Possible factors that control calcite dissolution in the western tropical Indian Ocean

Calcite dissolution in marine sediments is known to be driven by the degree of saturation state with respect to calcium carbonate, of overlying bottom waters. Three paleocarbonateion proxies, planktonic foraminifer size index, shell weight and calcite crystallinity applied to a set of core top samples reveal that calcite dissolution commences from 2250m onwards and intensifies at around 3900m water depth in the Western Tropical Indian Ocean 1. It was proposed earlier that carbonate dissolution can be caused due to acidification of pore water 2. It is shown that shell weights of the foraminifera species Pulleniatina obliquiloculata indicate that this intense dissolution observed at 3900m was caused due to undersaturation of CO3= in the bottom waters in the Indian Ocea

Sea surface temperture reconstruction and planktonic foraminifera of ODP Hole 117-723A

In the western Arabian Sea (WAS), the highest seasonal sea surface temperature (SST) difference presently occurs between May and August. In order to gain an understanding on how monsoonal upwelling modulates the SST difference between these two months, we have computed SST for the months of May and August based on census counts of planktonic foraminifers by using the artificial neural network (ANN) technique. 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 % could have been caused by the occurrence of a prolonged upwelling season (from May through July) and maximum difference in the incoming solar radiation between May and August. Overall, variations in the SST difference between May and August show that the timing of intense upwelling in the Western Arabian Sea over the last 22 kyr has been variable over the months of June, July and August

Evolution of productivity and monsoonal dynamics in the eastern Arabian Sea during the past 68ka using dinoflagellate cyst records

For the first time here we report the dinoflagellate cyst assemblage response to the monsoon variability over the last 68 ka from the Eastern Arabian Sea (EAS). Based on the cyst assemblage, five dinoflagellate cyst zones were established, corresponding to four Marine Isotopic Stages (MIS 1–4). An increased abundance of autotrophic Gonyaulacoid species (especially Spiniferites) during glacials (MIS 2 and 4) and late MIS 3 (~ 41.67 to 25.3 ka) reflects high productivity driven by strong winter convection during the Northeast monsoon. In contrast, their decreased abundance during MIS 1 and early MIS 3 (~ 58.6 to 42.87 ka) reveals decrease in productivity due to strong stratification caused by intense monsoon precipitation induced runoff from the Western Ghats and reduced light penetration driven by cloud cover. The variation in heterotrophic Protoperidinium species abundance could be related to variation in the Oxygen Minimum Zone (OMZ) intensity, with better preservation during intense OMZ in MIS 3 and the late Holocene (~ 3 ka onwards). Therefore, it is proposed here that the abundance of Protoperidinium can be used as an index of OMZ in the EAS