Multiple carbon cycle mechanisms associated with the glaciation of Marine Isotope Stage 4

Here we use high-precision carbon isotope data (delta C-13-CO2) to show atmospheric CO2 during Marine Isotope Stage 4 (MIS 4, similar to 70.5-59 ka) was controlled by a succession of millennial-scale processes. Enriched delta C-13-CO2 during peak glaciation suggests increased ocean carbon storage. Variations in delta C-13-CO2 in early MIS 4 suggest multiple processes were active during CO2 drawdown, potentially including decreased land carbon and decreased Southern Ocean air-sea gas exchange superposed on increased ocean carbon storage. CO2 remained low during MIS 4 while delta C-13-CO2 fluctuations suggest changes in Southern Ocean and North Atlantic air-sea gas exchange. A 7 ppm increase in CO2 at the onset of Dansgaard-Oeschger event 19 (72.1 ka) and 27 ppm increase in CO2 during late MIS 4 (Heinrich Stadial 6, similar to 63.5-60 ka) involved additions of isotopically light carbon to the atmosphere. The terrestrial biosphere and Southern Ocean air-sea gas exchange are possible sources, with the latter event also involving decreased ocean carbon storage.

Automated summary

Using high-precision carbon isotope data, this study reveals that atmospheric CO2 during Marine Isotope Stage 4 was influenced by millennial-scale processes. Changes in ocean carbon storage, land carbon, and air-sea gas exchange in the Southern Ocean were responsible for variations in CO2 levels. Additionally, isotopically light carbon injections from the terrestrial biosphere and Southern Ocean contributed to CO2 increases during specific events.