Nitrogen and carbon isotopic composition of marine and terrestrial organic matter in Arctic Ocean sediments:: implications for nutrient utilization and organic matter composition |
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| Institution: | 1. Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Qingdao 266100, China;2. College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China;3. Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, China;4. Institute of Marine Organic Geochemistry, Ocean University of China, Qingdao 266100, China;5. Department of Geological Sciences, University of Florida, Gainesville, FL 32611-2120, USA;1. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China;2. Byrd Polar Research Center, Ohio State University, Columbus, OH 43210, United States;3. V. I. Il''ichev Pacific Oceanological Institute, Russian Academy of Sciences, Vladivostok 600041, Russia;1. Department of Marine Research, Environmental Protection Agency, Taikos av. 26, LT-91222, Lithuania;2. State research institute Center for Physical Sciences and Technology, Savanori? av. 231, LT-02300 Vilnius, Lithuania |
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| Abstract: | Relationships between organic carbon, total nitrogen and organic nitrogen concentrations and variations in δ13Corg and δ15Norg are examined in surface sediments from the eastern central Arctic Ocean and the Yermak Plateau. Removing the organic matter from samples with KOBr/KOH and determining residual as well as total N shows that there is a significant amount of bound inorganic N in the samples, which causes TOC/Ntotal ratios to be low (4–10 depending on the organic content). TOC/Norg ratios are significantly higher (8–16). This correction of organic TOC/N ratios for the presence of soil-derived bound ammonium is especially important in samples with high illite concentrations, the clay mineral mainly responsible for ammonium adsorption. The isotopic composition of the organic N fraction was estimated by determining the isotopic composition of the total and inorganic nitrogen fractions and assuming mass-balance. A strong correlation between δ15Norg values of the sediments and the nitrate concentration of surface waters indicates different relative nitrate utilization rates of the phytoplankton in various regions of the Arctic Ocean. On the Yermak Plateau, low δ15Norg values correspond to high nitrate concentrations, whereas in the central Arctic Ocean high δ15Norg values are found beneath low nitrate waters. Sediment δ13Corg values are close to ?23.0‰ in the Yermak Plateau region and approximately ?21.4‰ in the central Arctic Ocean. Particulate organic matter collected from meltwater ponds and ice-cores are relatively enriched in 13C (δ13Corg=?15.3 to ?20.6‰) most likely due to low CO2(aq) concentrations in these environments. A maximum terrestrial contribution of 30% of the organic matter to sediments in the central Arctic Ocean is derived, based on the carbon isotope data and various assumptions about the isotopic composition of the potential endmembers. |
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