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

Abstract

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 B & oslash;lling-Aller & oslash;d (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 lowoxygen 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.