Late Quaternary record of Indian summer monsoon-induced stratification and productivity collapse in the Andaman Sea

Abstract

During each summer monsoon, the northeastern Indian Ocean receives a huge amount of rain and river discharge, resulting in strong stratification and prevalence of oligotrophic conditions. These water column changes impact upper ocean productivity which is reflected in the planktonic foraminifera distribution, providing an opportunity to study the effect of monsoon forcing and stratification history. Analogous to modern-day stratification, very intense water column stratification and productivity collapse were observed associated with Indian summer monsoon (ISM) evolution. This paper reports significant stratification events during MIS 3 (37.0 to 33 and 27 to 24?cal?ka), B�lling/Aller�d (B/A), early Holocene (10.0 to 8.0?cal?ka) and mid-Holocene (7.0 to 5.0?cal?ka) which slowly muted upwelling and productivity. The deglacial intensification of the ISM started in the early stages of the B�lling/Aller�d (B/A) followed by slight weakening during the Younger Dryas and regained strength during the early Holocene, coinciding with the highest summer insolation at 30�N. A progressive decline in the abundances of productivity and salinity proxies from 4.2 to 2.0?cal?ka suggests a gradual weakening of the ISM. The late Quaternary productivity variations in the Bay of Bengal and the Andaman Sea are primarily controlled by salinity-related stratification.