Climate change impacts ecosystem function and carbon (C) cycling in marine waters in the Arctic. In response to global warming, sea ice and ice sheets are melting, and Arctic River C output is increasing, causing the Arctic Ocean to become a mixing zone for diverse dissolved organic matter (DOM) that gets funneled through the Fram Strait before circulating around the world. Thus, the Fram Strait is poised to dramatically impact marine surface, bottom waters, and atmospheric carbon dioxide (CO₂) reservoirs upon DOM mineralization through natural processes. The new DOM exiting the Arctic Ocean may be highly influential to local, regional, and distant surface biological processes and may participate in abiotic transformations (e.g., photo-degradation), sink to the ocean floor, and/or be carried great distances with the thermohaline circulation. It is crucial to expand beyond measuring C quantities and determine C qualities to better understand its reactive potential. We used two advanced analytical chemistry techniques to describe the chemical characteristics of DOM at the molecular level, Nuclear Magnetic Resonance (NMR) spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). As a function of water mass and depth profile, Arctic Ocean DOM molecular characterization revealed various chemical species characterizable by FT-ICR MS; both surface water masses (Polar and Atlantic) contain more bioavailable DOM, and Atlantic water was characterized by in-situ marine biological production. Heterogeneity was more pronounced in the Polar Waters vs. the Atlantic waters. Major chemical classes included molecular composition with C_cH_hO_o and N- and/or S- containing C_cH_hO_o species, and average DOM masses increased with depth. Polar water masses contained more aromatic DOM than Atlantic, a result we expected with more lignin-like DOM in the Polar water; the lignin-like DOM character reflects the Arctic River C inputs. Both 1H NMR signals reflect inherent averaging from overlapping signals, but few sharp/high-intensity signals and varying abundances of chemical bonds were observed for the two water masses. The relative abundance of each chemical group will be determined by NMR and FT-ICR MS in our complementary analyses. We anticipate increases in DOM signatures resembling terrestrial lignin (lignin-like) composition and a decrease in surface water aromatic as sea ice thickness and extent decrease.

Juliana D'Andrilli

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