Onboard Large-Scale Isolation and Characterization of Three Reference DOM Materials from Siberian Arctic Shelf Marine Water.

The Siberian Arctic Shelf is undergoing major climate change in the Northern Hemisphere, heavily impacted by a massive release of dissolved organic matter (DOM) due to degradation of permafrost as a consequence of global warming. This work is devoted to the isolation of large quantities of DOM from the Kara Sea, the Laptev Sea, and the East Siberian Sea, located from west to east along the Siberian Arctic Shelf. The goal was to isolate Arctic marine water reference DOM materials, addressing the gap in the set of available reference DOM materials. Large volumes of marine water (500-700 L) were collected from the three target seas and processed using a large-scale solid-phase extraction (SPE) setup aboard the research vessel "Academic Mstislav Keldysh" to establish a detailed molecular characterization of current Arctic DOM. The DOM was extracted using Bondesil PPL bulk sorbent at loading ratios ranging from 1:50 to 1:30 (on a DOC basis). The yield of DOM was 2 g from the Laptev Sea, 1.4 g from the Kara Sea, and 1.0 g from the East Siberian Sea. Detailed molecular characterization of the SPE DOM samples was conducted using elemental analysis, ¹³C and¹H NMR spectroscopy, FT-ICR mass spectrometry, and optical spectroscopy. All methods revealed that the DOM fromthe Kara Sea in West Siberia had a more oxidized and aromatic character compared to the DOM from the Laptev Sea and East Siberian Sea located on the East Siberian coast. The two latter DOM samples were less oxidized and richer in aliphatic structures. The Kara Sea sample was dominated by oxidized hydrolyzable tannins, while the Laptev Sea and East Siberian Sea samples were enriched with lignins and terpenoids. Fluorescence spectroscopy revealed a blue-shift in the DOM spectra from west to east, which may be linked to a decrease in humic-like fluorescence. Comparison with established terrestrial reference materials, such as Suwannee River fulvic acid and Suwannee River natural organic matter, demonstrates that the three Arctic DOM isolates provide a distinctive and valuable reference for studying marine DOM biogeochemistry.