Late Quaternary record of pteropod preservation from the Andaman Sea

In order to understand the glacial to interglacial fluctuations in pteropod preservation and productivity during the late Quaternary (∼ 54 ka BP to present), we investigated pteropod, organic carbon (Corg) and Globigerina bulloides abundance in a deep sea core from the western Andaman Sea. Pteropod abundance and preservation is similar to the “Indo-Pacific carbonate preservation type”, showing better preservation during glacial and poor preservation during interglacial periods. The core site appears to have remained below the aragonite compensation depth (ACD) throughout the Holocene, indicated by the total absence of pteropods. Maximum abundance and good preservation of pteropods was observed during stadials such as Younger Dryas (YD), Heinrich Events (HEs) and Last Glacial Maxima (LGM) indicating weaker oxygen minimum zone (OMZ) and deeper ACD. Furthermore, the high relative abundance of mesopelagic pteropods over epipelagic forms suggests a well ventilated water column with weak OMZ particularly during LGM, apparently driven by intense winter monsoon. Increased monsoon-driven productivity was observed during 45–40 ka, of early Marine Isotope Stage 2 (MIS 2, 24–22 ka), Bølling/Allerød (B/A; 15–13.5 ka), YD and late Holocene as evidenced by Corg content and G. bulloides. Enhanced pteropod preservation of H1 associated with low Corg content and G. bulloides suggests that reduced monsoonal driven productivity might have influenced pteropod preservation. Deglacial preservation spike in the Andaman Sea is consistent with other northern Indian Ocean records and elsewhere outside the Indian Ocean implying the event is global in nature, marked by deepening of ACD probably driven by enhancement of winter monsoon on local and changes in intermediate water circulation on regional scale.