Greenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two‐thirds of the glaciers. Our study provides a first pan‐Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet‐wide upwelling fluxes. This analysis provides important context for site‐specific studies and is a step toward implementing fjord‐scale heat, freshwater and nutrient fluxes in large‐scale ice sheet and climate models.

In July 2012, the surface of the Greenland Ice Sheet (GrIS) melted to an extent unprecedented over the last 100 years; we questioned the potential for such an extreme melt event to impact marine phytoplankton offshore. We hypothesized that stratification from meltwater could reduce light limitation for phytoplankton, and used a suite of numerical models to quantify the impact for 2003–2012. Because much of the 2012 meltwater discharged from southern Greenland, our study focused on the southwestern and southeastern coasts of Greenland, and the Labrador Sea. A 1‐D phytoplankton model used output from a Regional Ocean Modeling System (ROMS) coupled with a Regional Climate Model and a hydrological model of meltwater from runoff sources on the ice sheet, peripheral glaciers, and tundra. ROMS was run with and without meltwater to test the sensitivity of phytoplankton photosynthetic rates to the meltwater input. With meltwater, the pycnocline was shallower during late summer and early fall and thus light limitation on photosynthesis was reduced. Averaged over all years, added meltwater had the potential to increase gross primary production by 3–12% in the summer (July–August), and 13–60% in the fall (September–October). This meltwater effect was amplified when light was more limiting, and thus was greatest in the fall, under cloudier conditions, with higher self‐shading, and with more light‐sensitive phytoplankton groups. As the GrIS melt is projected to increase, late summer primary production in this region has the potential to increase as well, which could constitute an important biosphere response to high‐latitude climate change.

The Amundsen Sea Polynya (ASP) is distinguished by having the highest net primary production per unit area in the coastal Antarctic. Recent studies have related this high productivity to the presence of fast‐melting ice shelves, but the mechanisms involved are not well understood. In this study we describe the first numerical model of the ASP to represent explicitly the ocean‐ice interactions, nitrogen and iron cycles, and the coastal circulation at high resolution. The study focuses on the seasonal cycle of iron and carbon, and the results are broadly consistent with field observations collected during the summer of 2010–2011. The simulated biogeochemical cycle is strongly controlled by light availability(dictated by sea ice, phytoplankton self‐shading, and variable sunlight). The micronutrient iron exhibits strong seasonality, where scavenging by biogenic particles and remineralization play large compensating roles. Lateral fluxes of iron are also important to the iron budget, and our results confirm the key role played by inputs of dissolved iron from the buoyancy‐driven circulation of melting ice shelf cavities (the “meltwater pump”). The model suggests that westward flowing coastal circulation plays two important roles: it provides additional iron to the ASP and it collects particulate organic matter generated by the bloom and transports it to the west of the ASP. As a result, maps of vertical particulate organic matter fluxes show highest fluxes in shelf regions located west of the productive central ASP. Overall, these model results improve our mechanistic understanding of the ASP bloom, while suggesting testable hypotheses for future field efforts.

As mass loss from the Greenland Ice Sheet accelerates, this modeling study considers how meltwater inputs to the ocean can impact marine ecosystems using a simplified fjord scenario. At marine‐terminating glaciers in Greenland fjords, meltwater can be delivered far below the sea surface, both as subglacial runoff (from atmosphere‐driven surface melt) and as basal melt (from ocean heat). Such delivery can result in buoyancy‐driven upwelling and the upward entrainment of nutrient‐rich deep water, which can support phytoplankton growth in fjord surface waters. For this study, we use an idealized fjord‐scale model to investigate which properties of glaciers and fjords govern the transport of buoyantly upwelled nutrients from fjords. We model the influence of fjord geometry, hydrology, wind, tides, and phytoplankton growth within the fjord on meltwater‐driven nutrient export to the ocean. We use the Regional Ocean Modeling System (ROMS) coupled to a buoyant plume model and a biogeochemical model to simulate physical and biogeochemical processes within an idealized tidewater glacial fjord. Results show that meltwater‐driven nutrient export increases with larger subglacial discharge rates and deeper grounding lines, features that are both likely to change with continued ice sheet melting. Nutrient export decreases with longer residence times, allowing greater biological drawdown. While the absence of a coastal current in the model setup prevents the downstream advection of exported nutrients, results suggest that shelf‐forced flows could influence nutrient residence time within fjords. This simplified model highlights key uncertainties requiring further observation to understand ecological impacts of Greenland mass loss.

Coastal waters in the Labrador Sea are influenced by the seasonal input of meltwater from the Greenland ice sheet, which is predicted to more than double by the end of the century. Mechanisms controlling the offshore export of meltwater can have a significant effect on stratification and vertical stability in the Labrador Sea, being particularly important if the meltwater is transported toward the interior of the basin where winter convection occurs. Here we use a high‐resolution ocean model to show that coastal upwelling winds play a critical role transporting the meltwater offshore to about 150 km from the coast, where increased eddy activity and mean circulation can then transport the meltwater farther offshore. While meltwater discharged from West Greenland is either transported to Baffin Bay or circumnavigates the basin flowing mostly along isobaths, meltwater from East Greenland can reach the interior of the basin where it may influence stratification and winter convection whenever winds are anomalously upwelling favorable in late summer and early fall.