Articles | Volume 23, issue 15
https://doi.org/10.5194/bg-23-5477-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-23-5477-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
10 Aug 2026
Research article |
| 10 Aug 2026
| 10 Aug 2026
Planktonic foraminifera iodine ∕ calcium ratio: is it a proxy for dissolved oxygen in the ocean?
Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France
Kazuyo Tachikawa
Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France
Marta Garcia
Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France
Giuseppe Siani
Laboratoire de Géosciences Paris-Saclay (GEOPS), CNRS, Paris Saclay, France
Marie Revel
Université de la Cote d'Azur, CNRS, OCA, IRD, Geoazur, Valbonne, France
Hartmut Schulz
Department of Geosciences, University of Tübingen, Tübingen, Germany
Francisco Sierro
Dept. de Geología, Univ. de Salamanca, Plaza de los Caídos s/n, 37008, Salamanca, Spain
Thomas Chalk
Aix Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, Aix-en-Provence, France
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Adele Westgård, Mohamed M. Ezat, Freya E. Sykes, Julie Meilland, Thomas B. Chalk, J. Andy Milton, Melissa Chierici, and Gavin L. Foster
EGUsphere, https://doi.org/10.5194/egusphere-2026-2415, https://doi.org/10.5194/egusphere-2026-2415, 2026
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We present a novel approach to reconstructing past temperatures in the polar oceans using Mg/Ca in planktic foraminifera which accounts for their geochemically distinct shell components. We extend the lab-based temperature calibration from 9 to 2 °C and show that also pH and [CO32-] influence Mg/Ca. These results may improve polar paleoclimate reconstructions. Additionally, our study shows that water conditions influence shell growth which has implications for ongoing climate change.
Sonia Chaabane, Ralf Schiebel, Julie Meilland, Geert-Jan A. Brummer, P. Graham Mortyn, Olivier Sulpis, Thomas B. Chalk, Xavier Giraud, Helene Howa, Azumi Kuroyanagi, Gregory Beaugrand, and Thibault de Garidel-Thoron
J. Micropalaeontol., 45, 195–217, https://doi.org/10.5194/jm-45-195-2026, https://doi.org/10.5194/jm-45-195-2026, 2026
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Using the FORCIS database, we mapped the distribution of planktonic goraminifera that record past ocean conditions. Our study reveals that these species mostly inhabit the upper ocean and thrive in waters ranging from −2 °C to over 31 °C. Their range is shifting, with species once limited to warm regions now appearing in cooler areas and smaller species increasing in number. This work refines our view of their biogeography and how climate change is reshaping ocean life.
Babette A.A. Hoogakker, Catherine Davis, Yi Wang, Stephanie Kusch, Katrina Nilsson-Kerr, Dalton S. Hardisty, Allison Jacobel, Dharma Reyes Macaya, Nicolaas Glock, Sha Ni, Julio Sepúlveda, Abby Ren, Alexandra Auderset, Anya V. Hess, Katrin J. Meissner, Jorge Cardich, Robert Anderson, Christine Barras, Chandranath Basak, Harold J. Bradbury, Inda Brinkmann, Alexis Castillo, Madelyn Cook, Kassandra Costa, Constance Choquel, Paula Diz, Jonas Donnenfield, Felix J. Elling, Zeynep Erdem, Helena L. Filipsson, Sebastián Garrido, Julia Gottschalk, Anjaly Govindankutty Menon, Jeroen Groeneveld, Christian Hallmann, Ingrid Hendy, Rick Hennekam, Wanyi Lu, Jean Lynch-Stieglitz, Lélia Matos, Alfredo Martínez-García, Giulia Molina, Práxedes Muñoz, Simone Moretti, Jennifer Morford, Sophie Nuber, Svetlana Radionovskaya, Morgan Reed Raven, Christopher J. Somes, Anja S. Studer, Kazuyo Tachikawa, Raúl Tapia, Martin Tetard, Tyler Vollmer, Xingchen Wang, Shuzhuang Wu, Yan Zhang, Xin-Yuan Zheng, and Yuxin Zhou
Biogeosciences, 22, 863–957, https://doi.org/10.5194/bg-22-863-2025, https://doi.org/10.5194/bg-22-863-2025, 2025
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Paleo-oxygen proxies can extend current records, constrain pre-anthropogenic baselines, provide datasets necessary to test climate models under different boundary conditions, and ultimately understand how ocean oxygenation responds on longer timescales. Here we summarize current proxies used for the reconstruction of Cenozoic seawater oxygen levels. This includes an overview of the proxy's history, how it works, resources required, limitations, and future recommendations.
Judit Torner, Isabel Cacho, Heather Stoll, Ana Moreno, Joan O. Grimalt, Francisco J. Sierro, Joan J. Fornós, Hai Cheng, and R. Lawrence Edwards
Clim. Past, 21, 465–487, https://doi.org/10.5194/cp-21-465-2025, https://doi.org/10.5194/cp-21-465-2025, 2025
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We offer a clearer view of the timing of three relevant past glacial terminations. By analyzing the climatic signal recorded in stalagmite and linking it with marine records, we revealed differences in the intensity and duration of the ice melting associated with these three key deglaciations. This study shows that some deglaciations began earlier than previously thought; this improves our understanding of natural climate processes, helping us to contextualize current climate change.
Konstantina Agiadi, Niklas Hohmann, Elsa Gliozzi, Danae Thivaiou, Francesca R. Bosellini, Marco Taviani, Giovanni Bianucci, Alberto Collareta, Laurent Londeix, Costanza Faranda, Francesca Bulian, Efterpi Koskeridou, Francesca Lozar, Alan Maria Mancini, Stefano Dominici, Pierre Moissette, Ildefonso Bajo Campos, Enrico Borghi, George Iliopoulos, Assimina Antonarakou, George Kontakiotis, Evangelia Besiou, Stergios D. Zarkogiannis, Mathias Harzhauser, Francisco Javier Sierro, Angelo Camerlenghi, and Daniel García-Castellanos
Earth Syst. Sci. Data, 16, 4767–4775, https://doi.org/10.5194/essd-16-4767-2024, https://doi.org/10.5194/essd-16-4767-2024, 2024
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We present a dataset of 23032 fossil occurrences of marine organisms from the Late Miocene to the Early Pliocene (~11 to 3.6 million years ago) from the Mediterranean Sea. This dataset will allow us, for the first time, to quantify the biodiversity impact of the Messinian salinity crisis, a major geological event that possibly changed global and regional climate and biota.
Thibauld M. Béjard, Andrés S. Rigual-Hernández, Javier P. Tarruella, José-Abel Flores, Anna Sanchez-Vidal, Irene Llamas-Cano, and Francisco J. Sierro
Biogeosciences, 21, 4051–4076, https://doi.org/10.5194/bg-21-4051-2024, https://doi.org/10.5194/bg-21-4051-2024, 2024
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The Mediterranean Sea is regarded as a climate change hotspot. Documenting the population of planktonic foraminifera is crucial. In the Sicily Channel, fluxes are higher during winter and positively linked with chlorophyll a concentration and cool temperatures. A comparison with other Mediterranean sites shows the transitional aspect of the studied zone. Finally, modern populations significantly differ from those in the sediment, highlighting a possible effect of environmental change.
Mohamed Ayache, Jean-Claude Dutay, Anne Mouchet, Kazuyo Tachikawa, Camille Risi, and Gilles Ramstein
Geosci. Model Dev., 17, 6627–6655, https://doi.org/10.5194/gmd-17-6627-2024, https://doi.org/10.5194/gmd-17-6627-2024, 2024
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Water isotopes (δ18O, δD) are one of the most widely used proxies in ocean climate research. Previous studies using water isotope observations and modelling have highlighted the importance of understanding spatial and temporal isotopic variability for a quantitative interpretation of these tracers. Here we present the first results of a high-resolution regional dynamical model (at 1/12° horizontal resolution) developed for the Mediterranean Sea, one of the hotspots of ongoing climate change.
Carlo Mologni, Marie Revel, Eric Chaumillon, Emmanuel Malet, Thibault Coulombier, Pierre Sabatier, Pierre Brigode, Gwenael Hervé, Anne-Lise Develle, Laure Schenini, Medhi Messous, Gourguen Davtian, Alain Carré, Delphine Bosch, Natacha Volto, Clément Ménard, Lamya Khalidi, and Fabien Arnaud
Clim. Past, 20, 1837–1860, https://doi.org/10.5194/cp-20-1837-2024, https://doi.org/10.5194/cp-20-1837-2024, 2024
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The reactivity of local to regional hydrosystems to global changes remains understated in East African climate models. By reconstructing a chronicle of seasonal floods and droughts from a lacustrine sedimentary core, this paper highlights the impact of El Niño anomalies in the Awash River valley (Ethiopia). Studying regional hydrosystem feedbacks to global atmospheric anomalies is essential for better comprehending and mitigating the effects of global warming in extreme environments.
Nicole Burdanowitz, Gerhard Schmiedl, Birgit Gaye, Philipp M. Munz, and Hartmut Schulz
Biogeosciences, 21, 1477–1499, https://doi.org/10.5194/bg-21-1477-2024, https://doi.org/10.5194/bg-21-1477-2024, 2024
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We analyse benthic foraminifera, nitrogen isotopes and lipids in a sediment core from the Gulf of Oman to investigate how the oxygen minimum zone (OMZ) and bottom water (BW) oxygenation have reacted to climatic changes since 43 ka. The OMZ and BW deoxygenation was strong during the Holocene, but the OMZ was well ventilated during the LGM period. We found an unstable mode of oscillating oxygenation states, from moderately oxygenated in cold stadials to deoxygenated in warm interstadials in MIS 3.
Werner Ehrmann, Paul A. Wilson, Helge W. Arz, Hartmut Schulz, and Gerhard Schmiedl
Clim. Past, 20, 37–52, https://doi.org/10.5194/cp-20-37-2024, https://doi.org/10.5194/cp-20-37-2024, 2024
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Climatic and associated hydrological changes controlled the aeolian versus fluvial transport processes and the composition of the sediments in the central Red Sea through the last ca. 200 kyr. We identify source areas of the mineral dust and pulses of fluvial discharge based on high-resolution grain size, clay mineral, and geochemical data, together with Nd and Sr isotope data. We provide a detailed reconstruction of changes in aridity/humidity.
Elwyn de la Vega, Thomas B. Chalk, Mathis P. Hain, Megan R. Wilding, Daniel Casey, Robin Gledhill, Chongguang Luo, Paul A. Wilson, and Gavin L. Foster
Clim. Past, 19, 2493–2510, https://doi.org/10.5194/cp-19-2493-2023, https://doi.org/10.5194/cp-19-2493-2023, 2023
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We evaluate how faithfully the boron isotope composition of foraminifera records atmospheric CO2 by comparing it to the high-fidelity CO2 record from the Antarctic ice cores. We evaluate potential factors and find that partial dissolution of foraminifera shells, assumptions of seawater chemistry, and the biology of foraminifera all have a negligible effect on reconstructed CO2. This gives confidence in the use of boron isotopes beyond the interval when ice core CO2 is available.
Guillaume Soulet, Philippe Maestrati, Serge Gofas, Germain Bayon, Fabien Dewilde, Maylis Labonne, Bernard Dennielou, Franck Ferraton, and Giuseppe Siani
Geochronology, 5, 345–359, https://doi.org/10.5194/gchron-5-345-2023, https://doi.org/10.5194/gchron-5-345-2023, 2023
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The marine reservoir age (MRA) is the difference between the 14C age of the ocean and that of the atmosphere at a given time. In geochronology, knowing the local MRA is important to derive accurate calibrated ages for 14C-dated marine material. However, MRA values for coastal West Africa are scarce. From the 14C dating of known-age bivalves from museum collections, we calculated MRA values and populated the MRA dataset for coastal West Africa over a latitudinal transect from 33°N to 15°S.
Thibauld M. Béjard, Andrés S. Rigual-Hernández, José A. Flores, Javier P. Tarruella, Xavier Durrieu de Madron, Isabel Cacho, Neghar Haghipour, Aidan Hunter, and Francisco J. Sierro
Biogeosciences, 20, 1505–1528, https://doi.org/10.5194/bg-20-1505-2023, https://doi.org/10.5194/bg-20-1505-2023, 2023
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The Mediterranean Sea is undergoing a rapid and unprecedented environmental change. Planktic foraminifera calcification is affected on different timescales. On seasonal and interannual scales, calcification trends differ according to the species and are linked mainly to sea surface temperatures and carbonate system parameters, while comparison with pre/post-industrial assemblages shows that all three species have reduced their calcification between 10 % to 35 % according to the species.
Suzanne Robinson, Ruza F. Ivanovic, Lauren J. Gregoire, Julia Tindall, Tina van de Flierdt, Yves Plancherel, Frerk Pöppelmeier, Kazuyo Tachikawa, and Paul J. Valdes
Geosci. Model Dev., 16, 1231–1264, https://doi.org/10.5194/gmd-16-1231-2023, https://doi.org/10.5194/gmd-16-1231-2023, 2023
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We present the implementation of neodymium (Nd) isotopes into the ocean model of FAMOUS (Nd v1.0). Nd fluxes from seafloor sediment and incorporation of Nd onto sinking particles represent the major global sources and sinks, respectively. However, model–data mismatch in the North Pacific and northern North Atlantic suggest that certain reactive components of the sediment interact the most with seawater. Our results are important for interpreting Nd isotopes in terms of ocean circulation.
Mohamed Ayache, Jean-Claude Dutay, Kazuyo Tachikawa, Thomas Arsouze, and Catherine Jeandel
Biogeosciences, 20, 205–227, https://doi.org/10.5194/bg-20-205-2023, https://doi.org/10.5194/bg-20-205-2023, 2023
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The neodymium (Nd) is one of the most useful tracers to fingerprint water mass provenance. However, the use of Nd is hampered by the lack of adequate quantification of the external sources. Here, we present the first simulation of dissolved Nd concentration and Nd isotopic composition in the Mediterranean Sea using a high-resolution model. We aim to better understand how the various external sources affect the Nd cycle and particularly assess how it is impacted by atmospheric inputs.
Suzanne Robinson, Ruza Ivanovic, Lauren Gregoire, Lachlan Astfalck, Tina van de Flierdt, Yves Plancherel, Frerk Pöppelmeier, and Kazuyo Tachikawa
EGUsphere, https://doi.org/10.5194/egusphere-2022-937, https://doi.org/10.5194/egusphere-2022-937, 2022
Preprint archived
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The neodymium (Nd) isotope (εNd) scheme in the ocean model of FAMOUS is used to explore a benthic Nd flux to seawater. Our results demonstrate that sluggish modern Pacific waters are sensitive to benthic flux alterations, whereas the well-ventilated North Atlantic displays a much weaker response. In closing, there are distinct regional differences in how seawater acquires its εNd signal, in part relating to the complex interactions of Nd addition and water advection.
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.
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Short summary
Direct observations indicate a decline in ocean oxygen concentration. The complexity of surface oxygen variability is linked to physical and biochemical parameters. To investigate past oxygen variability, foraminiferal I/Ca proxy must be calibrated. Here, we determine the drivers of the proxy using a database of modern samples. From our results, oxygen is the principal driver of the I/Ca proxy. We highlight its complex behaviour, while reinforcing its use for palaeoceanographic reconstructions.
Direct observations indicate a decline in ocean oxygen concentration. The complexity of surface...
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