BOOK OF ABSTRACTS 131 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C Soil Organic Matter, Caustobiolites, and Biochar SL63 Molecular Composition of Dissolved Organic Matter on the Arctic Shelf as a Proxy of Carbon Cycling Change Irina V. Perminova1, Anna N. Khreptugova1, Sommer Starr2, Robert Spencer2, Andrey I. Konstantinov1, Igor P. Semiletov3,4,5 1 Lomonosov Moscow State University, Department of Chemistry, Leninskie Gory 1-3, 119991 Moscow, Russia, iperminova@gmail.com 2 Florida State University, National High Field Magnetic Lab, Tallahassee, U.S.A. 3 Pacific Oceanological Institute, Far-East Branch of the Russian Academy of Sciences, Vladivostok, Russia 4 National Tomsk State University, Tomsk, Russia 5 SakhSU, Sakhalin State University, Yuzhno‑Sakhalinsk, Russia Warming in the Arctic is occurring a factor of four faster than in the rest of the world. This is due to the Arctic “acceleration” connected to positive feedback of this region to climate change as a result of both huge discharge of buried carbon of thawing terrigenic permafrost and growing methane emission due to degradation of submerged permafrost. Steady input of poorly humified bioavailable carbon of permafrost into the pool of dissolved organic matter (DOM) of Arctic shelf seas might change molecular composition and properties of DOM bringing unknown ecological consequences. The objective of this work was to track the footprint of ancient organic carbon from thawing permafrost in the DOM pool of the Arctic shelf seas is an obligatory The sampling of seawater was conducted in three arctic seas - the Kara Sea, the Laptev Sea and the East-Siberian sea during the AMK-82 cruise of R/V Academician Mstislav Keldysh. Seawater samples were filtered through GF/F filters with 0.7 um and stored in the dark glass, the samples for DOM extraction (1-5 L) were acidified and isolated with a use of solid phase extraction on Agilent Bond Elut PPL cartridges. The samples were characterized with a use of optical spectroscopy, Fourier transform mass spectrometry and NMR spectroscopy. A total of 130 DOM samples were isolated and characterized. The FT ICR MS data show that CHO compounds dominated in the Kara Sea, while heteroatom-containing compounds dominated in the Laptev Sea and the East Siberian Sea. Analysis of a set of 109 analytical samples of DOM showed that the population density of the Van Krevelen diagram in the region referred to the chemotype of hydrolyzable tannins/ carboxyl rich alicyclic moieties (CRAM) accounted up to 60% of the total spectral intensity< whereas terpenoids, lignins and carbohydrates accounted for the residual 40%. The PCA analysis of the FT ICR MS data made it possible to identify a separate cluster of samples isolated from
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