Here we use high-precision carbon isotope data (δ13C-CO2) to show atmospheric CO2during Marine Isotope Stage 4 (MIS 4, ~70.5-59 ka) was controlled by a succession of millennial-scale processes. Enriched δ13C-CO2during peak glaciation suggests increased ocean carbon storage. Variations in δ13C-CO2in early MIS 4 suggest multiple processes were active during CO2drawdown, potentially including decreased land carbon and decreased Southern Ocean air-sea gas exchange superposed on increased ocean carbon storage. CO2remained low during MIS 4 while δ13C-CO2fluctuations suggest changes in Southern Ocean and North Atlantic air-sea gas exchange. A 7 ppm increase in CO2at the onset of Dansgaard-Oeschger event 19 (72.1 ka) and 27 ppm increase in CO2during late MIS 4 (Heinrich Stadial 6, ~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.
This content will become publicly available on December 21, 2022
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