Studying the ocean carbon cycle under past climate conditions helps us understand the feedbacks and sensitivities at play. Several processes affect ocean carbon uptake during cold stadial periods, including temperature-induced changes in CO₂ solubility, isolation of the deep ocean, reduced air-sea gas exchange due to sea ice expansion, and iron-induced changes in marine productivity. The gradual decrease in atmospheric CO₂ as Earth cools into a glacial maximum during the late Quaternary suggests a sequencing of mechanisms of carbon uptake. However, most data compilation and modeling studies have focused on the Last Glacial Maximum (LGM; 28 – 18 ka). At its peak, MIS 4 (69 – 62 ka), was almost as extreme as the LGM, with 87% of full glacial-interglacial amplitude for CO₂, 84% for Antarctic temperature, 92% for sea-level, and 89% for global SST. Here we analyse proxy compilations to compare ocean carbon uptake mechanisms between Marine Isotope Stages 2 and 4.

Zanna Chase is Associate Professor of Chemical Oceanography at the University of Tasmania, Australia. She works within the Oceans and Cryosphere Centre at the Institute for Marine and Antarctic Studies. Her research focuses on the interaction between chemical cycles and biological activity in the oceans, and how these are affected by climate.