Isotopic and Geochemical Study of Organic Matter in Marine Sediments from the Indigirka Delta to the Ice Shelf Border of the East-Siberian Sea

Abstract

Various hydrocarbon gases (СН_4, С₂Н₄, С₂Н₆, С₃Н₆, С₃Н₈, С₄Н₈, n-С₄Н₁₀) and CO₂ have been extracted in low concentrations from different layers of marine sediments up to 2 m thick on the continental shelf of the East Siberian Sea along the profile from the mouth of the Indigirka River to the ice shelf border. A freshwater complex supplied by the Indigirka and other rivers has the dominant influence on the composition of organic matter (OM) in the almost entire studied area of the East Siberian Sea. Concentrations of most common gases CH₄ and CO₂ increase with increasing sampling depth in sediment core collected at station 5602-2, while the carbon isotopic composition of CO₂ decreases, reaching a value of –24‰. A sulfate reduction area was found at sediment depth of 48–70 cm. It was shown for the first time that the diagenesis of OM results in a systematic change in isotope fractional characteristics (IFC). IFC was obtained for the low-maturation OM, for OM from the sulfate reduction area, and for the high-maturation OM. OM in the low horizons of the sediment (below 77 cm from the surface) is much more evolved compared with the immature sediments of the upper horizons.