Shell weights of foraminifera trace atmospheric CO2 from the Miocene to Pleistocene in the central Equatorial Indian Ocean

Abstract

The Maldives Sea is a region dominated by the South Asian monsoon (SAM) and at present, a CO2 source to the atmosphere. Ti/Al elemental ratios from Site U1467 and U1468 recovered from the Maldives Sea show a gradual increase from ~12 Ma and indicate terrigenous inputs to this region associated with increasing wind intensity associated with initiation of the SAM. Shell weights of planktonic foraminifera, Globigerinoides trilobus have been used to understand variations in surface water carbonate ion concentration for the last 20 Ma. Shell weights show a good correspondence with global CO2 records and show heavier shell weights during the colder periods than compared to warmer intervals which reveals that the Maldives Sea behaved similar to other tropical oceanic regions in terms of its surface water carbonate chemistry. A significant decrease in CaCO3 wt.%, decrease in foraminifera shell weights and dissolution of spines along with an increase in organic carbon (OC%) towards 10.5 Ma is linked to the reduced carbonate deposition and increased productivity during monsoon which is a feature in all tropical sediment cores. Lower shell weights and dissolution features on foraminiferal shells were observed during periods of intense Oxygen Minimum Zone (OMZ) suggesting calcite dissolution due to an increase in bottom water CO2.