Sea surface temperature changes during May and August in the western Arabian Sea over the last 22kyr: Implications as to shifting of the upwelling season

Abstract

In the modern day the highest seasonal sea surface temperature (SST) difference has been noticed between May and August in the western Arabian Sea. In order to gain an understanding on how the monsoon upwelling has modulated the SST difference between these two months, we have computed SST based on census counts of planktonic foraminifers by using the artificial neural network (ANN) technique for the months of May and August. The SST difference between May and August exhibits three distinct phases: i) a moderate SST difference in the late Holocene (0-3.5 ka) is attributable to intense upwelling during August, ii) a minimum SST difference from 4 to 12 ka is due to weak upwelling during the month of August, and iii) the highest SST difference during the last glacial interval (19 to 22 ka) with high Globigerina bulloides % would be caused by prolonged upwelling season from May through July and maximum difference in the incoming solar radiation between May and August. On the whole, the variations in the SST difference between May and August reveal that the occurrence of intense upwelling has been shifting among the months of June, July and August, over the last 22 ka in the Western Arabian Sea.