The mechanism controlling air-sea CO2 exchange under different ocean circulation conditions, a case study from Iberian Margin

One of the critical features of deglaciations is the sudden increase in atmospheric CO₂ levels. Regulating the Pleistocene atmospheric CO₂ variations requires the involvement of oceanic carbon storage changes. However, the mechanisms and pathways for air-sea carbon exchanges remain elusive, partly resulting from the insufficiency of marine carbonate system proxy data with a robust age control beyond Termination I.

The deglacial CO₂ rise toward Marine Isotope Stage (MIS) 9e (Termination IV) started from 197.1 ppm to 300.7 ppm^[1], representing the highest natural atmospheric CO₂ recorded in the Antarctic ice cores over the past 800 ka^[2]. Our high-resolution carbonate system records from the Iberian Margin with a robust age control suggest an expansion of southern-sourced Glacial Antarctic Bottom Water at the onset of the deglaciation, followed by a net release of CO₂ from the Atlantic sector of the Southern Ocean. However, our results indicate a different ocean circulation pattern during Termination III, when atmospheric CO₂ increases by 85 ppm^[2]. Unlike Termination III, the north-sourced water seems to take a large proportion of the deep Atlantic Ocean during this period.

References:

[1] Nehrbass-Ahles, C. et al. (2020), Science vol. 369 1000–1005.

[2] Bereiter, B. et al. (2015), Geophys. Res. Lett. 42, 542–549.