Ocean Circulation and Carbon Cycle Dynamics During Glacial Periods

During glacial epochs, changes in large‐scale ocean circulation exerted a profound control on atmospheric carbon dioxide levels and global climate. Cooler temperatures, expanded sea ice and altered wind patterns modified the strength and structure of key currents—most notably the Atlantic Meridional Overturning Circulation and the Antarctic Circumpolar Current. These shifts regulated the upwelling of nutrient- and carbon-rich deep waters, influencing the efficiency of the biological carbon pump and the residence time of dissolved inorganic carbon. Enhanced stratification and reduced air–sea gas exchange at low temperatures promoted the sequestration of respired carbon in the deep ocean, contributing to significant glacial–interglacial CO₂ drawdown. Recent reconstructions reveal that subtropical gyres were deeper and stronger, that iron-cycle feedbacks could reverse expected circulation–CO₂ relationships, and that circumpolar current migrations drove pulses of Southern Ocean degassing. Together, these findings underscore the tight coupling between physical circulation, biogeochemical processes and external forcings such as orbital insolation and freshwater inputs. A comprehensive understanding of these mechanisms is essential for anticipating how modern ocean dynamics may respond to ongoing anthropogenic perturbations.

Research from Nature Portfolio

Recent work demonstrates that during the Last Glacial Maximum the North Atlantic subtropical gyre extended roughly 1 km deeper than today and strengthened in response to increased wind stress curl and surface buoyancy loss. This deepened gyre enhanced water-mass conversion and bolstered northward heat transport, with implications for nutrient and carbon redistribution across the North Atlantic.

Modelling studies incorporating dynamic organic ligand parameterisations show that feedbacks in the ocean iron cycle can invert the conventional relationship between overturning circulation and atmospheric CO₂. A weakened overturning reduces ligand production, intensifies iron limitation, curtails nutrient consumption and, counterintuitively, promotes net carbon outgassing under low-upwelling conditions.

Quantitative reconstructions of the Antarctic Circumpolar Current over the last glacial–interglacial cycle reveal an equatorward position during glacial maxima and a ~6° poleward migration at terminations. These latitudinal shifts controlled wind-driven upwelling and CO₂ degassing in the Southern Ocean, highlighting the sensitivity of atmospheric carbon to circumpolar dynamics.

Ocean Circulation and Carbon Cycle Dynamics During Glacial Periods publication trend

The graph below shows the total number of articles in ocean circulation and carbon cycle dynamics during glacial periods across all publications each year (not limited to Nature Index journals).

Technical terms

Meridional Overturning Circulation (MOC): Global system of surface and deep currents that transports heat, nutrients and carbon between low and high latitudes.

Biological carbon pump: Process by which marine organisms fix CO₂ in surface waters and export organic carbon to the ocean interior.

Upwelling: Rise of deep, nutrient-and carbon-rich waters to the ocean surface driven by winds or density gradients.

Air–sea gas exchange: Transfer of gases, including CO₂, between the atmosphere and the ocean surface.

Ocean ventilation: Renewal of surface waters via mixing and circulation, affecting oxygenation and carbon storage.

Antarctic Circumpolar Current (ACC): Strong, circumpolar flow around Antarctica that regulates global ocean connectivity and modulates upwelling.

References

1. Deeper and stronger North Atlantic Gyre during the Last Glacial Maximum. Nature (2024).
2. Ocean iron cycle feedbacks decouple atmospheric CO2 from meridional overturning circulation changes. Nature Communications (2024).
3. The southward migration of the Antarctic Circumpolar Current enhanced oceanic degassing of carbon dioxide during the last two deglaciations. Communications Earth & Environment (2024).
4. Southern Ocean drives multidecadal atmospheric CO2 rise during Heinrich Stadials. Proceedings of the National Academy of Sciences of the United States of America (2024).
5. Air-sea disequilibrium enhances ocean carbon storage during glacial periods. Science Advances (2019).
6. Simulation of climate, ice sheets and CO2 evolution during the last four glacial cycles with an Earth system model of intermediate complexity. Climate of the Past (2017).