Distribution and sources of organic matter in surface sediments of the eastern continental margin of India

• Published in: Journal of geophysical research. Biogeosciences 2013-12, Vol.118 (4), p.1484-1494
• Main Authors: Krishna, M. S., Naidu, S. A., Subbaiah, Ch. V., Sarma, V. V. S. S., Reddy, N. P. C.
• Format: Article
• Language: English
• Subjects: Bay of Bengal; Brackish; Carbon; Coastal; Continental margins; Continental shelves; Crops; Detritus; Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Marine; Marine and continental quaternary; nitrogen isotopes; Organic carbon; Organic matter; River discharge; River flow; Rivers; sediment; Sediments; stable carbon; Stable isotopes; Sugarcane; Surficial geology; Terrestrial environments; Vegetation; Water column
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1002/2013JG002424

The sources and distribution of organic matter (OM) in surface sediments of the eastern continental margin of India, including the region influenced by river discharge, were investigated using content, molar C:N ratios and stable isotopes of carbon and nitrogen. Despite relatively high water column integrated chlorophyll‐a concentrations were found in the continental shelf than the slope; however, the lower sediment organic carbon (SOC) was found in the former than the latter region suggesting that in situ production did not play significant role on preservation of SOC in the coastal Bay of Bengal. The broad range of δ13C of SOC (−23.2 to −16.7‰) suggests that OM is a broad mixture of terrestrial and marine OM. Relative contributions from terrestrial C3 and C4 plants and marine sources are quantified as 34%, 23%, and 43%, respectively, indicating that dominant source of allochthonous OM (~57%) in the coastal Bay of Bengal. Relatively higher contribution of OM from C4 plants was found in the sediments at off river Krishna indicating that this region received detritus of agricultural crops such as jowar, bajra, and sugar cane, which are dominant in its drainage basin, during SW monsoon. This study revealed that relatively high OM preserved in the slope than shelf region along the coastal Bay of Bengal and the composition of OM is primarily controlled by the type of agricultural crops and vegetation in the drainage basin of the river. Key Points Preservation controls sediment organic carbon (SOC) rather than production SOC is dominated by terrestrial (57%) than marine organic matter (OM; 43%) Agricultural crops and vegetation controls terrestrial OM