Date of Award

Summer 2021

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Annie Bourbonnais

Abstract

Climate change is expected to drastically alter the input of inorganic nitrogen (N) sources in the Eastern Canadian Arctic Archipelago (ECAA) with increasing discharge from glacial meltwater and permafrost thawing. Since dissolved inorganic N is generally depleted in surface waters, dissolved organic N (DON) could represent a significant source of nutrients limiting primary production in Arctic ecosystems. Yet, few DON data for this region exist. We analyzed stable isotopes (δ15N and δ 18O of DON and NO3-) to investigate dissolved nitrogen cycling in glacial rivers and marine surface samples collected in the ECAA during summer 2019. We used isotopic data to determine dissolved N sources as well as production and consumption processes. DON concentrations (0.54-11.61 μmol L-1) and δ15N of DON (-0.71-9.61 ‰) in the ECAA were variable between different locations, suggesting the occurrence of different processes. DON concentrations were low in most rivers (up to 4.89 μmol L-1). DON concentrations versus salinity fell along a mixing line between low DON riverine and higher DON marine end members. Thus, increased input from glacial meltwater in the ECAA could act to increase stratification and dilute the marine DON pool, ultimately affecting primary productivity. In regions of highest primary productivity, DON concentrations were inversely correlated with chlorophyll-a and the δ15N of DON, suggesting net DON consumption during these localized phytoplankton blooms. We derived an isotope effect of -6.9‰ during DON consumption. Our data helps establish a baseline to assess future change in nutrient regime for this climate sensitive region.

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