Summary of Abstract Submission

Abstract Submission No. IO50-06-0003PresentationOral


Dharmendra Pratap Singh*1, R. Saraswat1, R. Nigam1, D. K. Naik1

1 National Institute of Oceanography, Goa, India


Biogenic aragonite is an integral part of the carbonate flux in marine system and its dissolution/preservation in sediments is governed by pH. The seawater pH is regulated both by direct diffusion of CO2 from the atmosphere or its release from the metabolic activity of organisms feeding on the organic matter. The increased metabolic activity, associated with high primary productivity, can also lead to the development of oxygen minimum zone (OMZ). Thus changes in aragonite compensation depth (ACD) are supposedly closely linked with OMZ intensity. Here, for the first time we assess the ACD in the southeastern Arabian Sea by using pteropod abundance in the surface sediments and use it to understand the effect of dissolved oxygen on ACD. A total of 80 spade core-top samples along seven latitudinal transects, covering the continental shelf, slope and abyssal region of the southeastern Arabian Sea were used. Pteropods were picked from coarse fraction (≥63 μm). In the southeastern Arabian Sea, pteropods are dominated by Limacina inflata, as reported earlier from other parts of the Indian Ocean. Based on the pteropod preservation, we report that in the southeastern Arabian Sea, ACD lies at a water depth of ~600 m, which matches with the chemically defined aragonite saturation depth. We further report that the ACD shoals from north to south. The increase in pteropod abundance in the outer shelf region coincides with the drop in dissolved oxygen concentration. The deeper limit of pteropod abundance however, lies in the center of the oxygen minimum zone. Therefore, we suggest that the pteropod abundance in the southeastern Arabian Sea is not always related with the lower dissolved oxygen. This first report of the pteropod based aragonite compensation depth estimates from the southeastern Arabian Sea will help in assessing future changes in ACD under the influence of anthropogenic green-house gas emissions.