IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 132 Soil Organic Matter, Caustobiolites, and Biochar Thursday, 27 August 2026 / Hall B the Lena River mouth in a set of samples from the Laptev Sea. This cluster was distinguished by the higher contribution of CHON and CHONS formulas, as well as peptide and carbohydrate chemotypes, which may indicate the presence of organic matter from permafrost, which originated from the Lena River runoff. The obtained results demonstrated the high discriminating ability of molecular descriptors in relation to the source of DOM. The molecular composition data were also used to find common and unique formulas for each region studied. The pool of common formulae reflects the specifics of the entire Arctic shelf. It was shown that it consisted mainly of CHO molecules, which may be associated with a high contribution of CRAM compounds - up to 70% of the total number of formulas. This indicates the dominance of conservative marine DOM structures in the general pool of the Arctic shelf DOM in the late autumn period. These same structures completely determined the character of the northern tip of the Laptev Sea. At the same time, the Lena River samples were characterized by the maximum number and variety of unique structures. Their composition was dominated by heteroatom-containing components, which may be due to the influx of buried permafrost organic matter. The Kara and East Siberian Seas occupied an intermediate position. 13C NMR data on the structural group composition confirmed the maximum contribution of aliphatic carbon atoms replaced by heteroatoms for the Lena River samples and the dominance of saturated aliphatic and alicyclic structures in the Laptev Sea and the East Siberian Sea. This is consistent with the maximum contribution of conservative CRAM structures to these regions. Thus, for the first time, the possibility of diagnosing the molecular specificity of biolabile components of permafrost against the background of stable carbon structures in marine waters was demonstrated. The obtained results also allowed us to define a pool of the Arctic Shelf DOM present in all three seas under study. Acknowledgement A part of this research was supported by the Budgetary Task 122040600057-3.
RkJQdWJsaXNoZXIy NDA4Mjc=