23 results on '"Bolton, Clara T."'
Search Results
2. Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean
- Author
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Adebayo, Michael B., primary, Bolton, Clara T., additional, Marchant, Ross, additional, Bassinot, Franck, additional, Conrod, Sandrine, additional, and de Garidel‐Thoron, Thibault, additional
- Published
- 2023
- Full Text
- View/download PDF
3. Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean
- Author
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Adebayo, Michael B., Bolton, Clara T., Marchant, Ross, Bassinot, Franck, Conrod, Sandrine, De Garidel‐thoron, Thibault, Adebayo, Michael B., Bolton, Clara T., Marchant, Ross, Bassinot, Franck, Conrod, Sandrine, and De Garidel‐thoron, Thibault
- Abstract
Paleoceanographic studies often rely on abundance changes in microfossil species, with little consideration for characteristics such as organism size, which may also be related to environmental changes. Using a tropical Indian Ocean (TIO) core-top data set, we test the Optimum size-hypothesis (OSH), investigating whether relative abundance or environmental variables are better descriptors of planktonic foraminifera species' optimum conditions. We also investigate the environmental drivers of whole-assemblage planktonic foraminiferal test size variation in the TIO. We use an automated imaging and sorting system (MiSo) to identify planktonic foraminiferal species, analyze their morphology, and quantify fragmentation rate using machine learning techniques. Machine model accuracy is confirmed by comparison with human classifiers (97% accuracy). Data for 33 environmental parameters were extracted from modern databases and, through exploratory factor analysis and regression models, we explore relationships between planktonic foraminiferal size and oceanographic parameters in the TIO. Results show that the size frequency distribution of most planktonic foraminifera species is unimodal, with some larger species showing multimodal distributions. Assemblage size95/5 (95th percentile size) increases with increasing species diversity, and this is attributed to vertical niche separation induced by thermal stratification. Our test for the OSH reveals that relative abundance is not a good predictor of species' optima and within-species size95/5 response to environmental parameters is species-specific, with parameters related to carbonate ion concentration, temperature, and salinity being primary drivers. At the species and assemblage levels, our analyses indicate that carbonate ion concentration and temperature play important roles in determining size trends in TIO planktonic foraminifera. Key Points Optimum size-hypothesis holds true in planktonic foraminifera if one considers th
- Published
- 2023
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4. Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene
- Author
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Bolton, Clara T., primary, Gray, Emmeline, additional, Kuhnt, Wolfgang, additional, Holbourn, Ann E., additional, Lübbers, Julia, additional, Grant, Katharine, additional, Tachikawa, Kazuyo, additional, Marino, Gianluca, additional, Rohling, Eelco J., additional, Sarr, Anta-Clarisse, additional, and Andersen, Nils, additional
- Published
- 2022
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5. Cyclic evolution of phytoplankton forced by changes in tropical seasonality
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Beaufort, Luc, primary, Bolton, Clara T., additional, Sarr, Anta-Clarisse, additional, Suchéras-Marx, Baptiste, additional, Rosenthal, Yair, additional, Donnadieu, Yannick, additional, Barbarin, Nicolas, additional, Bova, Samantha, additional, Cornuault, Pauline, additional, Gally, Yves, additional, Gray, Emmeline, additional, Mazur, Jean-Charles, additional, and Tetard, Martin, additional
- Published
- 2021
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6. Late Miocene threshold response of marine algae to carbon dioxide limitation
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Bolton, Clara T. and Stoll, Heather M.
- Subjects
Carbon dioxide -- Natural history -- Environmental aspects ,Photosynthesis -- Environmental aspects -- Natural history ,Marine algae -- Natural history -- Environmental aspects ,Coccoliths -- Natural history -- Environmental aspects ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
New measurements of stable isotope vital effects in fossil coccoliths show a step increase in reliance of coccolithophore photosynthesis on active transport of dissolved bicarbonate in the late Miocene epoch, suggesting both a low threshold for adaptation of coccolithophores to carbon dioxide and a decrease in global carbon dioxide levels at that time. Phytoplankton cell size tracks atmospheric CO.sub.2 Coccolithophores, widely distributed in the marine plankton, are unique among algae in that they use carbon for both calcification and photosynthesis. In this study Clara Bolton and Heather Stoll use a model of cellular carbon fluxes to show that when carbon dioxide concentrations are low, these organisms will allocate carbon preferentially to photosynthesis rather than to calcification, particularly in larger cells. This is reflected in a difference between the isotopic signature of small and large coccoliths that diminishes at high levels of carbon dioxide. This pattern can be seen in the fossil record; the authors identify an isotopic divergence between small and large coccoliths at around 6 million years ago, and interpret this as a threshold response of the cells' carbon acquisition to a global decrease in carbon dioxide concentrations at the time. Coccolithophores are marine algae that use carbon for calcification and photosynthesis. The long-term adaptation of these and other marine algae to decreasing carbon dioxide levels during the Cenozoic era.sup.1 has resulted in modern algae capable of actively enhancing carbon dioxide at the site of photosynthesis. This enhancement occurs through the transport of dissolved bicarbonate (HCO.sub.3.sup.-) and with the help of enzymes whose expression can be modulated by variable aqueous carbon dioxide concentration, [CO.sub.2], in laboratory cultures.sup.2,3. Coccolithophores preserve the geological history of this adaptation because the stable carbon and oxygen isotopic compositions of their calcite plates (coccoliths), which are preserved in the fossil record, are sensitive to active carbon uptake and transport by the cell. Here we use a model of cellular carbon fluxes and show that at low [CO.sub.2] the increased demand for HCO.sub.3.sup.- at the site of photosynthesis results in a diminished allocation of HCO.sub.3.sup.- to calcification, which is most pronounced in larger cells. This results in a large divergence between the carbon isotopic compositions of small versus large coccoliths only at low [CO.sub.2]. Our evaluation of the oxygen and carbon isotope record of size-separated fossil coccoliths reveals that this isotopic divergence first arose during the late Miocene to the earliest Pliocene epoch (about 7-5 million years ago). We interpret this to be a threshold response of the cells' carbon acquisition strategies to decreasing [CO.sub.2]. The documented coccolithophore response is synchronous with a global shift in terrestrial vegetation distribution between 8 and 5 Myr ago, which has been interpreted by some studies as a floral response to decreasing partial pressures of carbon dioxide ([Formula omitted]) in the atmosphere.sup.4,5,6. We infer a global decrease in carbon dioxide levels for this time interval that has not yet been identified in the sparse [Formula omitted] proxy record.sup.7 but is synchronous with global cooling and progressive glaciations.sup.8,9., Author(s): Clara T. Bolton [sup.1] , Heather M. Stoll [sup.1] Author Affiliations: (1) Geology Department, University of Oviedo, Jesus Arias de Velasco S/N, 33005, Oviedo, Asturias, Spain, Main Coccolithophores are [...]
- Published
- 2013
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7. Evidence of a South Asian proto-monsoon during the Oligocene-Miocene transition
- Author
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Beasley, Charlotte, Kender, Sev, Giosan, Liviu, Bolton, Clara T., Anand, Pallavi, Leng, Melanie J., Nilsson-Kerr, Katrina, Ullmann, Clemens Vinzenz, Hesselbo, Stephen P., Littler, Kate, Beasley, Charlotte, Kender, Sev, Giosan, Liviu, Bolton, Clara T., Anand, Pallavi, Leng, Melanie J., Nilsson-Kerr, Katrina, Ullmann, Clemens Vinzenz, Hesselbo, Stephen P., and Littler, Kate
- Abstract
The geological history of the South Asian monsoon (SAM) before the Pleistocene is not well-constrained, primarily due to a lack of available continuous sediment archives. Previous studies have noted an intensification of SAM precipitation and atmospheric circulation during the middle Miocene (∼14 Ma), but no records are available to test how the monsoon changed prior to this. In order to improve our understanding of monsoonal evolution, geochemical and sedimentological data were generated for the Oligocene-early Miocene (30–20 Ma) from Indian National Gas Hydrate Expedition 01 Site NGHP-01-01A in the eastern Arabian Sea, at 2,674 m water depth. We find the initial glaciation phase (23.7–23.0 Ma) of the Oligocene-Miocene transition (OMT) to be associated with an increase in water column ventilation and water mass mixing, suggesting an increase in winter monsoon type atmospheric circulation, possibly driven by a relative southward shift of the intertropical convergence zone. During the latter part of the OMT, or “deglaciation” phase (23.0–22.7 Ma), a long-term decrease in Mn (suggestive of deoxygenation), increase in Ti/Ca and dissolution of the biogenic carbonate fraction suggest an intensification of a proto-summer SAM system, characterized by the formation of an oxygen minimum zone in the eastern Arabian Sea and a relative increase of terrigenous material delivered by runoff to the site. With no evidence at this site for an active SAM prior to the OMT we suggest that changes in orbital parameters, as well as possibly changing Tethyan/Himalayan tectonics, caused this step change in the proto-monsoon system at this intermediate-depth site.
- Published
- 2021
8. Eocene global warming events driven by ventilation of oceanic dissolved organic carbon
- Author
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Sexton, Philip F., Norris, Richard D., Wilson, Paul A., Palike, Heiko, Westerhold, Thomas, Rohl, Ursula, Bolton, Clara T., and Gibbs, Samantha
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Global warming -- Research -- Environmental aspects ,Atmospheric carbon dioxide -- Environmental aspects -- Research ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
'Hyperthermals' are intervals of rapid, pronounced global warming known from six episodes within the Palaeocene and Eocene epochs (~65-34 million years (Myr) ago) (1-13). The most extreme hyperthermal was the [...]
- Published
- 2011
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9. Cyclic evolution of phytoplankton forced by changes in tropical seasonality
- Author
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Beaufort, Luc, Bolton, Clara T, Sarr, Anta-clarisse, Sucheras-marx, Baptiste, Rosenthal, Yair, Donnadieu, Yannick, Barbarin, Nicholas, Bova, Samantha, Cornuault, Pauline, Gally, Yves, Gray, Emmeline, Mazur, Jean-charles, Tetard, Martin, Beaufort, Luc, Bolton, Clara T, Sarr, Anta-clarisse, Sucheras-marx, Baptiste, Rosenthal, Yair, Donnadieu, Yannick, Barbarin, Nicholas, Bova, Samantha, Cornuault, Pauline, Gally, Yves, Gray, Emmeline, Mazur, Jean-charles, and Tetard, Martin
- Abstract
The effect of global climate cycles driven by Earth’s orbital variations on evolution is poorly understood because of difficulties achieving sufficiently-resolved records of past evolution. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable an exceptional assessment of the impact of cyclic orbital-scale climate change on evolution because of their abundance in marine sediments, and because coccolithophores demonstrate extreme morphological plasticity in response to the changing environment1,2. Recently, evolutionary genetic analyses linked broad changes in Pleistocene fossil coccolith morphology to species radiation events3. Here, using high-resolution coccolith data, we show that during the last 2.8 million years coccolithophore evolution was forced by Earth’s orbital eccentricity with rhythms of ~100,000 years and 405,000 years - a distinct spectral signature to that of coeval global climate cycles4. Simulations with an Earth System Model5 including the marine carbon cycle6 demonstrate that eccentricity directly impacts the diversity of ecological niches occurring over the annual cycle in the tropical ocean. Reduced seasonality favours species with mid-size coccoliths that bloom year-round, increasing coccolith carbonate export and burial. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year pacing seen in records of the global carbon cycle.
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- 2020
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10. Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene.
- Author
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Bolton, Clara T., Gray, Emmeline, Wolfgang Kuhnt, Holbourn, Ann E., Lübbers, Julia, Grant, Katharine, Kazuyo Tachikawa, Marino, Gianluca, Rohling, Eelco J., Sarr, Anta-Clarisse, and Andersen, Nils
- Abstract
In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record as strong variance in the precession band (19-23 kyr) because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale variability of the monsoon in the pre-Pleistocene, when atmospheric CO
2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (< 1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost Bay of Bengal spanning the late Miocene and earliest Pliocene (9 to 5 million years ago). Underpinned by a new orbitally-tuned benthic isotope stratigraphy, we use X-Ray Fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Our data show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma, with no apparent intensification over the late Miocene. [ABSTRACT FROM AUTHOR]- Published
- 2021
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11. Plio-Pleistocene glacial-interglacial productivity changes in the eastern equatorial Pacific upwelling system
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Jakob, Kim, Wilson, Paul A., Bahr, André, Bolton, Clara T., Pross, Jörg, Fiebig, Jens, Friedrich, Oliver, National Oceanography Centre [Southampton] (NOC), University of Southampton, 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), Federal Institute of Hydrology (BfG), Institute of Geosciences [Frankfurt am Main], Goethe-Universität Frankfurt am Main, Universität Heidelberg [Heidelberg] = Heidelberg University, 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), Universität Heidelberg [Heidelberg], 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
[SDE.MCG]Environmental Sciences/Global Changes ,[SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience; The eastern equatorial Pacific Ocean (EEP) upwelling system supports >10% of the present-day global ocean primary production, making it an important component in Earth's atmospheric and marine carbon budget. Traditionally, it has been argued that since intensification of Northern Hemisphere glaciation (iNHG, ~2.7 Ma), changes in EEP productivity have predominantly depended on trade wind strength-controlled upwelling intensity. An alternative hypothesis suggests that EEP productivity is primarily controlled by nutrient supply from the high southern latitudes via mode waters. Here we present new high-resolution data for the latest Pliocene/early Pleistocene from Ocean Drilling Program Site 849, located within the equatorial divergence system in the heart of the EEP upwelling regime. We use carbon isotopes in benthic and planktic foraminiferal calcite and sand accumulation rates to investigate glacial-interglacial (G-IG) productivity fluctuations between 2.65 and 2.4 Ma (marine isotope stages (MIS) G1 to 94). This interval includes MIS 100, 98, and 96, three large-amplitude glacials (~1‰ in benthic δ18O) representing the culmination of iNHG. Our results suggest that latest Pliocene/early Pleistocene G-IG productivity changes in the EEP were strongly controlled by nutrient supply from Southern Ocean-sourced mode waters. Our records show a clear G-IG cyclicity from MIS 100 onward with productivity levels increasing from full glacial conditions and peaking at glacial terminations. We conclude that enhanced nutrient delivery from high southern latitudes during full glacial conditions together with superimposed intensified regional upwelling toward glacial terminations strongly regulated primary productivity rates in the EEP from MIS 100 onward.
- Published
- 2016
12. Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan
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Chang, Liao, Bolton, Clara T., Dekkers, Mark J., Hayashida, Akira, Heslop, David, Krijgsman, Wout, Kodama, Kazuto, Paterson, Greig A., Roberts, Andrew P., Rohling, Eelco J., Yamamoto, Yuhji, Zhao, Xiang, Chang, Liao, Bolton, Clara T., Dekkers, Mark J., Hayashida, Akira, Heslop, David, Krijgsman, Wout, Kodama, Kazuto, Paterson, Greig A., Roberts, Andrew P., Rohling, Eelco J., Yamamoto, Yuhji, and Zhao, Xiang
- Abstract
We have identified millennial-scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down-core magnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis; (3) down-core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asian monsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial-scale environmental modulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic-rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signals.
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- 2016
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13. Decrease in coccolithophore calcification and CO2 since the middle Miocene
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Bolton, Clara T., primary, Hernández-Sánchez, María T., additional, Fuertes, Miguel-Ángel, additional, González-Lemos, Saúl, additional, Abrevaya, Lorena, additional, Mendez-Vicente, Ana, additional, Flores, José-Abel, additional, Probert, Ian, additional, Giosan, Liviu, additional, Johnson, Joel, additional, and Stoll, Heather M., additional
- Published
- 2016
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14. Response to “Comment on ‘The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site’, by David Lang et al.”
- Author
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Lang, David C., Bailey, Ian, Wilson, Paul A., Foster, Gavin L., Bolton, Clara T., Friedrich, Oliver, Gutjahr, Marcus, Lang, David C., Bailey, Ian, Wilson, Paul A., Foster, Gavin L., Bolton, Clara T., Friedrich, Oliver, and Gutjahr, Marcus
- Published
- 2014
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15. A 500,000 year record of Indian summer monsoon dynamics recorded by eastern equatorial Indian Ocean upper water-column structure
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Bolton, Clara T., Chang, Liao, Clemens, Steven C, Kodama, Kazuto, Ikehara, Minoru, Medina-Elizalde, M, Paterson, Greig A, Roberts, Andrew, Rohling, Eelco J., Yamamoto, Yuhji, Zhao, Xiang, Bolton, Clara T., Chang, Liao, Clemens, Steven C, Kodama, Kazuto, Ikehara, Minoru, Medina-Elizalde, M, Paterson, Greig A, Roberts, Andrew, Rohling, Eelco J., Yamamoto, Yuhji, and Zhao, Xiang
- Abstract
The Indian Summer Monsoon (ISM) is an inter-hemispheric and highly variable ocean-atmosphere-land interaction that directly affects the densely populated Indian subcontinent. Here, we present new records of palaeoceanographic variability that span the las
- Published
- 2013
16. Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes
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Bretschneider, Lisa, Hathorne, Ed C., Bolton, Clara T., Gebregiorgis, Daniel, Giosan, Liviu, Gray, Emmeline, Huang, Huang, Holbourn, Ann, Kuhnt, Wolfgang, Frank, Martin, Bretschneider, Lisa, Hathorne, Ed C., Bolton, Clara T., Gebregiorgis, Daniel, Giosan, Liviu, Gray, Emmeline, Huang, Huang, Holbourn, Ann, Kuhnt, Wolfgang, and Frank, Martin
- Abstract
The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.
17. The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean
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Lübbers, Julia, Kuhnt, Wolfgang, Holbourn, Ann E., Bolton, Clara T., Gray, Emmeline, Usui, Yoichi, Kochhann, Karlos G. D., Beil, Sebastian, Andersen, Nils, Lübbers, Julia, Kuhnt, Wolfgang, Holbourn, Ann E., Bolton, Clara T., Gray, Emmeline, Usui, Yoichi, Kochhann, Karlos G. D., Beil, Sebastian, and Andersen, Nils
- Abstract
We integrate benthic foraminiferal stable isotopes, X‐ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon.
18. Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene
- Author
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Bolton, Clara T., Gray, Emmeline, Kuhnt, Wolfgang, Holbourn, Ann E., Lübbers, Julia, Grant, Katharine, Tachikawa, Kazuyo, Marino, Gianluca, Rohling, Eelco J., Sarr, Anta-Clarisse, Andersen, Nils, Bolton, Clara T., Gray, Emmeline, Kuhnt, Wolfgang, Holbourn, Ann E., Lübbers, Julia, Grant, Katharine, Tachikawa, Kazuyo, Marino, Gianluca, Rohling, Eelco J., Sarr, Anta-Clarisse, and Andersen, Nils
- Abstract
In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record in the form of strong variance in the precession band (19–23 kyr), because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale monsoon variability in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (<1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost part of the Bay of Bengal spanning the late Miocene (9 to 5 million years ago). Underpinned by a new orbitally tuned benthic isotope stratigraphy, we use X-ray fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Results show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma in the equatorial sector of the Indian Ocean, with no apparent intensification over the latest Miocene.
19. The Middle to Late Miocene “Carbonate Crash” in the Equatorial Indian Ocean
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Lübbers, Julia, Kuhnt, Wolfgang, Holbourn, Ann E., Bolton, Clara T., Gray, Emmeline, Usui, Yoichi, Kochhann, Karlos G. D., Beil, Sebastian, Andersen, Nils, Lübbers, Julia, Kuhnt, Wolfgang, Holbourn, Ann E., Bolton, Clara T., Gray, Emmeline, Usui, Yoichi, Kochhann, Karlos G. D., Beil, Sebastian, and Andersen, Nils
- Abstract
We integrate benthic foraminiferal stable isotopes, X‐ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene carbonate crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Interocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the carbonate crash. An increase in U1443 Log (Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the biogenic bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon.
20. Drivers of late Miocene tropical sea surface cooling: a new perspective from the equatorial Indian Ocean
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Martinot, Claire, Bolton, Clara T., Sarr, Anta-Clarisse, Donnadieu, Yannick, Garcia, Marta, Gray, Emmeline, Tachikawa, Kazuyo, Martinot, Claire, Bolton, Clara T., Sarr, Anta-Clarisse, Donnadieu, Yannick, Garcia, Marta, Gray, Emmeline, and Tachikawa, Kazuyo
- Abstract
During the late Miocene, global cooling occurred alongside the establishment of near-modern terrestrial and marine ecosystems. Significant (3 to 5 °C) sea surface cooling from 7.5 to 5.5 Ma is recorded by proxies at mid to high latitudes, yet the magnitude of tropical cooling and the role of atmospheric carbon dioxide (pCO2) in driving this trend are debated. Here, we present a new orbital-resolution sea surface temperature (SST) record spanning the late Miocene to earliest Pliocene (9 to 5 Ma) from the eastern equatorial Indian Ocean (International Ocean Discovery Program Site U1443) based on Mg/Ca ratios measured in tests of the planktic foraminifer Trilobatus trilobus. Our SST record reveals a 3.2 °C decrease from 7.4 to 5.8 Ma, significantly increasing previous estimates of late Miocene tropical cooling. Analysis of orbital-scale variability shows that before the onset of cooling, SST variations were dominated by precession-band (19-23 kyr) variability, whereas tropical temperature became highly sensitive to obliquity (41 kyr) after 7.5 Ma, suggesting an increase in high latitude forcing. We compare a revised global SST database with new paleoclimate model simulations and show that a pCO2 decrease from 560 ppm to 300 ppm, in the range suggested by pCO2 proxy records, could explain most of the late Miocene sea surface cooling observed at Site U1443. Using our new Site U1443 record as representative of tropical SST evolution, estimated meridional SST gradients suggest a much more modest increase over the late Miocene than previously suggested, in agreement with modelled meridional SST gradients.
21. Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene
- Author
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Bolton, Clara T., Gray, Emmeline, Kuhnt, Wolfgang, Holbourn, Ann E., Lübbers, Julia, Grant, Katharine, Tachikawa, Kazuyo, Marino, Gianluca, Rohling, Eelco J., Sarr, Anta-Clarisse, Andersen, Nils, Bolton, Clara T., Gray, Emmeline, Kuhnt, Wolfgang, Holbourn, Ann E., Lübbers, Julia, Grant, Katharine, Tachikawa, Kazuyo, Marino, Gianluca, Rohling, Eelco J., Sarr, Anta-Clarisse, and Andersen, Nils
- Abstract
In the modern northern Indian Ocean, biological productivity is intimately linked to near-surface oceanographic dynamics forced by the South Asian, or Indian, monsoon. In the late Pleistocene, this strong seasonal signal is transferred to the sedimentary record in the form of strong variance in the precession band (19–23 kyr), because precession dominates low-latitude insolation variations and drives seasonal contrast in oceanographic conditions. In addition, internal climate system feedbacks (e.g. ice-sheet albedo, carbon cycle, topography) play a key role in monsoon variability. Little is known about orbital-scale monsoon variability in the pre-Pleistocene, when atmospheric CO2 levels and global temperatures were higher. In addition, many questions remain open regarding the timing of the initiation and intensification of the South Asian monsoon during the Miocene, an interval of significant global climate change that culminated in bipolar glaciation. Here, we present new high-resolution (<1 kyr) records of export productivity and sediment accumulation from International Ocean Discovery Program Site U1443 in the southernmost part of the Bay of Bengal spanning the late Miocene (9 to 5 million years ago). Underpinned by a new orbitally tuned benthic isotope stratigraphy, we use X-ray fluorescence-derived biogenic barium variations to discern productivity trends and rhythms. Results show strong eccentricity-modulated precession-band productivity variations throughout the late Miocene, interpreted to reflect insolation forcing of summer monsoon wind strength in the equatorial Indian Ocean. On long timescales, our data support the interpretation that South Asian monsoon winds were already established by 9 Ma in the equatorial sector of the Indian Ocean, with no apparent intensification over the latest Miocene.
22. Decrease in coccolithophore calcification and CO2 since the middle Miocene.
- Author
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Bolton, Clara T., Hernández-Sánchez, María T., Fuertes, Miguel-Ángel, González-Lemos, Saúl, Abrevaya, Lorena, Mendez-Vicente, Ana, Flores, José-Abel, Probert, Ian, Giosan, Liviu, Johnson, Joel, and Stoll, Heather M.
- Published
- 2016
- Full Text
- View/download PDF
23. Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes
- Author
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Wolfgang Kuhnt, Clara T Bolton, Huang Huang, Emmeline Gray, Ed C Hathorne, Liviu Giosan, Daniel Gebregiorgis, Martin Frank, Lisa Bretschneider, Ann Holbourn, Helmholtz Centre for Ocean Research [Kiel] (GEOMAR), 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), Georgia State University, University System of Georgia (USG), Woods Hole Oceanographic Institution (WHOI), The Open University [Milton Keynes] (OU), Christian-Albrechts University of Kiel, ANR-16-CE01-0004,iMonsoon,Forçages et rétroactions de la mousson dans un climat chaud(2016), Bretschneider, Lisa, 1 GEOMAR Helmholtz Centre for Ocean Research Kiel Kiel Germany, Bolton, Clara T., 2 Aix Marseille Univ CNRS IRD INRAE Coll France CEREGE Aix‐en‐Provence France, Gebregiorgis, Daniel, 3 Department of Geosciences Georgia State University Atlanta GA USA, Giosan, Liviu, 4 Woods Hole Oceanographic Institution Falmouth MA USA, Gray, Emmeline, Huang, Huang, Holbourn, Ann, 7 Institute of Geosciences Christian‐Albrechts‐University Kiel Kiel Germany, Kuhnt, Wolfgang, and Frank, Martin
- Subjects
ddc:551.701 ,Atmospheric Science ,Provenance ,ddc:551.302 ,Radiogenic nuclide ,010504 meteorology & atmospheric sciences ,[SDE.MCG]Environmental Sciences/Global Changes ,Geochemistry ,Paleontology ,Sediment ,Weathering ,Late Miocene ,010502 geochemistry & geophysics ,Oceanography ,Monsoon ,01 natural sciences ,13. Climate action ,[SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Precipitation ,Global cooling ,Geology ,0105 earth and related environmental sciences - Abstract
The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition., Plain Language Summary: The South Asian or Indian monsoon affects the lives of billions. Through the erosion and weathering of rocks, the monsoon also has the potential to remove carbon dioxide from the atmosphere through increased weathering in the region including the Himalaya Mountains. The late Miocene, between 9 and 5 million years ago, was a period of global cooling and proliferation of grasslands in different regions including South Asia. Here, we examine the composition of clays formed by rock weathering during the late Miocene to determine their source region around the Bay of Bengal. The results suggest a generally stable mixture of sources with the strongest sources being regions with the highest monsoon rainfall today. We identify slight changes in the mixture of sources, which accompany a global change in carbon cycling, highlighting the role monsoon climate likely played in these changes. Toward the end of the Miocene, we identify a change in the Sr isotopes, which was not caused by source changes but by the strength of the rock weathering. This change has been observed in global records and it seems likely that it was driven by rock weathering in the South Asian Monsoon region., Highlights: Radiogenic isotope compositions of detrital clays from the Bay of Bengal indicate a generally stable provenance from 9 to 5 Ma. A step change in Nd and Pb isotope compositions at ∼7.3 Ma reflects a climatically driven eastward shift in precipitation patterns resulting in enhanced erosion of the Indo‐Burman Ranges. Elevated 87Sr/86Sr between 6 and 5 Ma was likely related to increased chemical weathering caused by thicker soils and by C4 plant expansion., DFG, ANR, IODP
- Published
- 2021
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