Mapping the evolution of marine carbon during the last deglaciation: δ13C perspectives on the deglacial ocean carbon cycle

The changes in the ocean circulation and biological pump played crucial roles in the rise in atmospheric CO₂ during the last deglaciation. However, our understanding remains limited regarding which processes―air-sea exchange, ocean circulation, and the biological pump―primarily influence the spatial dynamics of the oceanic carbon cycle. To address this knowledge gap, the present study compiles global stable carbon isotope (δ¹³C) records from various sources, including shallow and deep planktic, along with epifaunal and infaunal benthic foraminifera. The synthesis reveals a total increase of 0.37 ± 0.05 ‰ in marine δ¹³C values since the last glacial maximum. Of this increase, 68 ± 5 % is attributed to the response of the oceans in the southern hemisphere, while 32 ± 4 % is attributed to the northern hemisphere. By analyzing the difference between planktic and benthic foraminifera, a decreased vertical δ¹³C gradient (δ¹³C_sp–sb) is observed during the last deglaciation, indicating rapid carbon exchange between surface and deep waters during deglaciation. Additionally, the offset between the epifaunal and infaunal δ¹³C (δ¹³C_sb–db) provides insights into changes in productivity and bottom water oxygenation. Overall, the global synthesis suggests that the δ¹³C variation is largely controlled by ocean circulation in the northern hemisphere and at higher latitudes of the southern hemisphere, while primary production significantly influences subtropical regions. Furthermore, the δ¹³C confirms that the rise in atmospheric CO₂ during the first phase of Heinrich Stadial 1 (HS1) resulted from reduced primary production in subtropical regions along with strong ventilation in the second phase of HS1. Interestingly, the δ¹³C variations during the Younger Dryas (YD) suggest strong ventilation without evident changes in primary production. This four-dimensional dataset provides valuable insights into the transient changes in the ocean carbon cycle during deglaciation.