Distribution and Source of Organic Matter in Cored Sediments From the Andaman Sea off Myanmar

H.M. Zakir Hossain, Jashore University of Science and Technology, Department of Petroleum and Mining Engineering, Jashore, Bangladesh, Hodaka Kawahata, University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan and Yoshikazu Sampei, Shimane University, Department of Geoscience, Matsue, Japan
Knowing the distribution, and source of sedimentary organic matter (OM) in the Andaman Sea off Myanmar, the second highest sink of organic carbon in the global ocean, is significant for understanding its biogeochemical cycle. In order to better establish these parameters, we determined the total organic carbon (TOC), total nitrogen (TN), total sulfur (TS), δ13Corg and δ15Ntot, and n-alkanes contents of multi-core surface sediments. TOC and TN concentrations varied from 0.61 to 1.18 wt.% (average 0.87 wt.%) and 0.07 to 0.17 wt.% (average 0.13 wt.%), respectively, with high TOC in the clay-rich sediments indicating that hydrodynamic sorting readily controlled TOC abundances. Bulk TOC/TN ratio (5.51 to 11.92, average 7.89) is attributed to the high inputs from planktonic sources of OM and appreciable amounts of terrestrial OM. The δ13Corg and δ15Ntot values for the sediment cores ranged from -8.34 to -20.3‰ and +3.65 to +6.53 ‰, respectively suggesting that OM in the sediments is largely derived from planktonic sources, with significant contributions from a mixture of terrestrial and aquatic sources and sea grasses. n-Alkane distributions are characterized mainly by C16 to C35, with odd-over-even predominance after C25, suggesting a diverse origin of land plant OMs. The relatively high content of odd long-chain n-alkanes from C27 to C33, with high peaks at C29 and C31, were detected in most investigated samples, reflecting a terrigenous origin of OM (e.g. shrubs, woody or herbaceous plants). Average chain length (ACL), carbon preference index (CPI), Paq and Pwax ratio values indicate that high input of OM from non-emergent aquatic macrophytes followed by grasses and herbs.