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

Here we use high-precision carbon isotope data (δ(13)C-CO(2)) to show atmospheric CO(2) during Marine Isotope Stage 4 (MIS 4, ~70.5-59 ka) was controlled by a succession of millennial-scale processes. Enriched δ(13)C-CO(2) during peak glaciation suggests increased ocean carbon storage. Variations in δ(13)C-CO(2) in early MIS 4 suggest multiple processes were active during CO(2) drawdown, potentially including decreased land carbon and decreased Southern Ocean air-sea gas exchange superposed on increased ocean carbon storage. CO(2) remained low during MIS 4 while δ(13)C-CO(2) fluctuations suggest changes in Southern Ocean and North Atlantic air-sea gas exchange. A 7 ppm increase in CO(2) at the onset of Dansgaard-Oeschger event 19 (72.1 ka) and 27 ppm increase in CO(2) during 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.