Isotopic and geochemical study of marine sediments organic matter from delta of Indigirka river to the ice shelf border of the East-Siberian sea

Various hydrocarbon gases (СН 4,  С 2 Н 4 , С 2 Н 6 , С 3 Н 6 , С 3 Н 8 , С 4 Н 8 , н-С 4 Н 10 ) and CO 2  have been obtained with very low concentration from different layers of marine sediments with thickness up to 2 m on the continental shelf of the East Siberian Sea in the section from the mouth of Indigirka river to the ice shelf border. A freshwater complex, carried by Indigirka river and other rivers, has the dominant influence on composition of organic matter (OM) in almost entire studied area of the East Siberian Sea. It was shown that concentration of the most common gases CH 4  and CO 2  increases with increasing depth of sediment sampling for the core of sediments selected at station 5602-2, and the carbon isotope composition of CO 2  decreases, reaching a value of -24‰. A sulfate reduction area was found at sediment depth of 48–70 cm. For the first time it was shown that a regular change in isotopic fractional characteristics (IFC) occurs as a result of diagenesis of OM. IFC was obtained for low maturation OM, OM for sulfate reduction area, and for high maturation OM. For low horizons of the sediment (below 77 cm from the surface), the OM is significantly matured along the path of geochemical evolution compared with the immature sediments of the upper horizons.