| Summary: | Climate change is expected to alter the input of nitrogen (N) sources in the Eastern Canadian Arctic Archipelago (ECAA) and Baffin Bay due to increased discharge from glacial meltwater and permafrost thaw. Since dissolved inorganic N is generally depleted in surface waters, dissolved organic N (DON) could represent a significant N source fueling phytoplankton activity in Arctic ecosystems. Yet, few DON data for this region exist. We measured concentrations and stable isotope ratios (δ15N and δ18O) of DON and nitrate (NO3−) to investigate the sources and cycling of dissolved nitrogen in regional rivers and at the sea surface from samples collected in the ECAA and Baffin Bay. Samples were collected during Leg 2a and 2b of the ArcticNet expedition aboard the Canadian Coast Guard Ship (CCGS) Amundsen from July 5th to August 15th of 2019. The concentration and δ15N of DON were measured as in Knapp et al. (2005). Total dissolved nitrogen (TDN) was oxidized to NO3− using recrystallized persulfate followed by measurement on a NOx analyzer by chemiluminescent detection (Braman and Hendrix, 1989). The δ15N of NO3 was determined using the denitrifier method (Weigand et al., 2016). References: Braman, R. S., and Hendrix, S. A. (1989). Nanogram Nitrite and Nitrate Determination in Environmental and Biological Materials by Vanadium(III) Reduction with Chemiluminescence Detection. Analytical Chemistry, 61, 2715–2718. Knapp, A. N., Sigman, D. M., and Lipschultz, F. (2005). N isotopic composition of dissolved organic nitrogen and nitrate at the Bermuda Atlantic Time-series Study site. Global Biogeochemical Cycles, 19(1). Weigand, M. A., Foriel, J., Barnett, B., Oleynik, S., and Sigman, D. M. (2016). Updates to instrumentation and protocols for isotopic analysis of nitrate by the denitrifier method. Rapid Communications in Mass Spectrometry, 30(12), 1365-1383.).
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