Evidence for late-glacial oceanic carbon redistribution and discharge from the Pacific Southern Ocean

Southern Ocean deep-water circulation plays a vital role in the global carbon cycle. On geological time scales, upwelling along the Chilean margin likely contributed to the deglacial atmospheric carbon dioxide rise, but little quantitative evidence exists of carbon storage. Here, we develop an X-ray Micro-Computer-Tomography method to assess foraminiferal test dissolution as proxy for paleo-carbonate ion concentrations ([CO32-]). Our subantarctic Southeast Pacific sediment core depth transect shows significant deep-water [CO32-] variations during the Last Glacial Maximum and Deglaciation (10-22 ka BP). We provide evidence for an increase in [CO32-] during the early-deglacial period (15-19 ka BP) in Lower Circumpolar Deepwater. The export of such low-carbon deep-water from the Pacific to the Atlantic contributed to significantly lowered carbon storage within the Southern Ocean, highlighting the importance of a dynamic Pacific-Southern Ocean deep-water reconfiguration for shaping late-glacial oceanic carbon storage, and subsequent deglacial oceanic-atmospheric CO2 transfer. Evaluation of foraminiferal test dissolution by Computed Tomography scanner provided deep seawater carbonate ion concentration at the Southern Ocean. Quantitative data highlighted the reconfiguration of glacial to deglacial carbon storage followed by oceanic-atmospheric CO2 transfer.

Automated summary

The study reveals significant variations in carbonate ion concentrations in the Southern Ocean deep water during the Last Glacial Maximum and Deglaciation, using an X-ray Micro-Computer-Tomography method. The findings suggest that the export of low-carbon deep water from the Pacific to the Atlantic significantly reduced carbon storage in the Southern Ocean. This highlights the importance of Pacific-Southern Ocean deep-water reconfiguration for late-glacial oceanic carbon storage and subsequent deglacial oceanic-atmospheric CO2 transfer.