Gas-Geochemical Features of Bottom Sediments in the Linear Depression Zone of the West Kara Stage

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Abstract

During the 89th cruise of the R/V Academic Mstislav Keldysh in 2022, sediment columns were sampled at stations 7441 and 7444 located in the southwestern part of the Kara Sea. Station 7444 was located on a large submeridional depression, under the bottom of which gas-saturated sedimentary strata were detected. Background station 7441 was located at a distance of 68 km from station 7444. For the sediments of the background station 7441, the ratio of hydrocarbon gases C1 / C2+ < 100 indicated their thermogenic nature. In the sediment at station 7441, the formation of the gas component in the sediment was due to degradation of OM and inflow of thermogenic gases, while in the sediment of station 7444 there was an inflow of biogenic gas, apparently, from permafrost. The average concentration of CH4 in the sediment of station 7444 exceeded the average concentration in the sediment of column 7441 by 700 times, and the average concentrations of CO2 in the sediment of stations 7444 and 7441 were comparable. A sulfate-methane transition zone (SMTZ) was detected at the 541–545 cm horizon of the sediment of station 7444, where sulfate concentration decreased to minimum values, CH4 and CO2 concentrations reached maximum values. The sulfur isotopic composition of δ34S in this region was +20.8‰. The biogenic nature of gas in the sediment of station 7444 was evidenced by low values of the carbon isotopic composition of CH4 (mean value δ13C(CH4) = –99.7‰), and high C1 / C2+ > 10000 ratio near the SMTZ.

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V. S. Sevastyanov

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Author for correspondence.
Email: vsev@geokhi.ru
Russian Federation, Moscow

V. Yu. Fedulova

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

E. A. Moroz

Geological Institute of Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

E. A. Krasnova

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences; Lomonosov Moscow State University

Email: vsev@geokhi.ru
Russian Federation, Moscow; Moscow

S. G. Naymushin

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

N. V. Dushenko

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

S. A. Voropaev

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

A. A. Dolgonosov

Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences

Email: vsev@geokhi.ru
Russian Federation, Moscow

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Supplementary files

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2. Fig. 1. Landfill topography (a) and map of sampling stations location (b) in the vicinity of station 7444. The hatching shows the projection of the gas front on the bottom surface. A-B - acoustic profiling line (see Fig. 2).

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3. Fig. 2. High-frequency acoustic profiling profile (2-12 kHz) along line A-B (see Fig. 1) with a pronounced ‘bright spot’ type anomaly fixing the gas front roof.

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4. Fig. 3. Vertical distribution of gases in the sediments of Vostok station. 7444 (a) and 7441 (b).

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5. Fig. 4. Vertical distribution of extracted OM in sediments of Vostok station. 7441 и 7444.

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6. Fig. 5. Variation of carbon isotopic composition of extracted OM with sediment depth of vv. 7441 and 7444.

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7. Fig. 6. Change in the shape of isotope-fraction curves of some horizons with sediment depth of stations 7441 (a) and 7444 (b).

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