ORGANIC CARBON IN SURFACE SEDIMENTS OF LAPTEV SEA AND EAST SIBERIAN SEA: OBSERVATION OF PYROLYSIS DATA

Ongoing global warming accelerates release of relict terrigenous organic carbon from permafrost onto the Arctic shelf waters. When trans-ported in the land-sea system, it can further be accumulated in bottom sediments in the shelf or deep-sea zone and undergo degradation and remineralization, which leads to critical environmental consequences. This study aims at assessing the sources and degradation de-gree of terrigenous organic matter in the surface sediments of the Eastern Arctic seas. Within this study, marine bottom sediments taken from the surface horizon (0-10 cm) were investigated. Sampling was carried out during the 2011-2019 marine research expeditions. La-teral consistency of hydrogen index values in modern marine sediments on the Eastern Arctic shelf (mainly in the Laptev Sea) is associat-ed with the great contribution of heterogeneous biolabile terrestrial organic matter, in contrast to other Arctic waters, where growing hydro-gen index values are associated with the consistently growing contribution of autochthonous organic matter with increasing distance from the coast. While considering the d13C and HI/OI correlation, there are also significant deviations from the linear dependence which usually indicates a conservative marine geochemical regime. Sediments of the Buor-Khaya Bay are characterized by an increased HI/OI values in contrast to the deep-water sediments of the continental slope which shows lower hydrogen content and a higher proportion of oxygen -containing compounds, indicating a strong transformation of organic matter. These findings confirm a key role of terrigenous supply in spe-cific biogeochemical conditions in the studied area and reveal that geochemical indicators of immature organic matter sources in the East-ern Arctic seas should be interpreted differently from other Arctic continental margins.