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

Here we present the first boron isotope-based pCO2sw (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 pCO2sw varied between ~160 and 300 µatm during the last 23 kyr. The ΔpCO2, the sea-air pCO2 difference, is relatively small during the last glacial maximum and becomes more negative toward the Holocene, with the exception of a significant excess during the last deglaciation centered on the Bølling-Ållerød. Throughout the record, ΔpCO2 is predominantly negative, probably as a result of enhanced biological productivity (and higher nutrient and carbon utilization) during the southwest monsoon. A reduction in ΔpCO2 during the last glacial maximum is therefore consistent with a reduction in the strength of this monsoon system.

Naik S., Naidu P. D., Foster G. L. & Martinez-Boti M. A., in press. Tracing the strength of the southwest monsoon using boron isotopes in the eastern Arabian Sea. Geophysical Research Letters. Article (subscription required).


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