| Summary: | The Gulf of Alaska receives considerable freshwater discharge from rivers and streams along the mountainous coastlines of Southeast Alaska. On the shelf, the Alaskan Coastal Current (ACC) interacts with the freshwater outflow from the passages in Southeast Alaska. However, it is unclear whether the freshwater originating from the glacial fjords in Southeast Alaska is exporting a substantial fraction of nutrients to the greater Alaska Current. Nitrogen in particular is essential for living organisms and is a limiting nutrient for primary production in marine environments. Consequently, the bioavailability of nitrogen shapes planktonic diversity and influences regional food web structures and productivity. Here, we report measurements of the concentration and the δ15N of nitrate plus nitrite (NO3+NO2) from profiles collected within Glacier Bay and on the Southeast Alaska shelf and slope during August 2022. These measurements are evaluated in the context of additional samples collected in the Gulf of Alaska and North Pacific in August 2013 to characterize the NO3+NO2 isotopic composition of regional marine water masses. We evaluate salinity as a tracer for glacial meltwater to quantify the relative importance of freshwater and marine sources of NO3+NO2 to Southeast Alaskan coastal waters. Together, NO3+NO2 isotopic measurements and salinity allow us to evaluate freshwater nutrient export from the fjords to the coast and quantify the fjord's relative impact on NO3+NO2 in the Gulf of Alaska coastal system. nitrogen cycling, nitrogen isotopes, Gulf of Alaska, Glacier Bay National Park
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