Abstract
<p>The East Siberian Arctic Shelf (ESAS), the world’s widest and shallow continental shelf, plays a crucial role in the climate system of our planet holding huge amounts of organic carbon (OC) in the permafrost deposits which are remobilized upon accelerating permafrost thaw. To get more detailed insights into the sources of OC and compare the mechanisms of its transformation in the different ESAS zones, we investigate a scarcely studied coastal area of the East Siberian Sea – Chaun Bay (CB), a semi-closed accumulative area, where the influence of river discharge is limited and the coastline deposits are composed mainly of the rocky formations, which is contrasting to the permafrost-dominated Arctic bays.</p><p>In this study, we analyzed  25 surface sediments collected along the profile from the coastal zone of CB to the midshelf of East Siberian Sea. To characterize the OC composition, we used Rock-Eval indicators along with traditional molecular markers (n-alkanes; n-alkanoic acids). Detailed grain size composition was also performed in order to assess the sedimentation environment operating in the study area.</p><p>Sediments are mostly represented by sortable silt (7.61-62.48% on average 43.5%), fine silt (1.98-60.9% on average 34.63%) with a certain proportion of clay (average 11.13%) predominantly in the inner shelf areas, and sand (average 10.73%) deposited in the eastern, southern, and western (Aion Island) parts of the CB.</p><p>OC content along the studied profile ranged from 0.49 to 1.76%. Hydrogen index along the studied profile ranged from 111 to 232 mg/g, Oxygen index varied from 134 to 239 mg/g. The relationship between HI and OI indicated roughly equal contributions of terrestrial and marine sources to the OC composition. Meanwhile, variable distribution of n-alkanes is observed with a pronounced presence of high-molecular-weight n-alkanes, which are recognized as higher terrestrial vegetation markers. These data will be further combined with more detailed biomarker analysis to reveal the OM sources proportions in the CB sediments and to understand the dominating mechanisms of OC transformation within this area.</p><p>This analytical studies were financially supported by RSF (Project # 21-77-00075).</p>
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