Articles | Volume 44, issue 2
https://doi.org/10.5194/jm-44-555-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/jm-44-555-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
18 Nov 2025
Research article |
| 18 Nov 2025
| 18 Nov 2025
Paleoproductivity and coccolith carbonate export in the northern Bay of Bengal during the late Pleistocene
Institute of Geology and Palaeontology, Faculty of Sciences, Charles University, Prague, Czech Republic
Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
Luc Beaufort
Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
Franck Bassinot
Laboratoire des Sciences du Climat et de l'Environnement – LSCE, Gif sur Yvette CEDEX, France
Katarína Holcová
Institute of Geology and Palaeontology, Faculty of Sciences, Charles University, Prague, Czech Republic
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Heather M. Stoll, Clara Bolton, Madalina Jaggi, Alfredo Martinez-Garcia, and Stefano M. Bernasconi
Clim. Past, 21, 2189–2203, https://doi.org/10.5194/cp-21-2189-2025, https://doi.org/10.5194/cp-21-2189-2025, 2025
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In periods of high atmospheric CO2 many proxies suggest more extreme past polar warming than is simulated by current coupled climate models. Providing new data on high latitude temperatures in the South Atlantic over the last 15 million years using clumped isotope thermometry, we show that absolute temperatures may not have been as warm as indicated by some biomarker based proxy climate records.
Anne L. Kruijt, Robin van Dijk, Olivier Sulpis, Luc Beaufort, Guillaume Lassus, Geert-Jan Brummer, A. Daniëlle van der Burg, Ben A. Cala, Yasmina Ourradi, Katja T. C. A. Peijnenburg, Matthew P. Humphreys, Sonia Chaabane, Appy Sluijs, and Jack J. Middelburg
EGUsphere, https://doi.org/10.5194/egusphere-2025-4234, https://doi.org/10.5194/egusphere-2025-4234, 2025
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We measured the three main types of plankton that produce calcium carbonate in the ocean, at the same time and location. While coccolithophores were the biggest contributors, we found that planktonic gastropods, not foraminifera, were the second largest contributor. This challenges the current view and improves our understanding of how these organisms influence oceans’ carbon cycling.
Deborah N. Tangunan, Ian R. Hall, Luc Beaufort, Melissa A. Berke, Alexandra Nederbragt, and Paul R. Bown
EGUsphere, https://doi.org/10.5194/egusphere-2025-3557, https://doi.org/10.5194/egusphere-2025-3557, 2025
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We examined ocean sediments from the tropical Indian Ocean to study water column structure and carbon cycling during the mid-Piacenzian Warm Period, about 3 million years ago, when atmospheric carbon dioxide levels were similar to today. Our findings reveal persistent upper ocean stratification and niche separation among plankton groups, which limited nutrient mixing and carbon export to the deep ocean. These results highlight how ocean layering can influence climate feedback in a warmer world.
Pauline Cornuault, Luc Beaufort, Heiko Pälike, Torsten Bickert, Karl-Heinz Baumann, and Michal Kucera
EGUsphere, https://doi.org/10.5194/egusphere-2025-198, https://doi.org/10.5194/egusphere-2025-198, 2025
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We present new high-resolution data of the relative contribution of the two main pelagic carbonate producers (coccoliths and foraminifera) to the total pelagic carbonate production from the tropical Atlantic in past warm periods since the Miocene. Our findings suggests that the two groups responded differently to orbital forcing and oceanic changes in tropical ocean, but their proportion changes did not drive the changes in overall pelagic carbonate deposition.
Luc Beaufort and Anta-Clarisse Sarr
Clim. Past, 20, 1283–1301, https://doi.org/10.5194/cp-20-1283-2024, https://doi.org/10.5194/cp-20-1283-2024, 2024
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At present, under low eccentricity, the tropical ocean experiences a limited seasonality. Based on eight climate simulations of sea surface temperature and primary production, we show that, during high-eccentricity times, significant seasons existed in the tropics due to annual changes in the Earth–Sun distance. Those tropical seasons are slowly shifting in the calendar year to be distinct from classical seasons. Their past dynamics should have influenced phenomena like ENSO and monsoons.
Celina Rebeca Valença, Luc Beaufort, Gustaaf Marinus Hallegraeff, and Marius Nils Müller
Biogeosciences, 21, 1601–1611, https://doi.org/10.5194/bg-21-1601-2024, https://doi.org/10.5194/bg-21-1601-2024, 2024
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Coccolithophores contribute to the global carbon cycle and their calcite structures (coccoliths) are used as a palaeoproxy to understand past oceanographic conditions. Here, we compared three frequently used methods to estimate coccolith mass from the model species Emiliania huxleyi and the results allow for a high level of comparability between the methods, facilitating future comparisons and consolidation of mass changes observed from ecophysiological and biogeochemical studies.
Ruifang Ma, Sophie Sépulcre, Laetitia Licari, Frédéric Haurine, Franck Bassinot, Zhaojie Yu, and Christophe Colin
Clim. Past, 18, 1757–1774, https://doi.org/10.5194/cp-18-1757-2022, https://doi.org/10.5194/cp-18-1757-2022, 2022
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We provide high-resolution Cd / Ca records of benthic foraminifera on two cores from the northern Indian Ocean since the last deglaciation. We reconstructed intermediate Cdw records based on Cd / Ca. Combined with benthic foraminiferal assemblages, we show that intermediate Cdw during the last deglaciation was mainly influenced by the ventilation of intermediate–bottom water masses. Thereafter during the Holocene surface productivity is the main forcing factor related to monsoon precipitation.
Clara T. Bolton, Emmeline Gray, Wolfgang Kuhnt, Ann E. Holbourn, Julia Lübbers, Katharine Grant, Kazuyo Tachikawa, Gianluca Marino, Eelco J. Rohling, Anta-Clarisse Sarr, and Nils Andersen
Clim. Past, 18, 713–738, https://doi.org/10.5194/cp-18-713-2022, https://doi.org/10.5194/cp-18-713-2022, 2022
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The timing of the initiation and evolution of the South Asian monsoon in the geological past is a subject of debate. Here, we present a new age model spanning the late Miocene (9 to 5 million years ago) and high-resolution records of past open-ocean biological productivity from the equatorial Indian Ocean that we interpret to reflect monsoon wind strength. Our data show no long-term intensification; however, strong orbital periodicities suggest insolation forcing of monsoon wind strength.
Camille Godbillot, Fabrice Minoletti, Franck Bassinot, and Michaël Hermoso
Clim. Past, 18, 449–464, https://doi.org/10.5194/cp-18-449-2022, https://doi.org/10.5194/cp-18-449-2022, 2022
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We test a new method to reconstruct past atmospheric CO2 levels based on the geochemistry of pelagic algal biominerals (coccoliths), which recent culture and numerical experiments have related to ambient CO2 concentrations. By comparing the isotopic composition of fossil coccoliths to the inferred surface ocean CO2 level at the time they calcified, we outline a transfer function and argue that coccolith vital effects can be used to reconstruct geological pCO2 beyond the ice core record.
Martin Tetard, Laetitia Licari, Ekaterina Ovsepyan, Kazuyo Tachikawa, and Luc Beaufort
Biogeosciences, 18, 2827–2841, https://doi.org/10.5194/bg-18-2827-2021, https://doi.org/10.5194/bg-18-2827-2021, 2021
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Oxygen minimum zones are oceanic regions almost devoid of dissolved oxygen and are currently expanding due to global warming. Investigation of their past behaviour will allow better understanding of these areas and better prediction of their future evolution. A new method to estimate past [O2] was developed based on morphometric measurements of benthic foraminifera. This method and two other approaches based on foraminifera assemblages and porosity were calibrated using 45 core tops worldwide.
Luc Beaufort, Yves Gally, Baptiste Suchéras-Marx, Patrick Ferrand, and Julien Duboisset
Biogeosciences, 18, 775–785, https://doi.org/10.5194/bg-18-775-2021, https://doi.org/10.5194/bg-18-775-2021, 2021
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The coccoliths are major contributors to the particulate inorganic carbon in the ocean. They are extremely difficult to weigh because they are too small to be manipulated. We propose a universal method to measure thickness and weight of fine calcite using polarizing microscopy that does not require fine-tuning of the light or a calibration process. This method named "bidirectional circular polarization" uses two images taken with two directions of a circular polarizer.
Martin Tetard, Ross Marchant, Giuseppe Cortese, Yves Gally, Thibault de Garidel-Thoron, and Luc Beaufort
Clim. Past, 16, 2415–2429, https://doi.org/10.5194/cp-16-2415-2020, https://doi.org/10.5194/cp-16-2415-2020, 2020
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Radiolarians are marine micro-organisms that produce a siliceous shell that is preserved in the fossil record and can be used to reconstruct past climate variability. However, their study is only possible after a time-consuming manual selection of their shells from the sediment followed by their individual identification. Thus, we develop a new fully automated workflow consisting of microscopic radiolarian image acquisition, image processing and identification using artificial intelligence.
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Short summary
The Bay of Bengal is a unique region influenced by the Asian monsoon. We present a record of past ocean productivity and carbonate flux based on the fossil remains of calcifying algae over the last 279 000 years from a core in the northern Bay of Bengal. We used AI microscopy to count and measure plankton fossils and identify species. Results show that coccolith export, including of the species Florisphaera profunda, is highest when the monsoon is weak and the water column is more mixed.
The Bay of Bengal is a unique region influenced by the Asian monsoon. We present a record of...
