Inconsistent change in surface hydrography of the eastern Arabian Sea during the last four glacial–interglacial intervals

The eastern Arabian Sea is influenced by both the advection of upwelled water from the western Arabian Sea and winter convective mixing. Therefore, sediments collected from the eastern Arabian Sea can help to understand the long-term seasonal hydrographic changes. We used the planktonic foraminifera census and stable isotopic ratio (δ18O) from sediments drilled during the International Ocean Discovery Program Expedition 355 to reconstruct surface hydrographic changes in the eastern Arabian Sea during the last 350 kyr. The increased abundance of Globigerina bulloides suggests enhanced advection of upwelled water during the latter half of MIS7 and the beginning of MIS6, as a result of a strengthened summer monsoon. A large drop in upwelling and/or advection of upwelled water from the western Arabian Sea is inferred during the subsequent interval of MIS6, based on the rare presence of G. bulloides. The comparable relative abundance of Neogloboquadrina dutertrei, G. bulloides and Globigerinoides ruber suggests that during the early part of MIS5, hydrographic conditions were similar to today. The upwelling decreased and winter convection increased with the progress of the glacial interval. A good coherence between planktonic foraminiferal assemblage-based monsoon stacks from both the eastern and western Arabian Sea suggests a coeval response of the entire northern Arabian Sea to the glacial–interglacial changes. The glacial–interglacial difference in δ18Osw-ivc was at a maximum with 4–5 psu change in salinity during Termination 2 and 3, and a minimum during Termination 4. The significantly reduced regional contribution to the glacial–interglacial change in δ18Osw-ivc during Termination 4 suggests a lesser change in the monsoon.

UTILIZATION OF ANALYTICAL TECHNIQUE FOR EVALUATION OF 13CDIC IN GROUNDWATER USING EA-IRMS UNDER THE CONDITION OF VIETNAMESE LAB

As the demand of extraction and consumption of groundwater increases, its quality has been facing the issue of water contamination caused by industrial as well as domestic activities. Isotopic ratio analysis is a modern and effective technique widely used to trace the source of groundwater contamination. In this study, an analytical technique for carbon stable isotopic ratio of dissolved inorganic carbon in groundwater using elemental analyzer - isotopic ratio mass spectrometer was utilized under the condition in Vietnamese lab. As a result, correlation and calibration equations were established in which good reproducibility of the international standards was achieved with the value of first standard deviation less than 0.3 ‰ as well as the accuracy and precision of the measurements were obtained with errors less than 0.12 ‰. Based on these equations, 15 samples of groundwater collected from Cu Chi (Viet Nam) district were analyzed and calculated.