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Abstract
Rates of polar glacial melting are accelerating with rising global temperatures; these increasingly large freshwater fluxes impact coastal marine ecosystems. The meltwater delivered to the coastal ocean can affect light and/or nutrient availability for phytoplankton, which can potentially influence rates of primary productivity. With three idealized modeling studies, I examined the controls on light and nutrient availability in these high-latitude regions receiving large fluxes of glacial meltwater. The first of these studies investigates the potential for extreme melt events of the Greenland Ice Sheet (GrIS) to impact light availability for phytoplankton offshore. I used a 1-D phytoplankton model informed by the mixed layer depths from a Regional Ocean Modeling System (ROMS) forced with subglacial runoff fluxes derived from a hydrological runoff model of the GrIS. The model shows that Greenland meltwater has the potential to extend the phytoplankton growing season into fall, and has the largest potential impact for light-limited primary production under lower-light conditions. The second study focuses on the intense phytoplankton bloom in the Amundsen Sea Polynya (ASP), which is the most productive of all Antarctic coastal polynyas. Observations from the polynya show that the ASP phytoplankton experience both light and iron stress. I used a 1-D light-, nitrate, and iron-limited phytoplankton model to investigate light and iron controls on primary productivity in the Amundsen Sea Polynya. The model suggests that light limitation from phytoplankton self-shading is most controlling for most of the bloom, and that combined light and iron limitation drive the bloom into decline. The third modeling study concerns the marine-terminating glacial fjords of Greenland, where meltwater discharged at depth can result in delivery of buoyantly-upwelled nutrient-rich water near the surface, where it may supply phytoplankton blooms. I used an idealized 3-D coupled physical-biogeochemical model of a fjord to investigate the fjord conditions best suited for export of these upwelled nutrients out of the fjord and onto the shelf. The model shows that shelf forcing, the discharge rate, and the discharge depth are the most important controls on the export of nutrients out of the fjord.