Eastern Arabian Sea CO2 outgassing during the last deglaciation and Holocene related to deep-water carbonate chemistry

Abstract

Glacial to interglacial changes in atmospheric CO2 are an intriguing part of carbon reorganization in the climate system and are estimated by investigating deep-water carbonate ion concentrations ([CO32−]). The scarcity of studies on [CO32−] in deep waters of the Indian Ocean and its role in the climate system inspired us to study the past carbonate ion variations from the eastern Arabian Sea (EAS). We analyzed B/Ca ratios, δ13C, and δ18O of epibenthic foraminifera Cibicidoides wuellerstorfi from three cores bathing in different water masses of the EAS to determine deep-water [CO32−] and ventilation, spanning the Last Glacial Maximum (LGM) to the Holocene. This study reveals the existence of stored CO2 in deep waters of the EAS during the LGM. We document two periods of rise in [CO32−] in deep waters, during the deglaciation and the mid–Holocene. The rise in [CO32−] during the deglaciation indicates the outgassing of stored glacial CO2 from deep waters via the Southern Ocean and through escape via intermediate waters of the EAS. The minor rise in [CO32−] during the mid-Holocene could be due to the release of CO2 from deep water through upwelling, caused by strengthening of southern hemisphere westerly winds since 5.3 ka.