Articles | Volume 21, issue 6
https://doi.org/10.5194/cp-21-973-2025
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the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
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https://doi.org/10.5194/cp-21-973-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
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03 Jun 2025
Research article | Highlight paper |
| 03 Jun 2025
| 03 Jun 2025
Mean ocean temperature change and decomposition of the benthic δ18O record over the past 4.5 million years
College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
School of Geography and Environmental Sciences, University of Ulster, Coleraine, BT52 1SA, Northern Ireland, UK
Invited contribution by Peter U. Clark, recipient of the EGU Milutin Milanković Medal 2024.
Jeremy D. Shakun
Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467, USA
Yair Rosenthal
Department of Marine and Coastal Science, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA
Chenyu Zhu
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Patrick J. Bartlein
Department of Geography, University of Oregon, Eugene, OR 97403-1251, USA
Jonathan M. Gregory
National Center for Atmospheric Science, University of Reading, Reading, UK
Met Office Hadley Centre, Exeter, UK
Peter Köhler
Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
Zhengyu Liu
Department of Geography, The Ohio State University, Columbus, OH 43210, USA
Daniel P. Schrag
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
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Peyton M. Cavnar, Paul R. Bierman, Jeremy D. Shakun, Lee B. Corbett, Danielle LeBlanc, Gillian L. Galford, Pierre-Olivier Couette, Jean-Francois Ghienne, Patrick Lajeunesse, Jérôme van der Woerd, and Marc Caffee
Geochronology, 8, 119–141, https://doi.org/10.5194/gchron-8-119-2026, https://doi.org/10.5194/gchron-8-119-2026, 2026
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To investigate the Laurentide Ice Sheet’s erosivity before and during the Last Glacial Maximum, we sampled sand deposited by ice in eastern Canada before final deglaciation. We also sampled modern river sand. The 26Al and 10Be measured in glacial deposited sediments suggests that ice remained during some Pleistocene warm periods and was an inefficient eroder. Similar concentrations of 26Al and 10Be in modern sand suggests that most modern river sediment is sourced from glacial deposits.
Paulo Ceppi, Alejandro Bodas-Salcedo, Mark D. Zelinka, Timothy Andrews, Florent Brient, Robin Chadwick, Jonathan M. Gregory, Yen-Ting Hwang, Sarah M. Kang, Jennifer E. Kay, Thorsten Mauritsen, Tomoo Ogura, George Tselioudis, Masahiro Watanabe, Mark J. Webb, and Allison A. Wing
EGUsphere, https://doi.org/10.5194/egusphere-2026-398, https://doi.org/10.5194/egusphere-2026-398, 2026
This preprint is open for discussion and under review for Geoscientific Model Development (GMD).
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Clouds constitute a key uncertainty for climate change projections. The Cloud Feedback Model Intercomparison Project (CFMIP) aims to address this challenge by evaluating and understanding clouds and their impacts on atmospheric circulation, precipitation, and climate sensitivity. The present paper describes the CFMIP experiment protocol for the Coupled Model Intercomparison Project phase 7 (CMIP7), and discusses the accompanying science questions and opportunities for progress.
Chengwei Ji, Qin Wen, Zhengyu Liu, Jian Liu, Deliang Chen, Liang Ning, Mi Yan, and Qiuzhen Yin
EGUsphere, https://doi.org/10.5194/egusphere-2025-5029, https://doi.org/10.5194/egusphere-2025-5029, 2025
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Geologist commonly use speleothem δ18Oc records to reconstruct past North African monsoon variability based on “amount effect” relationship between δ18Oc and monsoon rainfall. However, the interpretation of these records has been challenged in recent years. Here, we use isotope-enabled climate model to simulate climate change during the past 150,000 years. We find that changes in δ18Op across North African region are caused by multiple atmospheric processes, rather than by “amount effect”.
Peter Köhler, Laurie Menviel, Frerk Pöppelmeier, Tim J. Heaton, Edouard Bard, and Luke C. Skinner
EGUsphere, https://doi.org/10.5194/egusphere-2025-5136, https://doi.org/10.5194/egusphere-2025-5136, 2025
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Radiocarbon (14C) is decaying over time, which is used to determine the age of carbon-containing objects. Calibration curves are necessary to come from measured 14C values to calendar ages. We use different models in order to improve future calibration curves, especially around times of abrupt changes in the Atlantic meridional overturning circulation. We find that uncertainties during those times are underrepresented in present calibrations, especially in the Atlantic.
Tal Y. Shutkin, Bryan G. Mark, Nathan D. Stansell, Rolando Cruz Encarnación, Henry H. Brecher, Zhengyu Liu, Bidhyananda Yadav, and Forrest S. Schoessow
The Cryosphere, 19, 4835–4853, https://doi.org/10.5194/tc-19-4835-2025, https://doi.org/10.5194/tc-19-4835-2025, 2025
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Queshque Glacier of Peru's tropical Andes has retreated rapidly since the mid-20th century. Using a glacier model, we show that this has primarily been driven by steady warming despite the counteracting effect of recent snowfall amounts. Independently from climatic trends, we find that the formation of a new lake at the glacier's base has further accelerated ice loss. This research demonstrates the utility of empirical glacier models for interpreting past and future changes in the tropics.
Takashi Obase, Laurie Menviel, Ayako Abe-Ouchi, Tristan Vadsaria, Ruza Ivanovic, Brooke Snoll, Sam Sherriff-Tadano, Paul J. Valdes, Lauren Gregoire, Marie-Luise Kapsch, Uwe Mikolajewicz, Nathaelle Bouttes, Didier Roche, Fanny Lhardy, Chengfei He, Bette Otto-Bliesner, Zhengyu Liu, and Wing-Le Chan
Clim. Past, 21, 1443–1463, https://doi.org/10.5194/cp-21-1443-2025, https://doi.org/10.5194/cp-21-1443-2025, 2025
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This study analyses transient simulations of the last deglaciation performed by six climate models to understand the processes driving high-southern-latitude temperature changes. We find that atmospheric CO2 and AMOC (Atlantic Meridional Overturning Circulation) changes are the primary drivers of the warming and cooling during the middle stage of the deglaciation. The analysis highlights the model's sensitivity of CO2 and AMOC to meltwater and the meltwater history of temperature changes at high southern latitudes.
Peter Köhler
Clim. Past, 21, 1043–1060, https://doi.org/10.5194/cp-21-1043-2025, https://doi.org/10.5194/cp-21-1043-2025, 2025
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Using a carbon cycle model, I show that the 405 kyr periodicity found in marine δ13C during the last 5 million years and the offset in atmospheric δ13CO2 between the Last Glacial Maximum and the Penultimate Glacial Maximum are probably related to each other. They can be explained by variations in the δ13C signature of weathered carbonate rock or of volcanically degassed CO2, which vary mainly with obliquity (41 kyr), suggesting that Northern Hemispheric land ice sheets are their ultimate drivers.
Ying Ye, Guy Munhoven, Peter Köhler, Martin Butzin, Judith Hauck, Özgür Gürses, and Christoph Völker
Geosci. Model Dev., 18, 977–1000, https://doi.org/10.5194/gmd-18-977-2025, https://doi.org/10.5194/gmd-18-977-2025, 2025
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Many biogeochemistry models assume all material reaching the seafloor is remineralized and returned to solution, which is sufficient for studies on short-term climate change. Under long-term climate change, the carbon storage in sediments slows down carbon cycling and influences feedbacks in the atmosphere–ocean–sediment system. This paper describes the coupling of a sediment model to an ocean biogeochemistry model and presents results under the pre-industrial climate and under CO2 perturbation.
Sam Sherriff-Tadano, Ruza Ivanovic, Lauren Gregoire, Charlotte Lang, Niall Gandy, Jonathan Gregory, Tamsin L. Edwards, Oliver Pollard, and Robin S. Smith
Clim. Past, 20, 1489–1512, https://doi.org/10.5194/cp-20-1489-2024, https://doi.org/10.5194/cp-20-1489-2024, 2024
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Ensemble simulations of the climate and ice sheets of the Last Glacial Maximum (LGM) are performed with a new coupled climate–ice sheet model. Results show a strong sensitivity of the North American ice sheet to the albedo scheme, while the Greenland ice sheet appeared more sensitive to basal sliding schemes. Our result implies a potential connection between the North American ice sheet at the LGM and the future Greenland ice sheet through the albedo scheme.
Lingwei Li, Zhengyu Liu, Jinbo Du, Lingfeng Wan, and Jiuyou Lu
Clim. Past, 20, 1161–1175, https://doi.org/10.5194/cp-20-1161-2024, https://doi.org/10.5194/cp-20-1161-2024, 2024
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Radiocarbon proxies suggest that the deep waters are poorly ventilated during the Last Glacial Maximum (LGM). Here we use two transient simulations with tracers of radiocarbon and ideal age to show that the deep-ocean ventilation age is not much older at the LGM compared to the present day because of the strong glacial Antarctic Bottom Water transport. In contrast, the ventilation age is older during deglaciation mainly due to weakening of Antarctic Bottom Water transport.
Peter Köhler and Stefan Mulitza
Clim. Past, 20, 991–1015, https://doi.org/10.5194/cp-20-991-2024, https://doi.org/10.5194/cp-20-991-2024, 2024
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We constructed 160 kyr long mono-specific stacks of δ13C and of δ18O from the wider tropics from the planktic foraminifera G. ruber and/or T. sacculifer and compared them with carbon cycle simulations using the BICYCLE-SE model. In our stacks and our model-based interpretation, we cannot detect a species-specific isotopic fractionation during hard-shell formation as a function of carbonate chemistry in the surrounding seawater, something which is called a carbonate ion effect.
Martin Butzin, Ying Ye, Christoph Völker, Özgür Gürses, Judith Hauck, and Peter Köhler
Geosci. Model Dev., 17, 1709–1727, https://doi.org/10.5194/gmd-17-1709-2024, https://doi.org/10.5194/gmd-17-1709-2024, 2024
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In this paper we describe the implementation of the carbon isotopes 13C and 14C into the marine biogeochemistry model FESOM2.1-REcoM3 and present results of long-term test simulations. Our model results are largely consistent with marine carbon isotope reconstructions for the pre-anthropogenic period, but also exhibit some discrepancies.
Robert E. Kopp, Gregory G. Garner, Tim H. J. Hermans, Shantenu Jha, Praveen Kumar, Alexander Reedy, Aimée B. A. Slangen, Matteo Turilli, Tamsin L. Edwards, Jonathan M. Gregory, George Koubbe, Anders Levermann, Andre Merzky, Sophie Nowicki, Matthew D. Palmer, and Chris Smith
Geosci. Model Dev., 16, 7461–7489, https://doi.org/10.5194/gmd-16-7461-2023, https://doi.org/10.5194/gmd-16-7461-2023, 2023
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Future sea-level rise projections exhibit multiple forms of uncertainty, all of which must be considered by scientific assessments intended to inform decision-making. The Framework for Assessing Changes To Sea-level (FACTS) is a new software package intended to support assessments of global mean, regional, and extreme sea-level rise. An early version of FACTS supported the development of the IPCC Sixth Assessment Report sea-level projections.
Andrew G. Jones, Shaun A. Marcott, Andrew L. Gorin, Tori M. Kennedy, Jeremy D. Shakun, Brent M. Goehring, Brian Menounos, Douglas H. Clark, Matias Romero, and Marc W. Caffee
The Cryosphere, 17, 5459–5475, https://doi.org/10.5194/tc-17-5459-2023, https://doi.org/10.5194/tc-17-5459-2023, 2023
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Mountain glaciers today are fractions of their sizes 140 years ago, but how do these sizes compare to the past 11,000 years? We find that four glaciers in the United States and Canada have reversed a long-term trend of growth and retreated to positions last occupied thousands of years ago. Notably, each glacier occupies a unique position relative to its long-term history. We hypothesize that unequal modern retreat has caused the glaciers to be out of sync relative to their Holocene histories.
Hélène Seroussi, Vincent Verjans, Sophie Nowicki, Antony J. Payne, Heiko Goelzer, William H. Lipscomb, Ayako Abe-Ouchi, Cécile Agosta, Torsten Albrecht, Xylar Asay-Davis, Alice Barthel, Reinhard Calov, Richard Cullather, Christophe Dumas, Benjamin K. Galton-Fenzi, Rupert Gladstone, Nicholas R. Golledge, Jonathan M. Gregory, Ralf Greve, Tore Hattermann, Matthew J. Hoffman, Angelika Humbert, Philippe Huybrechts, Nicolas C. Jourdain, Thomas Kleiner, Eric Larour, Gunter R. Leguy, Daniel P. Lowry, Chistopher M. Little, Mathieu Morlighem, Frank Pattyn, Tyler Pelle, Stephen F. Price, Aurélien Quiquet, Ronja Reese, Nicole-Jeanne Schlegel, Andrew Shepherd, Erika Simon, Robin S. Smith, Fiammetta Straneo, Sainan Sun, Luke D. Trusel, Jonas Van Breedam, Peter Van Katwyk, Roderik S. W. van de Wal, Ricarda Winkelmann, Chen Zhao, Tong Zhang, and Thomas Zwinger
The Cryosphere, 17, 5197–5217, https://doi.org/10.5194/tc-17-5197-2023, https://doi.org/10.5194/tc-17-5197-2023, 2023
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Mass loss from Antarctica is a key contributor to sea level rise over the 21st century, and the associated uncertainty dominates sea level projections. We highlight here the Antarctic glaciers showing the largest changes and quantify the main sources of uncertainty in their future evolution using an ensemble of ice flow models. We show that on top of Pine Island and Thwaites glaciers, Totten and Moscow University glaciers show rapid changes and a strong sensitivity to warmer ocean conditions.
Luke Skinner, Francois Primeau, Aurich Jeltsch-Thömmes, Fortunat Joos, Peter Köhler, and Edouard Bard
Clim. Past, 19, 2177–2202, https://doi.org/10.5194/cp-19-2177-2023, https://doi.org/10.5194/cp-19-2177-2023, 2023
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Radiocarbon is best known as a dating tool, but it also allows us to track CO2 exchange between the ocean and atmosphere. Using decades of data and novel mapping methods, we have charted the ocean’s average radiocarbon ″age” since the last Ice Age. Combined with climate model simulations, these data quantify the ocean’s role in atmospheric CO2 rise since the last Ice Age while also revealing that Earth likely received far more cosmic radiation during the last Ice Age than hitherto believed.
Esmeralda Cruz-Silva, Sandy P. Harrison, I. Colin Prentice, Elena Marinova, Patrick J. Bartlein, Hans Renssen, and Yurui Zhang
Clim. Past, 19, 2093–2108, https://doi.org/10.5194/cp-19-2093-2023, https://doi.org/10.5194/cp-19-2093-2023, 2023
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We examined 71 pollen records (12.3 ka to present) in the eastern Mediterranean, reconstructing climate changes. Over 9000 years, winters gradually warmed due to orbital factors. Summer temperatures peaked at 4.5–5 ka, likely declining because of ice sheets. Moisture increased post-11 kyr, remaining high from 10–6 kyr before a slow decrease. Climate models face challenges in replicating moisture transport.
Claudia Hinrichs, Peter Köhler, Christoph Völker, and Judith Hauck
Biogeosciences, 20, 3717–3735, https://doi.org/10.5194/bg-20-3717-2023, https://doi.org/10.5194/bg-20-3717-2023, 2023
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This study evaluated the alkalinity distribution in 14 climate models and found that most models underestimate alkalinity at the surface and overestimate it in the deeper ocean. It highlights the need for better understanding and quantification of processes driving alkalinity distribution and calcium carbonate dissolution and the importance of accounting for biases in model results when evaluating potential ocean alkalinity enhancement experiments.
Aaron M. Barth, Elizabeth G. Ceperley, Claire Vavrus, Shaun A. Marcott, Jeremy D. Shakun, and Marc W. Caffee
Geochronology, 4, 731–743, https://doi.org/10.5194/gchron-4-731-2022, https://doi.org/10.5194/gchron-4-731-2022, 2022
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Deposits left behind by past glacial activity provide insight into the previous size and behavior of glaciers and act as another line of evidence for past climate. Here we present new age control for glacial deposits in the mountains of Montana and Wyoming, United States. While some deposits indicate glacial activity within the last 2000 years, others are shown to be older than previously thought, thus redefining the extent of regional Holocene glaciation.
Antony Siahaan, Robin S. Smith, Paul R. Holland, Adrian Jenkins, Jonathan M. Gregory, Victoria Lee, Pierre Mathiot, Antony J. Payne, Jeff K. Ridley, and Colin G. Jones
The Cryosphere, 16, 4053–4086, https://doi.org/10.5194/tc-16-4053-2022, https://doi.org/10.5194/tc-16-4053-2022, 2022
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The UK Earth System Model is the first to fully include interactions of the atmosphere and ocean with the Antarctic Ice Sheet. Under the low-greenhouse-gas SSP1–1.9 (Shared Socioeconomic Pathway) scenario, the ice sheet remains stable over the 21st century. Under the strong-greenhouse-gas SSP5–8.5 scenario, the model predicts strong increases in melting of large ice shelves and snow accumulation on the surface. The dominance of accumulation leads to a sea level fall at the end of the century.
Robin S. Smith, Steve George, and Jonathan M. Gregory
Geosci. Model Dev., 14, 5769–5787, https://doi.org/10.5194/gmd-14-5769-2021, https://doi.org/10.5194/gmd-14-5769-2021, 2021
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Many of the complex computer models used to study the physics of the natural world treat ice sheets as fixed and unchanging, capable of only simple interactions with the rest of the climate. This is partly because it is technically very difficult to usefully do anything more realistic. We have adapted a climate model so it can be joined together with a dynamical model of the Greenland ice sheet. This gives us a powerful tool to help us better understand how ice sheets and the climate interact.
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This Milankovic Medalist paper represents a tour de force, addressing a complex yet crucial question: the evolution of global climate over the past 4.5 million years. This paper makes a significant contribution to the geoscience community by providing a self-consistent decomposition of global mean benthic δ18O into its temperature and seawater (ice volume) components.
This approach is consistent with independent estimates of global mean sea surface temperature (GMSST) and sea level constraints.The analysis incorporates numerous high-resolution records spanning this period and highlights two distinct climatic regimes:
• Before 1.5 million years ago, a warm period characterized by smaller-amplitude ice sheet and sea level cycles, primarily driven by obliquity timescales.
• Following the Mid-Pleistocene Transition (MPT), i.e. after 1 million years, a well-documented increase in the amplitude of glacial cycles became evident.
The central finding of the study is that, during the MPT, there was a shift in ocean heat storage efficiency (HSE). Prior to this transition, HSE remained low and constant, whereas after the MPT, it doubled and stabilized at a higher value. This finding is supported by the observation of subtle differential changes in global mean SST and mean ocean temperature (MOT), which appear to be time-dependent. These observations suggest a potential fundamental shift in oceanic heat storage dynamics.
This Milankovic Medalist paper represents a tour de force, addressing a complex yet crucial...
Short summary
We reconstruct changes in mean ocean temperature (ΔMOT) over the last 4.5 Myr. We find that the ratio of ΔMOT to changes in global mean sea surface temperature was around 0.5 before the Middle Pleistocene transition but was 1 thereafter. We subtract our ΔMOT reconstruction from the global δ18O record to derive the δ18O of seawater. Finally, we develop a theoretical understanding of why the ratio of ΔMOT / ΔGMSST changed over the Plio-Pleistocene.
We reconstruct changes in mean ocean temperature (ΔMOT) over the last 4.5 Myr. We find that the...
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