Characterization of Organic Matter in Sediment Cores of the Bay of Bengal, Andaman Sea and Indian Ocean

Total organic carbon (TOC), total nitrogen (TN), total sulfur (TS) and their ratio values were determined for 53 clay samples from 7 short sediment cores from the Bay of Bengal, Andaman Sea and Indian Ocean to decipher the concentration and source of organic matter (OM). High TOC content (>1%) was observed in cores of MY-3, and MY-7, whereas low content (<0.5%) was found in cores of BA-3, MY-5 and NR-1, with values ranging between 0.20 and 1.18 wt%. Similar to TOC, sediment TN content also exhibited clear differences in the Bay of Bengal, Andaman Sea and Indian Ocean. The Andaman Sea sediment contains relatively high TN content (0.17 wt.%), followed by the Bay of Bengal (<0.14 wt.%) and Indian Ocean (<0.08 wt.%). Core MY-5 in the Andaman Sea has relatively low (0.02 wt.%) and uniform distribution in TN content. All samples showed lower C/N ratios (5.3-11.9) and indicated a little input of terrestrial OM. The sediment TS content for Core MY-5 in the Andaman Sea was 0.10 wt.%, which was significantly much lower than that in the Bay of Bengal and other Andaman Sea sediment cores, but TS in the Indian Ocean was not found. More abundant TOC and TN in most core sediments from the Andaman Sea than those from the Bay of Bengal and Indian Ocean reflect a higher production of planktonic OM in this area. Clear peaks of C/S ratios in the cores from the Andaman Sea (27.8 at 10 cm in MY-3, 20.7 at 10 cm in MY-6, 22.3 at 18 cm in MY-7 and 13.1 at 6 cm in MY-11) suggested oxic events in the sea.