Molecular and Isotopic Characterization of DOM on the East Siberian Shelf, Arctic Ocean.

Barbara Deutsch1, Thorsten Dittmar2, Marcus Sundbom3, Igor Peter Semiletov4 and Christoph Humborg3,5, (1)Stockholm University, Baltic Sea Centre, Stockholm, Sweden, (2)University of Oldenburg, ICBM-MPI Bridging Group for Marine Geochemistry, Oldenburg, Germany, (3)Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden, (4)University of Alaska Fairbanks, Fairbanks, AK, United States, (5)Bolin Centre for Climate Research, Baltic Sea Centre, Stockholm, Sweden
The composition and fate of terrestrial dissolved organic matter (DOM) reaching the Arctic Ocean via the large Siberian rivers is still largely unknown, especially in a changing climate. This was a central research topic for the SWERUS-C3 expedition in 2014 with the Swedish research vessel Oden along the outer shelves of the Laptev, East Siberian and Chukchi Seas.

Water profiles from 51 stations, including two transects across the shelf-basin interface (water depths <40 to >2500m), were sampled during July–August. Salinity ranged from 24.7 to 34.9, and dissolved organic carbon (DOC) concentrations showed values between 46 and 312 µmol L-1. DOM was isolated from seawater by solid phase extraction (SPE). The carbon and nitrogen stable isotope ratios (δ13C and δ15N) of SPE-DOM ranged from -27.9 to -22.4‰ and -0.3 to 4.6‰, respectively. SPE-DOM was further analysed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate the DOM molecular composition and to identify degradation pathways along the gradients in salinity and DOC, for example changes in aromaticity or saturation within the DOM pool.

The presented data will largely contribute to the recent knowledge about the composition as well as the large-scale input and degradation patterns of terrestrial DOM in the Arctic Ocean.