Influence of marginal highs on the accumulation of organic carbon along the continental slope off western India

Abstract

Twenty five surficial sediment samples were collected from the central western continental margin of India, which consists of diverse physiographic entities, continental slope, shelf margin basin, marginal high, and the deep Arabian Basin, at depths between 250 and 2050 m. The sediments were studied to assess the relative importance of productivity, oxygen minima, grain size and bathymetry on organic carbon accumulation/preservation. The total organic carbon (TOC) content in the study area varies from 0.70 to 5.86%. Highest values of organic carbon are recorded on the marginal highs (5.12–5.86%), followed by shelf margin basin (3.53–4.22%) and the continental slope (1.80–3.84%). The organic carbon content is relatively low in the Arabian Basin (0.98–1.46%). The sediments from marginal highs are characterized by high OC contents relative to upper slope at equivalent water depth and also the deeper shelf margin basin. The elevated organic carbon concentrations on marginal high and upper slope are associated with coarse-grained biogenic sediments while those in the shelf margin basin with fine-grained silty clays. The enrichment of organic carbon on the marginal highs is attributed to productivity-related biogenic sediments and their faster burial. It is surmised that diverse topographic features in the slope and the associated hydrodynamic processes also play an important role in the enrichment of organic carbon.