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6. Palaeoceanographic and hydrodynamic variability for the last 47kyr in the southern Gulf of Cádiz (Atlantic Moroccan margin): Sedimentary and climatic implications

Author

Vandorpe, T., Delivet, S., Blamart, D., Wienberg, C., Bassinot, F., Mienis, F., Stuut, J.-B. W., Van Rooij, D., Vandorpe, T., Delivet, S., Blamart, D., Wienberg, C., Bassinot, F., Mienis, F., Stuut, J.-B. W., and Van Rooij, D.

Abstract

X-ray fluorescence, grain-size and oxygen and carbon stable isotope measurements of a 33m long piston core, recovered from the Pen Duick drift located at the foot of the prominent Pen Duick Escarpment (Atlantic Moroccan margin), are combined to decipher past oceanographic conditions. The data indicate that, similar to the northern Gulf of Cádiz, the Azores Front exerts a major control on the palaeoclimatology of the region. Contrasting the northern Gulf of Cádiz, where Mediterranean Outflow Water is the main water mass at similar water depths, the palaeoceanography of the studied area is mostly influenced by the amount of Antarctic Intermediate Water advected from the south. The density contrast between the Antarctic Intermediate Water and the overlying North Atlantic Central Water determined the strength of the prevailing internal tides and corresponding high current speeds, which drastically impacted the sedimentary record. The most notable impact is the presence of a 7.8kyr condensed section (30.5–22.7ka bp). The formation of the Pen Duick sediment drift was not just controlled by the strength of the bottom currents and the intensity of the internal tides, but also by the amount of (aeolian) sediment supplied to the region. Although variable, drift-growth phases seem to mainly occur during colder periods of the last glacial, that is Heinrich and Dansgaard-Oeschger events during Marine Isotope Stage 3 and late Marine Isotope Stage 2. These periods, characterised by increased aeolian dust supply and higher bottom currents, coincide with a phase of prolific cold-water coral growth and enhanced coral mound formation as recorded in numerous cores obtained from the southern Gulf of Cádiz. This implies that both records (on and off mound cores) are pivotal to provide the complete picture of the palaeoclimatic and palaeoceanographic conditions in the region.

Published
2023

7. Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives

Author

Govin, A., Capron, E., Tzedakis, P.C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, C., St-Onge, G., Stoner, J.S., Bassinot, F., Bazin, L., Blunier, T., Combourieu-Nebout, N., El Ouahabi, A., Genty, D., Gersonde, R., Jimenez-Amat, P., Landais, A., Martrat, B., Masson-Delmotte, V., Parrenin, F., Seidenkrantz, M.-S., Veres, D., Waelbroeck, C., and Zahn, R.

Published
2015
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9. Palaeoceanographic and hydrodynamic variability for the last 47 kyr in the southern Gulf of Cádiz (Atlantic Moroccan margin): Sedimentary and climatic implications

Author

Vandorpe, T., Delivet, S., Blamart, D., Wienberg, C., Bassinot, F., Mienis, F., Stuut, J.-B.W., Van Rooij, D., Vandorpe, T., Delivet, S., Blamart, D., Wienberg, C., Bassinot, F., Mienis, F., Stuut, J.-B.W., and Van Rooij, D.

Abstract

X-ray fluorescence, grain-size and oxygen and carbon stable isotope measurements of a 33 m long piston core, recovered from the Pen Duick drift located at the foot of the prominent Pen Duick Escarpment (Atlantic Moroccan margin), are combined to decipher past oceanographic conditions. The data indicate that, similar to the northern Gulf of Cádiz, the Azores Front exerts a major control on the palaeoclimatology of the region. Contrasting the northern Gulf of Cádiz, where Mediterranean Outflow Water is the main water mass at similar water depths, the palaeoceanography of the studied area is mostly influenced by the amount of Antarctic Intermediate Water advected from the south. The density contrast between the Antarctic Intermediate Water and the overlying North Atlantic Central Water determined the strength of the prevailing internal tides and corresponding high current speeds, which drastically impacted the sedimentary record. The most notable impact is the presence of a 7.8 kyr condensed section (30.5–22.7 ka bp). The formation of the Pen Duick sediment drift was not just controlled by the strength of the bottom currents and the intensity of the internal tides, but also by the amount of (aeolian) sediment supplied to the region. Although variable, drift-growth phases seem to mainly occur during colder periods of the last glacial, that is Heinrich and Dansgaard-Oeschger events during Marine Isotope Stage 3 and late Marine Isotope Stage 2. These periods, characterised by increased aeolian dust supply and higher bottom currents, coincide with a phase of prolific cold-water coral growth and enhanced coral mound formation as recorded in numerous cores obtained from the southern Gulf of Cádiz. This implies that both records (on and off mound cores) are pivotal to provide the complete picture of the palaeoclimatic and palaeoceanographic conditions in the region.

Published
2022

16. A 5.3‐million‐year history of monsoonal precipitation in northwestern Australia

Author

Stuut, J.-B.W., De Deckker, P., Saavedra-Pellitero, M., Bassinot, F., Drury, A.-J., Walczak, M.H., Nagashima, K., Murayama, M., Stuut, J.-B.W., De Deckker, P., Saavedra-Pellitero, M., Bassinot, F., Drury, A.-J., Walczak, M.H., Nagashima, K., and Murayama, M.

Abstract

New proxy records from deep‐sea sediment cores from the northwestern continental margin of Western Australian reveal a 5.3 million year (Ma) history of aridity and tropical monsoon activity in northwestern Australia. Following the warm and dry early Pliocene (~5.3 Ma), the northwestern Australian continent experienced a gradual increase in humidity peaking at about 3.8 Ma with higher than present‐day rainfall. Between 3.8 and about 2.8 Ma, climate became progressively more arid with more rainfall variability. Coinciding with the onset of the Northern Hemisphere glaciations and the intensification of the Northern Hemisphere monsoon, aridity continued to increase overall from 2.8 Ma until today, with greater variance in precipitation and an increased frequency of large rainfall events. We associate the observed large‐scale fluctuations in Australian aridity with variations in Indian Ocean sea surface temperatures, which largely control the monsoonal precipitation in northwestern Australia.

Published
2019

19. Seismic Stratigraphy of the Ontong Java Plateau

Author

Mosher, D.C., primary, Mayer, L.A., additional, Shipley, T.H., additional, Winterer, E.L., additional, Hagen, R.A., additional, Marsters, J.C., additional, Bassinot, F., additional, Wilkens, R.H., additional, and Lyle, M., additional

Published
1993
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21. Duration and dynamics of the best orbital analogue to the present interglacial

Author

Giaccio B.[1], Regattieri E.[1, 2, Zanchetta G.[1, Nomade S.[4], Renne P.R.[5, Sprain C.J.[5, Drysdale R.N.[7, Tzedakis P.C.[9], Messina P.[1], Scardia G.[1, 10], Sposato A.[1], Bassinot F.[4], National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), 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), Berkeley Geochronology Center (BGC), University of Melbourne, Department of Geography, University College of London [London] (UCL), Consiglio Nazionale delle Ricerche [Roma] (CNR), 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
Geochemistry & Geophysics, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Marine isotope stage, Holocene, Ar/Ar geochronology, glacial inception, Geology, Vegetation, MIS19, Holocene, Isotopes of oxygen, Paleontology, Past orbital analogues to the present interglacial, 13. Climate action, duration of the Holocene, Interglacial, Earth Sciences, Flandrian interglacial, Glacial period, MIS19, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, Chronology
Abstract

Past orbital analogues to the current interglacial, such as Marine Isotope Stage 19c (MIS 19c, ca. 800 ka), can provide reliable reference intervals for evaluating the timing and the duration of the Holocene and factors inherent in its climatic progression. Here we present the first high-resolution paleoclimatic record for MIS 19 anchored to a high-precision 40Ar/39Ar chronology, thus fully independent of any a priori assumptions on the orbital mechanisms underlying the climatic changes. It is based on the oxygen isotope compositions of Italian lake sediments showing orbital- to millennial-scale hydrological variability over the Mediterranean between 810 and 750 ka. Our record indicates that the MIS 19c interglacial lasted 10.8 ± 3.7 k.y., comparable to the time elapsed since the onset of the Holocene, and that the orbital configuration at the time of the following glacial inception was very similar to the present one. By analogy, the current interglacial should be close to its end. However, greenhouse gas concentrations at the time of the MIS 19 glacial inception were significantly lower than those of the late Holocene, suggesting that the current interglacial could have already been prolonged by the progressive increase of the greenhouse gases since 8-6 ka, possibly due to early anthropogenic disturbance of vegetation.

Published
2015

23. Yttrium and Rare Earth Elements partitioning in seawaters from the Bay of Bengal

Author

YU, Zhaojie, Colin, Christophe, Douville, Éric, Meynadier, L., Duchamp-Alphonse, S., Sepulcre, S., Wan, S., Song, L., Wu, Qiong, XU, Zhaokai, Bassinot, F., Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-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), Géochrononologie Traceurs Archéométrie (GEOTRAC), 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 de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Key Laboratory of Marine Geology and Environment [China, Institute of Oceanology [China], State Key Laboratory of Marine Geology [Shanghai], Tongji University, Paléocéanographie (PALEOCEAN), 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), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU]Sciences of the Universe [physics]
Abstract

International audience; The dissolved yttrium (Y) and rare earth element (REE) concentrations of seawater samples collected along a north-south hydrological transect within the Bay of Bengal (BoB) have been analyzed to estimate contributions of the Ganges and Brahmaputra (G-B) river inputs to the dissolved REE distribution of the Northern Indian Ocean. Surface water masses of the BoB are characterized by Y/Ho ratios (84) intermediate between the G-B river suspended sediment (41) and water mass from the South Indian Ocean (93). Covariation of MREE (middle REE, Sm) and LREE (light REE, La) concentrations suggests that the dissolved REEs in surface waters (upper 100 m depth) of the BoB (Sm/La = 0.21) appear to derive mainly from the freshwater discharge of the G-B river system. In contrast, values obtained in the intermediate and deep waters (Sm/La = 0.14) suggest a mixing of dissolved REEs deriving from the release of G-B river suspended particles (Sm/La = 0.16) and the contribution of Antarctic Bottom Water (AABW) (Sm/La = 0.12). Consequently, we propose that MREE/MREE* ratios in the BoB waters could be an accurate proxy to trace lithogenic inputs from the G-B river system. The dissolved and particle remineralization Nd fluxes from G-B river system are calculated to constitute about 9% and 4% of the global dissolved river discharge and “boundary inputs” flux. Our estimation indicates that the massive G-B river system inputs could greatly alter the dissolved REEs distribution in the BoB and contribute to the dissolved REEs budget in the ocean.

Published
2017

24. Authigenic Be-10/Be-9 ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the Brunhes/Matuyama boundary

Author

Simon, Q., Thouveny, Nicolas, Bourles, D. L., Valet, J. P., Bassinot, F., Menabreaz, L., Guillou, V., Choy, S., and Beaufort, L.

Abstract

Geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (Be-10) production rates. Authigenic Be-10/Be-9 ratios (proxy of atmospheric Be-10 production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic Be-10/Be-9 ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. Variations of the authigenic Be-10/Be-9 ratio are analyzed and compared with the geomagnetic dipole low series reported from global RPI stacks. The largest Be-10 overproduction episodes are related to dipole field collapses (below a threshold of 2 x 1022 Am-2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant Be-10 production peaks are correlated to geomagnetic excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The Be-10-derived geomagnetic dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial-scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities.

Published
2016

27. An interactive tool for navigation within a database of water and carbon stable isotope records from natural archives

Author

Bolliet, T., primary, Brockmann, P., additional, Masson-Delmotte, V., additional, Bassinot, F., additional, Daux, V., additional, Genty, D., additional, Landais, A., additional, Lavrieux, M., additional, Michel, E., additional, Ortega, P., additional, Risi, C., additional, Roche, D. M., additional, Vimeux, F., additional, and Waelbroeck, C., additional

Published
2016
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28. Sequence of events from the onset to the demise of the Last Interglacial: evaluating strengths and limitations of chronologies used in climatic archives

Author

Govin, Aline, Capron, Emilie, Tzedakis, P. C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, Claude, St-Onge, G., Stoner, J. S., Bassinot, F., Bazin, Lucie, Blunier, T., Combourieu Nebout, N., El Quahabi, A., Genty, D., Gersonde, Rainer, Jiminez-Amat, P., Landais, Amaelle, Martrat, B., Masson-Delmotte, V., Parrenin, F., Seidenkrantz, Marit-Solveig, Veres, D., Waelbroeck, C., Zahn, R., Govin, Aline, Capron, Emilie, Tzedakis, P. C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, Claude, St-Onge, G., Stoner, J. S., Bassinot, F., Bazin, Lucie, Blunier, T., Combourieu Nebout, N., El Quahabi, A., Genty, D., Gersonde, Rainer, Jiminez-Amat, P., Landais, Amaelle, Martrat, B., Masson-Delmotte, V., Parrenin, F., Seidenkrantz, Marit-Solveig, Veres, D., Waelbroeck, C., and Zahn, R.

Published
2015

29. Duration and dynamics of the best orbital analogue to the present interglacial

Author

Giaccio, B, Giaccio, B, Regattieri, E, Zanchetta, G, Nomade, S, Renne, PR, Sprain, CJ, Drysdale, RN, Tzedakis, PC, Messina, P, Scardia, G, Sposato, A, Bassinot, F, Giaccio, B, Giaccio, B, Regattieri, E, Zanchetta, G, Nomade, S, Renne, PR, Sprain, CJ, Drysdale, RN, Tzedakis, PC, Messina, P, Scardia, G, Sposato, A, and Bassinot, F

Abstract

Past orbital analogues to the current interglacial, such as Marine Isotope Stage 19c (MIS 19c, ca. 800 ka), can provide reliable reference intervals for evaluating the timing and the duration of the Holocene and factors inherent in its climatic progression. Here we present the first high-resolution paleoclimatic record for MIS 19 anchored to a high-precision 40Ar/39Ar chronology, thus fully independent of any a priori assumptions on the orbital mechanisms underlying the climatic changes. It is based on the oxygen isotope compositions of Italian lake sediments showing orbital- to millennial-scale hydrological variability over the Mediterranean between 810 and 750 ka. Our record indicates that the MIS 19c interglacial lasted 10.8 ± 3.7 k.y., comparable to the time elapsed since the onset of the Holocene, and that the orbital configuration at the time of the following glacial inception was very similar to the present one. By analogy, the current interglacial should be close to its end. However, greenhouse gas concentrations at the time of the MIS 19 glacial inception were significantly lower than those of the late Holocene, suggesting that the current interglacial could have already been prolonged by the progressive increase of the greenhouse gases since 8-6 ka, possibly due to early anthropogenic disturbance of vegetation.

Published
2015

30. Sequence of events from the onset to the demise of the Last Interglacial:Evaluating strengths and limitations of chronologies used in climatic archives

Author

Govin, A., Capron, Emilie, Tzedakis, P. C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, C., St-Onge, G., Stoner, J. S., Bassinot, F., Bazin, L., Blunier, T., El Ouahabi, A., Combourieu-Nebout, N., Genty, D., Gersonde, R., Jimenez-Amat, P., Landais, A., Martrat, B., Masson-Delmotte, V., Parrenin, F., Seidenkrantz, M. -S., Veres, D., Waelbroeck, C., Zahn, R., Govin, A., Capron, Emilie, Tzedakis, P. C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, C., St-Onge, G., Stoner, J. S., Bassinot, F., Bazin, L., Blunier, T., El Ouahabi, A., Combourieu-Nebout, N., Genty, D., Gersonde, R., Jimenez-Amat, P., Landais, A., Martrat, B., Masson-Delmotte, V., Parrenin, F., Seidenkrantz, M. -S., Veres, D., Waelbroeck, C., and Zahn, R.

Published
2015

31. Further constraints on the diagenetic influences and salinity effect on Globigerinoides ruber (white) Mg/Ca thermometry: Implications in the Mediterranean Sea

Author

Sabbatini, A., Bassinot, F., Boussetta, S., Negri, A., Rebaubier, H., Dewilde, F., Nouet, J., Caillon, N., Morigi, C., Università Politecnica delle Marche [Ancona] (UNIVPM), 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), Université de Sfax - University of Sfax, Géosciences Paris Saclay (GEOPS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Geological Survey of Denmark and Greenland (GEUS), 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), Dpto Sc. Vita & Ambiente Ancona, GEOGLOB FSS, 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), and Department of Stratigraphy [Copenhagen]

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Components: 12, and modeling (0412, processes, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, early diagenetic calcite coating, 7 figures, 4243 Oceanography: General: Marginal and semi-enclosed seas, salinity Index Terms: 0424 Biogeosciences: Biosignatures and proxies, foraminiferal Mg/Ca, 4912 Paleoceanography: Biogeochemical cycles, 4805), 000 words, 3 tables Keywords: Mediterranean Sea, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment
Abstract

International audience; [1] We analyzed Mg/Ca ratios of the planktonic species Globigerinoides ruber (white) picked from 49 box core samples covering the whole Mediterranean Sea and 2 core tops from the Atlantic Ocean. Over the entire data set, we found no significant correlation between Mg/Ca and d 18 O-derived calcification temperatures. This lack of correlation is chiefly due to the presence of an early diagenetic, Mg-rich calcite coating, which can constitute up to 20% of the total shell calcite in the central and eastern Mediterranean basin and result in anomalously high Mg/Ca values and a high scattering. In the western Mediterranean Sea, however, G. ruber Mg/Ca scattering shows smaller amplitude and Mg-rich calcite remains under the XRD detection limit. SEM observations indicate that only a few samples are affected by trace amounts of post-mortem calcite overgrowths (most of this calcite being likely removed during the chemical cleaning for Mg/Ca analyses). Using core top sediments from the western Mediterranean Sea, we performed an empirical calibration exercise, which confirms that G. ruber Mg/Ca is not only related to temperature but it is also significantly affected by sea surface salinity. This salinity effect is not specific to high salinity environments such as the Mediterranean Sea, since it appears to be coherent with recent results obtained on Indo-Pacific and Atlantic surface sediments, which suggest that a +1 (psu) change in SSS results in a +1.7°C Mg/Ca-temperature bias. This sensitivity to salinity is significantly higher than those deduced from culture experiments. (2011), Further constraints on the diagenetic influences and salinity effect on Globigerinoides ruber (white) Mg/Ca thermometry

Published
2011

32. Diagenetic Mg-rich in Mediterranean sediments : quantification and impact on foraminiferal Mg/Ca thermometry

Author

Boussetta, S., Bassinot, F., Sabbatini, A., Caillon, N., Nouet, J., Kallel, N., Rebaubier, H., Klinkhammer, G., Labeyrie, L, 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), GEOGLOB FSS, Université de Sfax - University of Sfax, Dpto Sc. Vita & Ambiente Ancona, Università Politecnica delle Marche [Ancona] (UNIVPM), Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Unité GEOGLOB, Faculté des Sciences de Sfax, Université de Sfax - University of Sfax-Université de Sfax - University of Sfax, College of Oceanic and Atmospheric Sciences [Corvallis], and Oregon State University (OSU)

Subjects
[SDU.STU]Sciences of the Universe [physics]/Earth Sciences, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2011

33. Influence of orbital forcing and sea level changes in the sedimentation of the Timor Sea during the last 260 kyr

Author

Moreno, E., Bassinot, F., Baudin, François, Vénec-Peyré, M.T., Paléobiodiversité et paléoenvironnements, Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), 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-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de tectonique (LT), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Cergy Pontoise (UCP), and Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2008

34. Dissolution effects on the crystallography and Mg/Ca content of planktonic foraminifera Globorotalia tumida (Rotaliina) revealed by X-ray diffractometry

Author

Nouet, J., Bassinot, F., 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), 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), 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
foraminifera, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, dissolution, deconvolution, crystallinity, X-ray diffraction
Abstract

International audience; [1] Several authors suggested that the thinning, with increasing depth of deposition, of calcite X-ray diffractometry (XRD) peaks obtained on planktonic foraminifera tests resulted from the preferential removal of their poorly crystallized parts as dissolution increases. By deconvolving XRD peak (104) from Globorotalia tumida (surface sediments, Sierra Leone Rise depth transect), we show that the full width at midheight does not depend only upon crystallinity, but reflects also the chemical and structural heterogeneity of foraminifera tests, which results in closely spaced, individual (104) diffraction peaks corresponding to phases with slightly different Mg contents. G. tumida contains two calcite phases: a well crystallized, Mg-poor calcite and a poorly crystallized, Mg-richer calcite. Increasing dissolution results in the preferential removal of the Mg-richer calcite and the improvement of its crystallinity, whereas the Mg-poor calcite does not seem to be affected by dissolution between 2750 m and 4950 m of water depth on Sierra Leone Rise.

Published
2007

35. Phase lag between Intertropical Convergence Zone migration and subtropical monsoon onset over the northwestern Indian Ocean during Marine Isotopic Substage 6.5 (MIS 6.5)

Author

Malaizé, B., Joly, C., Vénec-Peyré, M.T., Bassinot, F., Caillon, N., Charlier, Karine, 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), Paléobiodiversité et paléoenvironnements, Muséum national d'Histoire naturelle (MNHN)-Université Pierre et Marie Curie - Paris 6 (UPMC)-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), 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), Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), 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
upwelling, Indian monsoon, sapropels, paleoclimatology, foraminifera, [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology, isotopes, ITCZ
Abstract

High-resolution faunal and isotopic analyses of foraminifera were performed on core MD96-2073 (10 degrees 94'N, 52 degrees 62'E, 3142 m depth), located close to Socotra Island in the upwelling area of the Somali Basin ( NW Indian Ocean). This work focuses on Marine Isotopic Stage 6.5 in order to reconstruct paleo-upwelling changes and their links with the Arabian Sea summer monsoon and the migration of the Intertropical Convergence Zone (ITCZ). Correspondence and cluster analyses of planktonic foraminiferal abundances, partly controlled by temperature and water mass productivity, together with an upwelling intensification index, show the occurrence of a strong upwelling between 176 and 165 ka. This upwelling intensification responds to a northward migration of the ITCZ. An isotopic depletion in the planktonic foraminifera delta(18)O records occurring between 180 and 167 ka is interpreted as proof of a large salinity decrease in the surface waters, probably linked to a strong input of fresh rainfall waters induced by an intense monsoon activity. The lag between the onset of upwelling intensification and the strong monsoonal impact over the same area suggests a decoupling between both phenomena. The migration of the ITCZ is influenced by obliquity and precessional forcing, while the Arabian Sea summer monsoon precipitation depends only on precessional forcing.

Published
2006

36. Trace element cartography of Globigerinoides ruber shells using particle-induced X-ray emission

Author

Gehlen, M., Bassinot, F., Beck, L., Khodja, H., 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), Modelling the Earth Response to Multiple Anthropogenic Interactions and Dynamics (MERMAID), 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), Laboratoire de mesure du carbone 14 (LMC14 - UMS 2572), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut de Radioprotection et de Sûreté Nucléaire (IRSN)-Ministère de la Culture et de la Communication (MCC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Pierre Süe (LPS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut de Chimie du CNRS (INC)-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
Mg/Ca, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, instruments and techniques, foraminifera, dissolution, trace elements, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Dissolution
Abstract

International audience; [1] Micro particle-induced X-ray emission (PIXE) is a nondestructive elemental analysis technique that can be used to map the distribution of elements with a spatial resolution of ±4 mm 2 and a penetration depth of ±2 mm in a calcite matrix. To test its potential to improve our understanding of trace element distribution in foraminifera shells, we mapped the Mg distribution across individual chambers of the planktonic species Globigerinoides ruber. G. ruber shells were picked from equatorial Atlantic surface sediments (Sierra Leone Rise). They ranged from well-preserved to heavily dissolved tests. The mapping of trace elements across test chambers made it possible to discriminate between variability inherent to the shell material and heterogeneity linked to contaminant phases. Contaminating mineral phases were characterized by high Mg concentrations (Mg/Ca = 19.7 mmol/mol) and high levels of Si, Al, and Fe. Mg/Ca values of well-preserved shells ranged from 3.9 to 4.5 mmol/mol. The Mg to Ca ratios of partially dissolved shells varied between 1.8 and 3.4 mmol/mol between outer and inner chambers. Low and homogeneous Mg/Ca values of 2.0 and 2.3 mmol/mol were determined for chambers of a severely dissolved test.

Published
2004

37. Late quaternary paleoclimatology of the western equatorial Pacific

Author

Rosenthal, Y, De Garidel-Thoron, T, Oppo, DW, Linsley, BK, Beaufort, L, Bassinot, F, Mix, A, Rutgers, The State University of New Jersey [New Brunswick] (RU), Rutgers University System (Rutgers), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), 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 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), 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
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology
Abstract

13th Annual VM Goldschmidt Conference, KURASHIKI, JAPAN, SEP 07-12, 2003; International audience; no abstract

Published
2003

38. Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

Author

Bassinot, F. C., Marzin, C., Braconnot, P., Marti, O., Mathien-blard, E., Lombard, F., Bopp, L., Bassinot, F. C., Marzin, C., Braconnot, P., Marti, O., Mathien-blard, E., Lombard, F., and Bopp, L.

Abstract

The relative abundance of Globigerinoides bulloides was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % G. bulloides records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at similar to 9 ka (boreal summer insolation maximum) and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at similar to 9 ka, and strengthened towards the present. Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the up-welling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer.

Published
2011
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39. Past dynamics of the Australian monsoon: precession, phase and links to the global monsoon concept

Author

Beaufort, L., Van Der Kaars, S., Bassinot, F. C., Moron, V., Beaufort, L., Van Der Kaars, S., Bassinot, F. C., and Moron, V.

Abstract

Past variations in the dynamics of the Australian monsoon have been estimated from multi-proxy analysis of a core retrieved in the Eastern Banda Sea. Records of coccolith and pollen assemblages, spanning the last 150 000 years, allow reconstruction of past primary production in the Banda Sea, summer moisture availability, and the length of the dry season in northern Australia and southeastern Indonesia. The amount of moisture available during the summer monsoon follows typical glacial/interglacial dynamics with a broad asymmetrical 100-kyr cycle. Primary production and length of the dry season appear to be closely related, given that they follow the precessional cycle with the same phase. This indicates their independence from ice-volume variations. The present inter-annual variability of both parameters is related to El Nino Southern Oscillation (ENSO), which modulates the Australian Winter Monsoon (AWM). The precessional pattern observed in the past dynamics of the AWM is found in ENSO and monsoon records of other regions. A marked shift in the monsoon intensity occurring during the mid Holocene during a period of constant ice volume, suggests that low latitude climatic variation precedes increases in global ice volume. This precessional pattern suggests that a common forcing mechanism underlies low latitude climate dynamics, acting specifically and synchronously on the different monsoon systems.

Published
2010
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40. Oxygen Isotope Composition of Planktonic Foraminiferal Shells over the Indian Ocean: Calibration to Modern Oceanographic Data

Author

Cayre, O., Bassinot, F., Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-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)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), 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), 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)

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010506 paleontology, 010504 meteorology & atmospheric sciences, biology, Temperature salinity diagrams, Globigerina bulloides, Plankton, biology.organism_classification, 01 natural sciences, Isotopes of oxygen, Oceanography, 13. Climate action, Geochemistry and Petrology, Satellite imagery, Seawater, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Bay, Globigerinoides, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

New 6180 values were obtained on Globigerinoides ruber, Globigerina bulloides and Neogh)boquadrina dutertrei picked in narrow size-fractions from 37 core-tops over the Indian Ocean. 8180 equilibrium values with respect to ambient seawater were calculated using recent temperature and salinity data from the Levitus Atlas and based on regional salinity-SlSo relationships established recently from measurements of water samples from the Arabian Sea and the Bay of Bengal. Equilibrium 8~So values are also calculated with annual temperature and salinity weighted by primary productivity derived from chlorophyll satellite imagery.

Published
1998

43. Trace element cartography of Globigerinoides ruber shells using particle-induced X-ray emission

Author

Gehlen, M, Bassinot, F, Beck, L, Khodja, H, Gehlen, M, Bassinot, F, Beck, L, and Khodja, H

Abstract

Micro particle-induced X-ray emission (PIXE) is a nondestructive elemental analysis technique that can be used to map the distribution of elements with a spatial resolution of +/-4 mum(2) and a penetration depth of +/-2 mum in a calcite matrix. To test its potential to improve our understanding of trace element distribution in foraminifera shells, we mapped the Mg distribution across individual chambers of the planktonic species Globigerinoides ruber. G. ruber shells were picked from equatorial Atlantic surface sediments (Sierra Leone Rise). They ranged from well-preserved to heavily dissolved tests. The mapping of trace elements across test chambers made it possible to discriminate between variability inherent to the shell material and heterogeneity linked to contaminant phases. Contaminating mineral phases were characterized by high Mg concentrations (Mg/Ca = 19.7 mmol/mol) and high levels of Si, Al, and Fe. Mg/Ca values of well-preserved shells ranged from 3.9 to 4.5 mmol/mol. The Mg to Ca ratios of partially dissolved shells varied between 1.8 and 3.4 mmol/mol between outer and inner chambers. Low and homogeneous Mg/Ca values of 2.0 and 2.3 mmol/mol were determined for chambers of a severely dissolved test.

Published
2004
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44. Oversampling of sedimentary series collected by giant piston corer: Evidence and corrections based on 3.5-kHz chirp profiles

Author

Szeremeta, N, Bassinot, F, Balut, Y, Labeyrie, L, Pagel, M, Szeremeta, N, Bassinot, F, Balut, Y, Labeyrie, L, and Pagel, M

Abstract

The depth-scale accuracy of marine sedimentary series collected by coring is of key importance for the precise calculation of sedimentation rates and fluxes. For three giant piston cores collected during the InterPole MD99-114/International Marine Past Global Changes Study (IMAGES) V cruise (MD99-2227, MD99-2246, and MD99-2251), the 3.5-kHz chirp profiles recorded on board are compared to synthetic seismograms computed from physical property logs measured on cores. In each case, the perfect match of main deep reflectors requires a significant upward shift of the water-sediment (W/S) interface in the synthetic seismograms with respect to the 3.5-kHz profiles. Since no drastic perturbation of the physical property logs is observed, this upward shift is interpreted as resulting from a significant sediment oversampling in the upper part of the cores. The affected depth intervals are consistent with the thickness of the perturbed zones observed in penetrometry and anisotropy of magnetic susceptibility records (similar to10-15 m). To retrieve the true in situ sediment thickness, a linear depth correction is applied between consecutive acoustic reflectors to achieve a perfect match between the synthetic seismogram and the corresponding 3.5-kHz profiles. Depth correction laws ( amount of material excess as a function of initial depth) are deduced from this resynchronization procedure. First estimations of upper core oversampling rates range from 30% (core MD99-2227) to 37% (core MD99-2246). Moreover, we observe that some undersampling may also exist in the lower part of the sediment cores.

Published
2004
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45. Evidence for large methane releases to the atmosphere from deep-sea gas-hydrate dissociation during the last glacial episode

Author

De Garidel-thoron, T, Beaufort, L, Bassinot, F, Henry, P, De Garidel-thoron, T, Beaufort, L, Bassinot, F, and Henry, P

Abstract

Past atmospheric methane-concentration oscillations recorded in polar ice cores vary together with rapid global climatic changes during the last glacial episode. In the "clathrate gun hypothesis," massive releases of deep-sea methane from marine gas-hydrate dissociation led to these well known, global, abrupt warmings in the past. If evidence for such releases in the water column exists, however, the mechanism and eventual transfer to the atmosphere has not yet been documented clearly. Here we describe a high-resolution marine-sediment record of stable carbon isotopic changes from the Papua Gulf, off Papua New Guinea, which exhibits two extremely depleted excursions (down to -9parts per thousand) at approximate to39,000 and approximate to55,000 years. Morphological, isotopic, and trace metal evidence dismisses authigenic calcite as the main source of depleted carbon. Massive methane release associated with deep-sea gas-hydrate dissociation is the most likely cause for such large depletions of delta(13)C. The absence of a delta(13)C gradient in the water column during these events implies that the methane rose through the entire water column, reaching the sea-air interface and thus the atmosphere. Foraminiferal delta(18)O composition suggests that the rise of the methane in the water column created an upwelling flow. These inferred emission events suggest that during the last glacial episode, this process was likely widespread, including tropical regions. Thus, the release of methane from the ocean floor into the atmosphere cannot be dismissed as a strong positive feedback in climate dynamics processes.

Published
2004
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