysics, Earth's magnetic field, Stratigraphy, Pleistocene, Polarity (physics), Loess, General Earth and Planetary Sciences, Magnetic anomaly, Magnetostratigraphy, Geology
Abstract

A geomagnetic anomaly consisting of three clearly defined periods of reverse polarity separated by two short intervals of normal polarity has been documented in a loess section near Xining, western China. On the basis of previous studies of Chinese loess stratigraphy, we correlate this geomagnetic polarity episode with the Blake event. While more research is needed to improve our understanding of the exact process of remanence acquisition of loess deposits, this study shows that loess may provide records of fast geomagnetic events and lends further support to the global nature of the Blake geomagnetic event.

Published
1994
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22. Benthic foraminiferal abundance and stable isotope changes in the Indian Ocean sector of the Southern Ocean during the last 20 kyr: Paleoceanographic implications

Author

Alain Mazaud, Claire Waelbroeck, Elisabeth Michel, Christopher W. Smart, School of Geography, Earth and Environmental Sciences [Plymouth] (SoGEES), Plymouth University, Paléocéanographie (PALEOCEAN), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010506 paleontology, 010504 meteorology & atmospheric sciences, δ18O, Phytodetritus, Paleontology, Oceanography, 01 natural sciences, Deep sea, Benthic zone, Paleoceanography, Deglaciation, 14. Life underwater, Glacial period, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Ecology, Evolution, Behavior and Systematics, Holocene, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Earth-Surface Processes
Abstract

Benthic foraminiferal faunas and benthic stable isotopes during the last 20 kyr were investigated in core MD02-2488 (46°28.8′S, 88°01.3′E, 3420 m water depth) from the southeast Indian Ocean sector of the Southern Ocean in order to document paleoceanographic changes from the last glacial, through deglaciation and into the Holocene. Variations occurred in the accumulation rates, species composition, diversity, and stable isotopes during the last 20 kyr. The benthic δ18O and δ13C records during the last ~ 28 kyr show that no significant deep water circulation changes took place before ~ 15.6 calendar kyr (ka). The δ13C increase at 15.6 ka is interpreted as reflecting the arrival of better ventilated deep waters at the site and is associated with the progressive increase in % of miliolids from ~ 15 ka to 0 ka, an interval (~ 16–15 ka) of low benthic foraminiferal accumulation rates (BFARs) and an increase in the relative abundance of Stainforthia complanata. Deep waters were ~ 2.2 ± 0.4 °C colder during the last glacial than at present. Carbonate dissolution proxies indicate that carbonate dissolution was higher during the last glacial than during the last deglacial and Holocene. BFARs and the percentage of species indicative of high-productivity suggest that the flux of organic matter resulting from surface water productivity was generally higher between ~ 20 and 13 ka than between ~ 12 and 0 ka, consistent with the observed higher proportion of biosiliceous sediment at ~ 20–14 ka and published records. The combined percentages of the two most abundant species, Alabaminella weddellensis and Epistominella exigua (‘phytodetritus species’), suggest that seasonality of productivity (intermittency of primary productivity) fluctuated over the last 20 kyr and was higher during the last glacial and deglaciation (20–10 ka) compared with the Holocene (10–0 ka). The relative abundances of A. weddellensis and E. exigua do not covary over the last 20 kyr, an observation also reported from other areas.

Published
2010
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23. Variations of the Antarctic Circumpolar Current intensity during the past 500 ka

Author

E. Michel, Fabien Dewilde, Alain Mazaud, and Jean-Louis Turon

Subjects
geography, Plateau, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Environmental magnetism, 010502 geochemistry & geophysics, 01 natural sciences, Grain size, Geophysics, Oceanography, Ice core, Geochemistry and Petrology, Abundance (ecology), Middle latitudes, Interglacial, 14. Life underwater, Glacial period, Geology, 0105 earth and related environmental sciences
Abstract

[1] We examine the past variations of the Antarctic Circumpolar Current (ACC) by using variations in size and abundance of the magnetic grains deposited by this current at a site east the Kerguelen-Crozet plateau. Core MD00-2375G was taken at a midlatitude site during the ANTAUS cruise conducted in 2000 by the French R/V Marion Dufresne. Marine isotope stages (MIS) down to MIS 13 are identified, and an age model is derived from a correlation to the ice core isotopic record obtained from EPICA in Antarctica. Continuous records of abundance and size of the magnetic grains were obtained using environmental magnetism methods. Results show a strong modulation of the ACC flow intensity in response to glacial and interglacial cycles. The low abundance and the small size of magnetic grains indicate that the ACC was weak during warm stages and strong during glacial epochs. A large modulation is also observed at the sub-stage scale during the interglacials. A minimum in concentration and grain size occurs at the onset of MIS 11. At the MIS 6–5, 10–9, and possibly 12–11 transitions, observed variations suggest a mechanism involving both rapid and progressive variations of the ACC flow at deglaciations.

Published
2010
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24. Lake Ohrid, Albania, provides an exceptional multi-proxy record of environmental changes during the last glacial–interglacial cycle

Author

Jean-Jacques Tiercelin, Amandine Bordon, U. von Grafenstein, Soumaya Belmecheri, Eric Fouache, Cedric Robert, Christophe Grenier, P. Huntsman-Mapila, D. Hureau-Mazaudier, Z. Zeqollari, Giovanni Zanchetta, Alain Mazaud, Roberto Sulpizio, Helmut Erlenkeuser, Benoit Caron, Jean-Pierre Cazet, D. Manelli, Anne-Marie Lézine, Nils Andersen, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Géochrononologie Traceurs Archéométrie (GEOTRAC), Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Christian-Albrechts-University, Interactions et dynamique des environnements de surface (IDES), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Pise, Laboratoire de géographie physique : Environnements Quaternaires et Actuels (LGP), Université Paris 1 Panthéon-Sorbonne (UP1)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Modélisation Hydrologique (HYDRO), Harry Oppenheimer Okavango Research Centre, University of Botswana, Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Geological Survey, Pogradec, Climat et Magnétisme (CLIMAG), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), CIRISIVU Dpto Geomineralogico, Università degli studi di Bari Aldo Moro (UNIBA), Géosciences Rennes (GR), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Dipartimento di Scienze della Terra [Pisa], University of Pisa - Università di Pisa, MAFAK - Mission archéologique franco-albanaise du bassin de Korçë (Albanie), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Università degli studi di Bari Aldo Moro = University of Bari Aldo Moro (UNIBA), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] ( LSCE ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Université Paris-Saclay-Centre National de la Recherche Scientifique ( CNRS ), Leibniz-Lab, Radiometric Dating & Stable Isotope Research Institute, Laboratoire Chrono-environnement ( LCE ), Université Bourgogne Franche-Comté ( UBFC ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Franche-Comté ( UFC ), Interactions et dynamique des environnements de surface ( IDES ), Université Paris-Sud - Paris 11 ( UP11 ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Centre National de la Recherche Scientifique ( CNRS ), Pétrologie, géochimie, minéralogie magmatiques ( PGM2 ), Institut des Sciences de la Terre de Paris ( iSTeP ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Centre National de la Recherche Scientifique ( CNRS ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Centre National de la Recherche Scientifique ( CNRS ), EA 435 Géonat, Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ), Laboratoire de géographie physique ( LGP ), Université Panthéon-Sorbonne ( UP1 ) -Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ) -Centre National de la Recherche Scientifique ( CNRS ), Domaines Océaniques ( LDO ), Centre National de la Recherche Scientifique ( CNRS ) -Institut d'écologie et environnement-Observatoire des Sciences de l'Univers-Université de Brest ( UBO ) -Institut national des sciences de l'Univers ( INSU - CNRS ), Université européenne de Bretagne ( UEB ), Geological Survey, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace ( LPC2E ), Centre National de la Recherche Scientifique ( CNRS ) -Université d'Orléans ( UO ) -Institut national des sciences de l'Univers ( INSU - CNRS ), Università degli studi di Bari, Dipartimento di Scienze della Terra, Università di Pisa, Département des sciences de la Terre, Université Paris-Sud - Paris 11 (UP11), Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12), Harry Oppenheimer Okavango Research Center, Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre Armoricain de Recherches en Environnement-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Chrono-environnement - UFC (UMR 6249) (LCE), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Pétrologie, géochimie, minéralogie magmatiques (PGM2), Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Panthéon-Sorbonne (UP1), Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Université européenne de Bretagne - European University of Brittany (UEB), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université de Rennes 2 (UR2), and Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Multi-proxy approach, 010504 meteorology & atmospheric sciences, Lake-effect snow, [SDE.MCG]Environmental Sciences/Global Changes, Climate change, Palaeoenvironments, 010502 geochemistry & geophysics, Oceanography, Permafrost, 01 natural sciences, Paleontology, Paleoclimatology, Younger Dryas, Glacial period, [ SDU.STU.MI ] Sciences of the Universe [physics]/Earth Sciences/Mineralogy, Ecology, Evolution, Behavior and Systematics, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Earth-Surface Processes, 15. Life on land, Ohrid, 13. Climate action, [SDU]Sciences of the Universe [physics], [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Interglacial, Albania, Last climatic cycle, Physical geography, Quaternary, Geology, [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
Abstract

International audience; Multi-proxy analyses on core JO2004-1 recovered from Lake Ohrid (40°55.000 N, 20°40.297E, 705 m a.s.l.) provide the first environmental and climate reconstruction in a mountainous area in Southern Europe over the last 140,000 years. The response of both lacustrine and terrestrial environments to climate change has been amplified by the peculiar geomorphological and hydrological setting, with a steep altitudinal gradient in the catchment and a karstic system feeding the lake. The karstic system was active during interglacials, leading to high carbonate production in the lake, and blocked during glacials as a result of extremely cold climate conditions with permafrost in the mountains. At the Riss–Eemian transition (Termination 2) the increase in lacustrine productivity predated forest expansion by about 10,000 years. In contrast, the Late Glacial–Holocene transition (Termination 1) was characterized by the dramatic impact of the Younger Dryas, which initially prevented interglacial carbonate production and delayed its maximum until the mid-Holocene. In contrast, forest expansion was progressive, starting as early as ca. 38,000 ago. The proximity of high mountains and the probable moderating lake effect on local climate conditions promoted forest expansion, and contributed to make the surroundings of Lake Ohrid favourable to forest refugia during the last glacial, usually steppic, period. Our study of sedimentology, mineralogy, geochemistry, magnetics, palynology and isotopes illustrates the non-linear response of terrestrial and lacustrine ecosystems to similar climate events, and demonstrates the potential of Lake Ohrid as an excellent paleoclimatic archive during the Quaternary.

Published
2010
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25. Geomagnetic field control of14C production over the last 80 Ky: Implications for the radiocarbon time-scale

Author

Carlo Laj, Emmanuel Tric, Edouard Bard, Maurice Arnold, Alain Mazaud, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Box model, Scale (ratio), Atmospheric sciences, Carbon cycle, law.invention, Geophysics, Earth's magnetic field, law, Climatology, Period (geology), General Earth and Planetary Sciences, Radiocarbon dating, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Magnetic dipole, Geology
Abstract

International audience; We have used a recent estimate of the geomagnetic dipole field strength over the last 80 ky to examine the extent to which changes in geomagnetic field intensity have affected the radiocarbon time scale. The magnetic record was converted into a $^{14}$C production signal which was then used to produce a synthetic atmospheric $\Delta$$^{14}$C record using a two box model for the carbon cycle. This calibration suggests that the geomagnetic field has been the main factor governing the production of cosmogenic $^{14}$C atoms over the period of time considered, and that $\Delta$$^{14}$C changes due to other causes, such as climatic changes, have been of lesser importance. The results indicate that the radiocarbon ages are 2 to 3 ky younger than true age in the interval 18-40 ky b.p., in good agreement with recent U-Th and $^{14}$C age comparisons. Moreover the results predict that a negligible difference between true and $^{14}$C ages should be observed around 45-50 ky.

Published
1991
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26. An ice core perspective on the age of the Matuyama-Brunhes boundary

Author

Grant M. Raisbeck, Alain Mazaud, Jean Jouzel, Yohan Guyodo, Gabrielle Dreyfus, Frédéric Parrenin, Sébastien Nomade, Institut Pierre-Simon-Laplace (IPSL), École normale supérieure - Paris (ENS Paris)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National d'Études Spatiales [Toulouse] (CNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Department of Geosciences [Princeton], Princeton University, CSNSM AS, Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Université Joseph Fourier - Grenoble 1 (UJF), Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Paléocéanographie (PALEOCEAN), Climat et Magnétisme (CLIMAG), École normale supérieure - Paris (ENS-PSL), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
010504 meteorology & atmospheric sciences, [PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Ice stream, [SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP], Magnitude (mathematics), Flux, Geophysics, 010502 geochemistry & geophysics, 01 natural sciences, Core (optical fiber), Paleontology, Dome (geology), Ice core, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, Absolute dating, Earth and Planetary Sciences (miscellaneous), Geology, 0105 earth and related environmental sciences, Chronology
Abstract

Two intervals of enhanced 10Be flux thought to be associated with periods of low dipole intensity and identified as the Matuyama–Brunhes transition and a precursor event have been observed in the bottom section of the EPICA Dome C ice core. The peaks span 764–776 ka and 788–798 ka on the new EDC3 chronology with a stated absolute age uncertainty of 6 ka (2σ). This chronology uses orbital tuning of atmospheric oxygen-18 (δ18Oatm) to correct for anomalies in ice flow in the bottom 500 m of the core. An additional 28 δ18Oatm data points have been measured to improve resolution and verify the accuracy of the tuning and the stated timescale uncertainty. Both the dating of the increased 10Be, and that relative to climatic records, are compared to paleointensity records found in orbitally tuned marine sediments. The mid-point of the 10Be peak associated with the M-B is approximately 10 ka younger than the age determined radioisotopically from lavas with transitional orientations, taking into account recent revisions to the 40Ar/39Ar dating standard and improved precision. Climatic constraints on the EDC3 agescale make an error of this magnitude in the ice chronology implausible. This age difference, however, is consistent with recent modeling suggesting that directional changes are spatially asynchronous, and may precede the dipole intensity minimum in some locations. Although formally less precise than the published age from astrochronologically dated marine sediments, ice core ages are potentially more accurate because they are not subject to lock-in depth uncertainties.

Published
2008
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27. Age calibrated relative paleointensity for the last 1.5 Myr at IODP Site U1308 (North Atlantic)

Author

Chuang Xuan, Alain Mazaud, Joseph S. Stoner, David A. Hodell, James E.T. Channell, University of Florida [Gainesville] (UF), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), College of Oceanic and Atmospheric Sciences [Corvallis], Oregon State University (OSU), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, 010504 meteorology & atmospheric sciences, Wavelet coherence, Excursion, 010502 geochemistry & geophysics, 01 natural sciences, Isotopes of oxygen, Paleontology, Geophysics, Oceanography, Earth's magnetic field, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, Paleointensity, Earth and Planetary Sciences (miscellaneous), 14. Life underwater, Linear correlation, Quaternary, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Integrated Ocean Drilling Program (IODP) Site U1308 (central North Atlantic) records paleomagnetic directional and relative paleointensity (RPI) variations for the last 1.5 Myr, in 110 m of the sediment sequence at a mean sedimentation rate of 7.3 cm/kyr. A detailed benthic oxygen isotope record was combined with RPI to produce an integrated, high-resolution magneto-isotopic stratigraphy for Site U1308. Apart from the well-known polarity reversals in this interval, the Punaruu excursion is recorded at 1092 ka and the Cobb Mountain Subchron in the 1182–1208 ka interval. The paleointensity proxies are determined as slopes of NRM versus ARM and NRM versus ARMAQ (ARM acquisition) with linear correlation coefficients to monitor the quality of the linear fit. The RPI record for Site U1308 is compared with the three other paleointensity records (one from the Western Equatorial Pacific and two from the North Atlantic) that cover the same time interval and have accompanying oxygen isotope records. The Match protocol of Lisiecki and Lisiecki (2002) is used to optimize the correlation of paleointensity records. Beginning with the original (published) age models for each record, the Match routine is used to optimize the RPI correlations to Site U1308, with checks to ensure compatibility with oxygen isotope records. Squared wavelet coherence (WTC) indicates significant improvement in RPI (and oxygen isotope) correlations after matching each RPI record to Site U1308, particularly for periods > 10 kyr. The level of coherence for the Atlantic RPI records and the lower resolution Pacific record implies synchronous global variability (at scales > 10 kyr) that can be attributed to the axial dipole geomagnetic field.

Published
2008
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28. Variations of the ACC-CDW during MIS3 traced by magnetic grain deposition in midlatitude South Indian Ocean cores: Connections with the northern hemisphere and with central Antarctica

Author

Carlo Laj, Marie-Alexandrine Sicre, E. Michel, Catherine Kissel, Alain Mazaud, and Jean-Louis Turon

Subjects
geography, Plateau, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, North Atlantic Deep Water, Northern Hemisphere, Physical oceanography, 010502 geochemistry & geophysics, 01 natural sciences, Gulf Stream, Geophysics, Oceanography, 13. Climate action, Geochemistry and Petrology, Middle latitudes, Thermohaline circulation, 14. Life underwater, Southern Hemisphere, Geology, 0105 earth and related environmental sciences
Abstract

We examine the magnetic mineral deposition in three cores located at midlatitude sites in the South Indian Ocean, in an area where sediment eroded from the Kerguelen-Crozet plateau and transported by the marine currents, principally the Antarctic Circum Current, accumulates at a high sedimentation rate. We focus on Marine Isotopic Stage 3, characterized by large climatic fluctuations at northern latitudes, and compare the obtained records to the climatic records at Byrd (Antarctica) and Summit (GISP2, Greenland) and to the North Atlantic Deep Water variations in the North Atlantic. Magnetic mineral deposition at the studied sites exhibits a profile with maxima at the time of Heinrich events H4 and H5, which suggests a strong Antarctic Circum Current when the North Atlantic Deep Water was reduced at northern latitude during these events. We show that an interhemispheric seesaw, characterized by temporary surface warmings in the southern hemisphere, is also marked by a strong Antarctic Circum Current at the time of the northern Heinrich events. The rapid Dansgaard-Oeschger oscillations evidenced in the northern records after interstadials IS12 and IS8 are not visible, suggesting a limited counterpart of these events in the midlatitude southern Indian Ocean.

Published
2007
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29. Geomagnetic Polarity Reversals

Author

Alain Mazaud, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2007
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30. Magnetostratigraphic dating of an intensification of glacial activity in the southern Italian Alps during Marine Isotope Stage 22

Author

Alain Mazaud, Giovanni Muttoni, Cesare Ravazzi, Marzia Breda, Carlo Laj, Eduardo Garzanti, Catherine Kissel, Roberta Pini, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Marine isotope stage, 010504 meteorology & atmospheric sciences, Pleistocene, Mammal biostratigraphy, Biostratigraphy, Ice ages, 010502 geochemistry & geophysics, 01 natural sciences, Paleontology, Arts and Humanities (miscellaneous), Vegetation cycles, Ice age, Glacial period, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Magnetostratigraphy, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Earth-Surface Processes, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, Po Plain, Alps, Alluvial fan, Glacier, 13. Climate action, General Earth and Planetary Sciences, Geology
Abstract

We applied magnetostratigraphy and mammal biostratigraphy to date climate-sensitive pollen cycles and lithostratigraphic units of the Pliocene–Pleistocene Leffe sedimentary succession from the Southern Alps, Italy. The Leffe section was correlated to additional sections (Casnigo, Fornaci di Ranica, and Pianengo) to construct a stratigraphic network along a common fluviatile system (the Serio River) sourced in the Southern Alps and flowing southward into the Po River Basin. We obtained a coherent scenario of climate variability for the last ∼ 2 Myr. At Leffe, lacustrine deposition commenced during the Olduvai Normal Subchron (1.94–1.78 Ma) and lasted up to a chronologic level compatible with Marine Isotope Stage (MIS) 22 (0.87 Ma). Pollen analysis revealed that climate varied cyclically from warm-temperate to cool during this time interval, but never as cold as during glacial intervals. At around MIS 22, climate cooled globally. Gravels, attributed to high-energy braided river systems fed locally by alluvial fans, prograded from the Serio River catchment area over the Leffe Basin and toward the Po Plain in response to a generalized event of vegetation withdrawal and enhanced physical erosion. At this time, Alpine valley glaciers reached their first maximum southward expansion with glacier fronts located at only ∼ 5 km upstream from Leffe.

Published
2007
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31. A 27 kyr terrestrial biomarker record in the southern Indian Ocean

Author

Laurent Labeyrie, Alain Mazaud, Jean-Louis Turon, Ullah Ezat, and Marie-Alexandrine Sicre

Subjects
010504 meteorology & atmospheric sciences, Atmospheric circulation, Last Glacial Maximum, Subtropics, 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, Oceanography, 13. Climate action, Geochemistry and Petrology, Polar vortex, Anticyclone, Paleoclimatology, Glacial period, Holocene, Geology, 0105 earth and related environmental sciences
Abstract

Terrestrial inputs were reconstructed using high molecular weight n-alkane concentrations recorded in the sub-Antarctic Indian Ocean core MD94-103 (45°35′S, 86°31′E, 3560 m) to examine regional changes in the atmospheric circulation over the last 27 kyr. This record was compared to the dust content of EPICA-Dome C ice and continental data from South Africa (e.g., pollen sequences and isotope records in speleothems) to get a comprehensive understanding of atmospheric links between low and midlatitudes of the Indian Ocean. Terrestrial n-alkanes indicate higher glacial than Holocene inputs and marked glacial oscillations. Minimum values during the Last Glacial Maximum (LGM) are consistent with colder and drier climate and presumably caused by the persistence of subtropical anticyclones over southern Africa limiting the amount of rainfall and vegetation growth. The otherwise higher glacial n-alkanes suggest a stronger influence of the tropical rainfall in southern Africa, likely associated with a contraction of the polar vortex with respect to its LGM position. During northern Heinrich events, moderate decline of n-alkanes suggests reduced rainfall over southern Africa possibly caused by weaker tropical easterly winds when, according to Stott et al. (2002), the Pacific Ocean would have experienced Super-ENSO conditions.

Published
2006
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32. A first-order correction to minimize environmental influence in sedimentary records of relative paleointensity of the geomagnetic field

Author

Alain Mazaud

Subjects
geography, Plateau, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Geophysics, 010502 geochemistry & geophysics, Residual, Geodesy, 01 natural sciences, Field (computer science), Intensity (physics), Earth's magnetic field, Geochemistry and Petrology, Middle latitudes, Coherence (signal processing), Sedimentary rock, Geology, 0105 earth and related environmental sciences
Abstract

We propose a simple method to minimize the residual environmental influence which may exist in paleointensity records obtained from sediments. It consists of adding, or subtracting, a fraction of the normalizer (κ, ARM, or IRM) to the normalized intensity record, so that the corrected record exhibits fluctuations uncorrelated with those of the normalizer. This method was tested with paleointensity records obtained from two cores taken at midlatitude in the South Indian Ocean cores, eastward of the Kerguelen plateau. For each core, correction increases the correlation between the three normalized intensity records, NRM/κ, NRM/ARM, and NRM/IRM. It also reduces the coherence between paleointensity records and bulk magnetic parameters used as normalizers. Although it has to be used with caution, this correction may improve paleointensity records by reducing nongeomagnetic influence. It can also be used to detect intervals where paleointensity may be unreliable, i.e., intervals where large differences between uncorrected and corrected records are observed, before and after correction.

Published
2006
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33. Changes in sedimentation patterns of the Nordic seas region across the mid-Pleistocene

Author

Henning A Bauch, Alain Mazaud, Ursula Röhl, Jan Peter Helmke, Leibniz Institute of Marine Sciences at the University of Kiel, University of Bremen, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Water mass, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Pleistocene, Ocean current, Geology, Glacier, Sedimentation, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Debris, Latitude, 13. Climate action, Geochemistry and Petrology, 14. Life underwater, Glacial period, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Sediment core data from a site in the central Nordic seas suggest that during the mid-Pleistocene revolution (MPR) this region has experienced a systematic change in its overall oceanographic and climatic conditions. First distinct changes occur around 1 Ma and reveal the beginning of a shift in climate periodicity from stronger 41-ka cycles towards a dominant 100-ka cyclicity. Most pronounced are the changes at the study region between about 700 and 420 ka, when parallel to the evolution of large 100-ka cycles a distinct decrease in the input of magnetic particles is observed. Also, for this interval an intensification of glacial conditions is indicated by a marked increase in the accumulation rates of ice-rafted debris (IRD) during marine isotope stages 16 and 12. The observed mid-Pleistocene changes were likely due to a gradual shift from a more zonal behavior of the coupled ocean–atmosphere system at high northern latitudes prior to the MPR to more meridionality thereafter, a shift that affected both the patterns of ocean circulation and ice drift in the Nordic seas region. Accordingly, the subsequent MPR-related changes of these two climate parameters should be responsible for the decrease in the concentration of magnetic particles at the study site after 700 ka. With the mid-Pleistocene strengthening of the Nordic heat pump the mode of deep-water production and the flow of bottom currents changed at high northern latitudes, which led to an increased export of magnetic particles from basaltic source regions around Greenland and Iceland into the subpolar North Atlantic. Consequently, less magnetic material was deposited in the Nordic seas than before the MPR when water mass exchange between the Nordic seas and the North Atlantic was more restricted. In addition, the large Late-Pleistocene expansions of glacial ice caps on the eastern margin of the Nordic seas led to a major change in the composition of IRD material in the study area, with more material originating from the Scandinavian and Barents Sea shelf regions, which ultimately caused a dilution of the magnetic signal.

Published
2005
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34. Behavior of u-channels during acquisition and demagnetization of remanence: implications for paleomagnetic and rock magnetic measurements

Author

Stefanie Ann Brachfeld, Catherine Kissel, Alain Mazaud, Carlo Laj, Montclair State University, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Montclair State University [USA] (MSU), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Magnetic measurements, Paleomagnetism, 010504 meteorology & atmospheric sciences, Physics and Astronomy (miscellaneous), Condensed matter physics, Magnetic moment, Demagnetizing field, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Astronomy and Astrophysics, Geophysics, Coercivity, 010502 geochemistry & geophysics, 01 natural sciences, Magnetization, Space and Planetary Science, Remanence, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Saturation (magnetic), Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

We have examined the effects of translation speed on the acquisition and demagnetization of remanence in u-channels. The speed at which the u-channel moves through alternating and steady fields has a significant effect on the efficiency of remanence acquisition and demagnetization. Anhysteretic remanence (ARM) acquisition and alternating field (AF) demagnetization efficiency are inversely correlated with translation speed. ARM acquisition is most efficient at a track speed of 1 cm/s, whereas at higher speeds ARM reaches an apparent saturation at low peak fields and has a soft coercivity spectrum during subsequent AF demagnetization. The dependence of magnetization (acquired or removed) on translation speed through alternating or steady fields is explained by the number of alternating field half-cycles experienced as the sample is translated through the applied field and on the alternating field decay rate. At slow translation speeds a u-channel experiences a comparable number of alternating field cycles to that experienced by a stationary discrete sample. At fast translation speeds, the u-channel experiences a factor of 100 fewer alternating field cycles, and the conditions experienced by the u-channel sample can be comparable to the natural reorganization time of the magnetic moments within the sediment particles during remanence acquisition and demagnetization. At low decay rates the sample has more time in the blocking field and thus a more complete approach to equilibrium.

Published
2004
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35. Evidence for a mid-Pleistocene shift of ice-drift pattern in the Nordic seas

Author

Henning A. Bauch, Jan P. Helmke, Alain Mazaud, Helmholtz Centre for Ocean Research [Kiel] (GEOMAR), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010506 paleontology, Provenance, 010504 meteorology & atmospheric sciences, Gradual transition, Pleistocene, Climate shift, Northern Hemisphere, Paleontology, 01 natural sciences, Proxy (climate), Oceanography, Arts and Humanities (miscellaneous), 13. Climate action, Earth and Planetary Sciences (miscellaneous), Nordic Seas, 14. Life underwater, Ice drift, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Sediment proxy records from a continuous, 1.5 million year long deep-sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid-Pleistocene Revolution (MPR). Red-green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid-Pleistocene climate shift was accompanied by a general change in ice-drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses.

Published
2003
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37. Geomagnetic-assisted stratigraphy and sea surface temperature changes in core MD94-103 (Southern Indian Ocean): possible implications for North-South climatic relationships around H4

Author

E. Michel, Carlo Laj, Marie-Alexandrine Sicre, Jean-Jacques Pichon, Alain Mazaud, Ullah Ezat, Luc Beaufort, Jean-Louis Turon, Catherine Kissel, Josette Duprat, Climat et Magnétisme (CLIMAG), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Collège de France (CdF)-Institut national des sciences de l'Univers (INSU - CNRS)-Aix Marseille Université (AMU)-Institut National de la Recherche Agronomique (INRA), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), and Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Collège de France (CdF (institution))-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA)

Subjects
010504 meteorology & atmospheric sciences, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, 010502 geochemistry & geophysics, 01 natural sciences, Latitude, Foraminifera, Geochemistry and Petrology, sea-surface temperature, Earth and Planetary Sciences (miscellaneous), 14. Life underwater, climate, 0105 earth and related environmental sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, biology, temperature, 15. Life on land, biology.organism_classification, Salinity, Sea surface temperature, Geophysics, Earth's magnetic field, Oceanography, Diatom, Stratigraphy, 13. Climate action, Space and Planetary Science, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Climatology, correlation, Thermohaline circulation, magnetic properties, [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology, Geology
Abstract

International audience; New records of past sea surface temperatures (SSTs) were derived in the 30-50 kyr B.P. time interval from a core located at 45degreesS in the Southern Indian Ocean, MD94-103. To investigate the climatic phasing between the Southern Indian Ocean, the Greenland and the Antarctic ice, the magnetic signal of core MD94-103 was synchronized at better than millennial accuracy in the vicinity of the Laschamp geomagnetic to a reference record, NAPIS-75, already placed on the GISP2 age model. Coccolithophorid and diatom species abundances both point to a cooling of surface waters during H4. Specific diatoms also indicate lower salinity waters during the same time interval. These observations do not support the idea that the South hemisphere warmed 1.5-2 kyr before the North hemisphere (Nature 394 (1998) 739). Rather, alkenone-derived SSTs suggest that cold conditions have characterized the surface waters in the south latitudes during H4 and H5, and that temperature at evaporation sites contributed to the isotopic events A1 and A2 visible in the isotopic records of central Antarctica (Earth Planet. Sci. Lett. 177 (2000) 219). SSTs obtained from foraminifera assemblages depict somewhat different temperature patterns, possibly indicative of water stratification. (C) 2002 Elsevier Science B.V. All rights reserved.

Published
2002
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38. Geomagnetic excursions and paleointensities in the Matuyama Chron at Ocean Drilling Program Sites 983 and 984 (Iceland Basin)

Author

Maureen E. Raymo, P Sullivan, Alain Mazaud, S Turner, James E T Channell, University of Florida [Gainesville] (UF), Climat et Magnétisme (CLIMAG), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Department of Environmental, Earth and Ocean Sciences [Boston] (EEOS), University of Massachusetts [Boston] (UMass Boston), University of Massachusetts System (UMASS)-University of Massachusetts System (UMASS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Magnetic declination, Atmospheric Science, Paleomagnetism, 010504 meteorology & atmospheric sciences, Natural remanent magnetization, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Soil Science, Magnetic dip, Matuyama Chron, Aquatic Science, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Latitude, paleointensity, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Magnetostratigraphy, 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Ecology, Paleontology, Forestry, Geophysics, Earth's magnetic field, Space and Planetary Science, Polarity chron, Seismology, Geology, excursions
Abstract

[1] We report natural remanent magnetization (NRM) directions and geomagnetic paleointensity proxies for part of the Matuyama Chron (0.9–2.2 Ma interval) from two sites located on sediment drifts in the Iceland Basin. At Ocean Drilling Program Sites 983 and 984, mean sedimentation rates in the late Matuyama Chron are 15.9 and 11.5 cm kyr−1, respectively. For the older part of the record (>1.2 Ma), oxygen isotope data are too sparse to provide the sole basis for age model construction. The resemblance of the volume susceptibility record and a reference δ18O record led us to match the two records to derive the age models. This match, based on Site 983/984 susceptibility, is consistent with available Site 983/984 benthic δ18O data. Paleointensity proxies were derived from the slope of the NRM versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30–60 mT peak field range. Paleointensity lows correspond to polarity reversals at the limits of the Jaramillo, Olduvai, Cobb Mountain, and Reunion Subchrons and to seven excursions in NRM component directions. Magnetic excursions (defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator) are observed at 932, 1048, 1115, 1190–1215 (Cobb Mountain Subchron), 1255, 1472–1480, 1567–1575 (Gilsa Subchron), and 1977 ka. The results indicate that geomagnetic directional excursions, associated with paleointensity minima, are a characteristic of the Matuyama Chron and probably of polarity chrons in general.

Published
2002
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39. L'éducation musicale à l'école. Un point de vue sur la polyvalence des enseignants du premier degré

Author

Alain Mazaud and Gilles Baillat

Subjects
Education
Abstract

The teaching of music in schools often appears as a subject of minimal importance. The two surveys on professional practices of primary school teachers which the GRPPE has conducted between 1 997 and 2000 confirms this fact. In schools, music is a subject which is sometimes neglected, often delegated to outside contributors and for which institutional requirements (syllabus, instructions, hours) only constitute vague references for the teachers. However, the data collected by the GRPPE, make it possible to go further and to start perceiving the effect of the depreciation of certain subjects on the representations of primary school teachers. Thus, the status of music contributes to the blurring of the notion of professional expertise, to a considerable distancing of teachers from teaching contents and leads to an underestimate of the specific contribution of each subject to the construction of concepts. The institution seems to be willing to make some adjusments with the announcement of a plan to restore to favour the teaching of artistic subjects. Yet, the principles upon which it is based and the prospects it opens, especially in the field of teacher training, may or may not reverse the trend., L'éducation musicale en milieu scolaire apparaît souvent comme le parent pauvre de l'enseignement. Les deux enquêtes sur les pratiques professionnelles des enseignants du primaire auxquelles s'est livré le GRPPE entre 1 997 et 2000 confirment cet état de fait. À l'école, la musique est une discipline parfois occultée, souvent déléguée à des intervenants extérieurs et pour laquelle les prescriptions institutionnelles (programmes, instructions, horaires) ne constituent souvent, pour les maîtres, que de vagues références. Mais les données recueillies par le GRPPE permettent d'aller plus loin et de commencer à percevoir l'effet de la dévalorisation de certains champs disciplinaires sur les représentations des enseignants du premier degré. Ainsi, le statut de la musique contribue au brouillage de la notion d'expertise professionnelle, à une importante prise de distance des maîtres avec les contenus d'enseignement et conduit à une sous-estimation de l'apport propre de chaque discipline dans la construction des concepts. L'institution semble vouloir corriger le tir avec l'annonce d'un plan de réhabilitation des enseignements artistiques. Mais les présupposés sur lesquels il repose, et les perspectives qu'il ouvre, notamment en matière de formation des maîtres, contribueront-ils à inverser la tendance ?, Baillat Gilles, Mazaud Alain. L'éducation musicale à l'école. Un point de vue sur la polyvalence des enseignants du premier degré. In: Recherche & Formation, N°40, 2002. Les savoirs entre pratique, formation et recherche, sous la direction de Annette Gonnin-Bolo. pp. 95-120.

Published
2002

40. Deep-penetration heat flow probes raise questions about interpretations from shorter probes

Author

Francois Harmegnies, E. Michel, Ivan Vlastélic, Paul Beuzart, Daniel Aslanian, Jean-Louis Turon, Louis Géli, Raymond Le Suavé, Jean-Yves Landure, Jean Francheteau, Alain Mazaud, Jean-Jacques Pichon, Jim Cochran, Yvon Balut, Alain Normand, Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), L'Institut polaire français Paul-Emile Victor (IPEV), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Paléocéanographie (PALEOCEAN), Unité de recherche Géosciences Marines (Ifremer) (GM), UMR 5805 Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Institut national des sciences de l'Univers (INSU - CNRS), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Géosciences Marines (GM), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)

Subjects
Convection, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Advection, Aquifer, Crust, Geophysics, 010502 geochemistry & geophysics, 01 natural sciences, Deep sea, Coring, Mantle (geology), 13. Climate action, General Earth and Planetary Sciences, Bathymetry, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geomorphology, Geology, 0105 earth and related environmental sciences
Abstract

International audience; Simulation of recent northern winter climate trends by greenhouse-gas forcing, Nature, 399, 452-455,1999. Thompson, D.WJ., and J. M.Wallace,Annular modes in the extratropical circulation, Part I, month-to-month variability./ Clim., PAGES 317,320 More than 40% of the marine heat flow data collected since the early experiments of Sir Edward Bullard in 1949 were obtained using shallow penetration probes less than 5 m long [Louden and Wright, 1989] .The common belief that these data are reliable enough to model deep-seated thermal processes is sup ported by a few experiments in which heat flow measurements made in the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Pro gram (ODP) were compared to nearby surface heat flow measurements [e.g.,Hyndman etal, 1984]. However, thermal measurements made with 18-m penetrations recently collected on the northern flank of the SouthEast Indian Ridge (SEIR) bring a new perspective to this belief. In the study area, measurements of heat flow taken at the surface (0-5 m) and mea surements taken at greater depths (3-18 m) did not always concur. Investigating this lack of agreement will help address difficult ques tions about the interpretation of shallow pene tration (< 5 m) marine heat flow measurements. The data were obtained during the MD120-ANTAUS expedition carried out by R/V Marion Dufresne that was conducted from October 12 to November 7,2000 from Fremantle, Australia, to La Reunion Island.The primary objective of this cruise was to study marine heat flow vari ations along a 14-Ma isochron that parallels the SouthEast Indian Ridge (SEIR) between the Saint-Paul/Amsterdam hot spot and the Australian-Antarctic Discordance (AAD),an anomalously deep section of the Mid-Ocean Ridge that is often attributed to a mantle "cold spot." In the 1960s and 1970s, heat flow meas urements were obtained near the AAD as part of reconnaissance surveys [Von Herzen and Langseth, 1966; Langseth and Taylor, 1967; Anderson et al., 1977]. However, to interpret heat flow variations in this region of thin and patchy sediment cover, it is not only necessary to obtain more data, but to collect data that can be used to trace water circulation and dis criminate between the conductive and the convective components of the measured heat flow.To accomplish this, we collected long sediment cores, along with heat flow data to greater depths, to study the physical properties of the sediments and tentatively investigate the role of water circulation using helium isotopic ratios 3 He/ 4 He as tracers of hydrothermal activity. If water has circulated within the crust, then the 3 He/ 4 He isotopic signature is expected to be that of the crust and upper mantle; if water circulation has been confined to the sediment layer, it is expected to be that of the ocean and atmosphere. Despite rough weather and bad seas, a total of 25 thermal measurements was obtained using 9 autonomous digital temperature probes fitted on an 18-m-long, 13-cm-diameter gravity corer.Full penetration of 18 m was regularly achieved. Figure 2 shows examples of non-linear temperature gradients obtained at three differ ent sites. Each temperature measurement was systematically duplicated by two sensors that were spaced 64 mm apart. Hence, experimen tal effects cannot explain the observed non-linearity Tests performed onboard after recovery clearly preclude systematic errors due to prob lems with calibration or drift of a thermistor. The observed non-linearity, which is too important to be explained by variations in thermal conductivity, clearly results from the combination of two natural effects: vertical advection of water into the sediments and vari ations in bottom-water temperature. Advection of water affects the shape of the temperature versus depth curve: convex curvature indicates water flowing upward; concave curvature indi cates water flowing downward; a vertical gradi ent indicates the presence of an aquifer [e.g., Anderson et al., 1979]. Yearly variations in bot tom-water temperature affect the thermal gra dient in the first 3-4 m. Although further analysis is needed to determine the characteristics of the suspected bottom-water temperature changes, our results raise questions about the heat flow estimates that we would have obtained in this specific study area using shallow penetration probes of less than ~5 m. The above describes some advantages of combining coring and heat flow measurements within the sediments at great depths. R/V Marion Dufresne has the ability to take ultra-long cores of up to 60 m using a giant corer. Fig. 1. Temperature probes welded onto the gravity corer onboard R/V Marion Dufresne. Inset shows sketch of the autonomous temperature probe. R/V Marion Dufresne is a multipurpose , 130-m-long research and supply vessel that both provides logistics for the French austral islands and conducts oceanographic research. Specifically designed for very severe weather conditions, the ship allows full performance in rough seas. The vessel, which is equipped with the full suite of geophysical facilities, including a system for multi-beam bathymetry and imagery, can raise 60-m sediment cores. Facing an increasing scientific demand, the French government decided in 1999 to reduce the ship time devoted to logistical operations to 120 days per year and allow the French Polar Institute (IFRTP) to conduct research throughout the world for 245 days per year. This paves the road for new approaches and the development of integrated, multidisciplinary programs, as recently evidenced with the MD120-ANTAUS expedition.

Published
2001
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41. Short fluctuations in Antarctic isotope records: a link with cold events in the North Atlantic?

Author

Alain Mazaud, Jean Jouzel, Françoise Vimeux, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Climat et Magnétisme (CLIMAG), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Ice stream, European Project for Ice Coring in Antarctica, Antarctic sea ice, 010502 geochemistry & geophysics, 01 natural sciences, Ice-sheet model, Geophysics, Oceanography, Ice cap climate, Ice core, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, Climatology, Earth and Planetary Sciences (miscellaneous), Cryosphere, Ice sheet, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

The recent synchronization of Antarctic and Greenland ice cores obtained by Blunier and colleagues from methane measurements in the 10–15 kyr and 25–45 kyr intervals allows us to investigate leads and lags between climatic changes in the two hemispheres. We observe that most of the cold episodes recorded in the Greenland ice correspond to peaks in isotope Antarctic records once the common timescale derived from methane measurements is adopted. These Antarctic peaks are commonly interpreted as reflecting warmings in Antarctica. Here we draw attention on a possible alternative explanation. Those peaks could, at least partially, correspond to a temporary cooling of the source water providing Antarctic precipitation as a result of cold conditions in the North Atlantic, and of a fast interhemispheric transfer of this cooling via the atmosphere or the ocean. This suggestion would be consistent with recent measurements of the deuterium excess in Vostok ice (Antarctica). Although there are good arguments in favor of the currently accepted interpretation, the influence of temperature changes in the source regions of Antarctic precipitation on the temperature proxy has to be kept in mind when interpreting the phasing between Greenland and Antarctic ice core records.

Published
2000
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42. Correlation of Marine 14 C Ages from the Nordic Seas with the GISP2 Isotope Record: Implications for 14 C Calibration Beyond 25 ka BP

Author

Alain Mazaud, Markus Schleicher, Helmut Erlenkeuser, Marie-Josée Nadeau, Michael Sarnthein, Carlo Laj, Pieter Meiert Grootes, Antje H L Voelker, Geologisch-Palaontologisches Institut, Leibniz-Labor für Altersbestimmung und Isotopenforschung, Christian-Albrechts-Universität zu Kiel (CAU), Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010506 paleontology, Archeology, 010504 meteorology & atmospheric sciences, Pleistocene, Stable isotope ratio, 01 natural sciences, Paleoatmosphere, Paleontology, Earth's magnetic field, Ice core, 13. Climate action, Absolute dating, General Earth and Planetary Sciences, 14. Life underwater, Stadial, Meltwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

We present two new high-resolution sediment records from the southwestern Iceland and Norwegian Seas that were dated by numerous 14C ages up to 54 14C ka bp. Based on various lines of evidence, the local 14C reservoir effect was restricted to 400–1600 yr. The planktic stable isotope records reveal several meltwater spikes that were sampled with an average time resolution of 50 yr in PS2644 and 130 yr in core 23071 during isotope stage 3. Most of the δ18O spikes correlate peak-by-peak to the stadials and cold rebounds of the Dansgaard-Oeschger cycles in the annual-layer counted GISP2 ice core, with the major spikes reflecting the Heinrich events 1–6. This correlation indicates large fluctuations in the calibration of 14C ages between 20 and 54 14C ka bp. Generally the results confirm the 14C age shifts as predicted by the geomagnetic model of Laj, Mazaud and Duplessy (1996). However, the amplitude and speed of the abrupt decrease and subsequent major increase of our 14C shifts after 45 14C ka bp clearly exceed the geomagnetic prediction near 40–43 and 32–34 calendar (cal) ka bp. At these times, the geomagnetic field intensity minima linked to the Laschamp and the Mono Lake excursions and confirmed by a local geomagnetic record, probably led to a sudden increase in cosmogenic 14C and 10Be production, giving rise to excess 14C in the atmosphere of up to 1200%.

Published
1998
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43. Erratum to 'Mid-latitude Southern Indian Ocean response to Northern Hemisphere Heinrich events' [Earth Planet. Sci. Lett. 240 (2005) 724-731]

Author

Sabine Schmidt, Josette Duprat, Laurent Labeyrie, Jean Louis Turon, Elisabeth Michel, Alain Mazaud, Ullah Ezat, and Marie-Alexandrine Sicre

Subjects
Indian ocean, Geophysics, Oceanography, Space and Planetary Science, Geochemistry and Petrology, Planet, Climatology, Middle latitudes, Earth and Planetary Sciences (miscellaneous), Northern Hemisphere, Earth (chemistry), Geology
Published
2006
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44. ‘Sawtooth’ variation in magnetic intensity profiles and delayed acquisition of magnetization in deep sea cores

Author

Alain Mazaud, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Natural remanent magnetization, Geophysics, Sawtooth wave, Geomagnetic reversal, Magnetization, Space and Planetary Science, Geochemistry and Petrology, hemic and lymphatic diseases, Dynamo theory, Earth and Planetary Sciences (miscellaneous), [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Deposition (chemistry), Intensity (heat transfer), Geology, ComputingMilieux_MISCELLANEOUS
Abstract

Recent records of normalised intensity of natural remanent magnetization (NRM) obtained from deep-sea sediments document an asymmetrical saw-tooth pattern, associated with geomagnetic reversals. This observation may reflect a fundamental aspect of the geodynamo time evolution or, alternatively, delay in acquisition of the NRM. It is demonstrated here that a simple model, in which a large fraction of the magnetic grains acquire NRM at deposition time while remaining grains reorientate or acquire magnetization after deposition, is able to produce a ‘saw-tooth’ profile strikingly similar to that observed. Interestingly, this mechanism of NRM acquisition does not damp out high frequency oscillations of the field, such as those observed in the deep-sea records exhibiting the saw-tooth profile. It provides an accurate record of field directions, except for periods of very low field intensity.

Published
1996
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45. An attempt at reconstructing the geomagnetic field at the core-mantle boundary during the Upper Olduvai polarity transition (1.66 Myear)

Author

Alain Mazaud, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Polarity reversal, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Physics and Astronomy (miscellaneous), Magnetic energy, Cosmic microwave background, Astronomy and Astrophysics, Geomagnetic pole, Geophysics, Geodesy, Mantle (geology), Physics::Geophysics, Earth's magnetic field, Space and Planetary Science, Core–mantle boundary, Dynamo theory, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS
Abstract

The palaeomagnetic directions of five published records obtained from sedimentary sections from various parts of the world were used to calculate maps of the radial field at the core-mantle boundary (CMB) during the Upper Olduvai polarity reversal, dated at 1.66 Myear. The five records were synchronized assuming that major changes in field direction occurred simultaneously at the five sites at the beginning and the end of the polarity transition. Low-order coefficients of the field were determined, using the hypothesis that the magnetic energy remained constant during the transition. Maps of the radial field at the CMB were calculated, assuming a perfectly insulating mantle. The results of this mapping exercise show a non-axisymmetric field at the CMB in the first and last stages of the transition, with strong flux moving in the longitudinal bands, evidenced as preferred ones for transitional Virtual Geomagnetic Poles (VGP) paths. Maps calculated at mid-reversal do not show a simple geometry. More palaeomagnetic records and more refined modelling techniques are desirable. However, the results are consistent with the idea that the transitional geodynamo is controlled by the thermal structure of the lower mantle.

Published
1995
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46. Normalised natural remanent magnetisation intensity during the last 240 000 years in piston cores from the central North Atlantic Ocean: geomagnetic field intensity or environmental signal?

Author

Andrew P. Roberts, Carlo Laj, Alain Mazaud, Catherine Kissel, Laurent Labeyrie, Lionel Endignoux, Robin J. Weeks, Erick Blanchard, Centre des Faibles Radioactivités, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), US Geological Survey [Seattle], United States Geological Survey [Reston] (USGS), Department of Geology [Davis], University of California [Davis] (UC Davis), and University of California (UC)-University of California (UC)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, geography, geography.geographical_feature_category, Physics and Astronomy (miscellaneous), Astronomy and Astrophysics, Geophysics, Deep sea, Sedimentary depositional environment, Earth's magnetic field, Volcano, Space and Planetary Science, Laschamp event, Sedimentary rock, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Magnetic dipole, Geology, Intensity (heat transfer), ComputingMilieux_MISCELLANEOUS
Abstract

We have examined in detail the stratigraphic variations in magnetic parameters of four cores from the North Atlantic Ocean in areas where the depositional environment has varied with climatic changes. Our objective is to assess whether normalisation of the natural remanent magnetisation (NRM) intensity can cancel the effect of climatically induced variations in magnetic mineral content and grain size and whether a reliable record of relative changes in geomagnetic field intensity can be obtained. After selecting the core sections which meet published criteria for paleointensity normalisation, we have attempted to obtain a record of the geomagnetic field intensity variations over the past 240 kyear, using both ARM and IRM as normalising factors for the NRM. The two methods yield overall similar results, except for the interval 20–30 kyear, where IRM normalisation yields a record more consistent with previous sedimentary and volcanic results, than does the more frequently employed ARM normalisation. The final intensity record docmments a picture of the dipole field moment which presents large similarities with profiles obtained from sediments deposited in different environmental conditions in various regions around the world. We observe a major low at about 42 kyear, which could correspond to the Laschamp event, a broad low in the interval 90–130 kyear, possibly connected to the Blake event, and another low at about 190 kyear, which could reflect the Biwa I event. The processes of acquisition of depositional and postdepositional remanent magnetisation and the physics of the normalising methods are still insufficiently understood. However, these results, obtained from a region characterised by complex environmental dynamics, confirm the potential of sedimentary deep sea cores for relative paleointensity determinations.

Published
1995
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47. A geomagnetic chronology for antarctic ice accumulation

Author

Carlo Laj, Michael L. Bender, Alain Mazaud, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Flux, Cosmic ray, Geophysics, Deep sea, Physics::Geophysics, Latitude, Earth's magnetic field, Ice core, General Earth and Planetary Sciences, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Physics::Atmospheric and Oceanic Physics, Geology, ComputingMilieux_MISCELLANEOUS, Chronology
Abstract

The curve of 10Be flux versus age in the Vostok ice core largely covaries with a synthetic curve calculated assuming that a large fraction of 10Be production rate is modulated by changes in the geomagnetic field intensity. With this assumption, it is also possible to derive a precise chronology for the Vostok core. This chronology is in good agreement with a very recent glaciological chronology obtained for Vostok ice core, and improves the correspondence of climate events recorded in Antarctic ice with correlative events recorded in deep sea sediments. Therefore, the idea that changes in the 10Be flux at Vostok may arise from variations in Earth's geomagnetic dipole field has to be seriously considered. This would imply that a large portion of the 10Be deposited there is derived from lower latitudes.

Published
1994
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48. Preferred Bands of Longitude for Geomagnetic Reversal VGP Paths: Implications for Reversal Mechanisms

Author

Carlo Laj, Michael D Fuller, Alain Mazaud, and Emilio Herrero-Bervera

Subjects
Earth's magnetic field, Mantle convection, Seismic tomography, Core–mantle boundary, Geophysics, Present day, Longitude, Geodesy, Mantle (geology), Geology, Geomagnetic reversal
Abstract

Different analysis of new records of recent polarity reversals and of many records published in the last years show a remarkable confinement of the transitional VGP’s to the longitudinal sector over the Americas and, to a lesser extent, over its antipode. This structure has persisted in time for at least 11 million years. The two longitudinal sectors defined by the VGP’s are of particular significance in reconstructions of the present day geomagnetic field and of fluid motions in the surface layers of the core. They are also found to coincide with anomalously fast regions in the mantle and at the core-mantle boundary documented by seismic tomography. Therefore the observed VGP paths link features of the core fluid motion to the temperature in the mantle, fluid motions in the core being driven by temperature patterns at the core mantle boundary during reversals.

Published
1993
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49. SEDIMENTARY RECORDS OF REVERSAL TRANSITIONS -MAGNETIZATION SMOOTHING ARTEFACT OR GEOMAGNETIC FIELD BEHAVIOUR?

Author

Carlo Laj, Emilio Herrero-Bervera, Michael D Fuller, Alain Mazaud, Robin J. Weeks, Centre des Faibles Radioactivités, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), University of California [Santa Barbara] (UC Santa Barbara), University of California (UC), and University of Hawaii

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Paleomagnetism, Geophysics, Sedimentary depositional environment, Magnetization, Earth's magnetic field, Remanence, General Earth and Planetary Sciences, Sedimentary rock, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Smoothing, Magnetostratigraphy, Geology
Abstract

International audience; Sedimentary records of reversals for the past 12 million years exhibit preferred longitudes of their VGP paths. This observation may be related to long term aspects of coremantle dynamics. However, it has been suggested that sedimentary VGP paths could be an artefact due to smoothing which mixes non antipodal pre-and post-transitional directions. We show here that smoothing over unrealistically long time scales is required to generate intermediate directions of magnetization which are purely mixtures of pre-and posttransifionals directions in sediments whose remanence is primarily depositional (DRM) or post-depositional remanence (PDRM). Sedimentary records of transitions showing VGP paths confined to the planes of immediately pre-and posttransitional VGPs have however been observed. These can be explained by non-axisymmetric bias in the non-reversing field [Gubbins and Bloxham, 1987; Constable, 1992], which plays a role in reversals. Therefore, provided that magnetization directions are properly cleaned to give single component directions, the preferential longitudes of reversal VGP paths will be due to field behaviour and not to an artefact of the magnetization process. If, however, mixtures of primary magnetization acquired at the time of the fonnation of the rock and secondary magnetization acquired later are measured, then artefacts will be generated.

Published
1992
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50. A Geomagnetic Calibration of the Radiocarbon Time-Scale

Author

E. Bard, Carlo Laj, Alain Mazaud, M. Arnold, Emmanuel Tric, Centre des Faibles Radioactivités, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Earth's magnetic field, Scale (ratio), Calibration (statistics), law, Radiocarbon dating, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geodesy, ComputingMilieux_MISCELLANEOUS, Geology, law.invention
Abstract

International audience

Published
1992
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