Tracing the strength of the southwest monsoon using boron isotopes in the eastern Arabian Sea

Abstract

Here we present the first boron isotope-based pCO₂^sw (pCO₂ of seawater) reconstruction from the eastern Arabian Sea using the planktic foraminifera species Globigerinoides ruber. Our results from sediment core AAS9/21 show that pCO₂^sw varied between ~160 and 300 µatm during the last 23 kyr. The deltapCO₂, the sea-air pCO₂ difference, is relatively small during the last glacial maximum and becomes more negative towards the Holocene, with the exception of a significant excess during the last deglaciation centered on the Bølling-Ållerød. Throughout the record, deltapCO₂ is predominantly negative, probably as a result of enhanced biological productivity (and higher nutrient and carbon utilization) during the southwest monsoon. A reduction in deltapCO₂ during the last glacial maximum is therefore consistent with a reduction in the strength of this monsoon system.