Enhanced deoxygenation and carbon storage in the mid-depth subarctic Pacific during the Bølling-Allerød

Reconstructing changes in ocean carbon reservoir is essential for understanding how oceans regulate atmospheric carbon dioxide (CO₂) fluctuations. It has been considered that large amounts of CO₂ were released from the deep subarctic Pacific during the Bølling-Allerød (BA). However, this is inconsistent with the slowing or pausing of atmospheric CO₂ rise throughout the BA. On this issue, an increase of carbon storage in the mid-depth subarctic Pacific is speculated, more geological reconstructions are needed to confirm it. Here, we present magnetofossils and redox-sensitive trace elements records from core LV63–41–2 retrieved from the mid-depth western subarctic Pacific to reconstruct the paleo-redox conditions and carbon storage changes spanning the last deglaciation. The significantly increased proportion of elongated magnetofossils and the enrichment of authigenic U are identified during the BA, consistently indicating lower oxygen concentration in the overlying bottom water and sediment pore water. This BA deoxygenation was widespread across mid-depth subarctic Pacific areas and could reflect increased respired dissolved inorganic carbon storage. Furthermore, the low-oxygen sedimentary environment would facilitate more organic carbon to be buried in sediments. The increases in respired carbon storage and organic carbon burial in the mid-depth subarctic Pacific might have slowed BA atmospheric CO₂ rise. This study highlights the significant application value of magnetofossils in reconstructing paleo-redox conditions in the subarctic Pacific and points out the important role of the mid-depth subarctic Pacific in regulating atmospheric CO₂ fluctuations.