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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. Plain Language Summary: The interaction between the Greenland Ice Sheet and the surrounding ocean is one of the key links in the regional climate system. Ocean heat melts the edges of the ice sheet, causing glacier speed‐up, retreat and sea level contribution. Meltwater from the ice sheet enters the ocean where it alters ocean properties and potentially ocean currents. This meltwater also drives upwelling of nutrients that can impact local ecosystems. All of these processes occur in long, deep and narrow fjords that connect the ice sheet and ocean. In this study, we present a first continent‐wide overview of the geometry and dynamics of Greenland's fjords. We combine recent bathymetric, atmospheric, and oceanographic datasets with a simple model to show that many fjords are well connected to the ocean in both bathymetry and circulation, suggesting that changes in the ocean on the continental shelf will be quickly transmitted to the ice sheet margin. We also suggest that meltwater from the ice sheet is rapidly mixed within fjords and will enter the wider ocean as a dilute subsurface mixture. This study is a step toward implementing fjord heat, freshwater and nutrient fluxes into large‐scale models that cannot resolve fjords. Key Points: We present a first ice sheet‐wide inventory of subglacial discharge‐driven upwelling plumes around the margin of the Greenland Ice SheetJust 0.02 Sv of subglacial discharge drives 0.6–1.6 Sv of upwelling that settles at 0–260 m depth and can renew most fjords within a summerFjords provide a path to the ocean deeper than 200 m for 82 out of 136 glaciers considered, suggesting warm waters reach most major glaciers [ABSTRACT FROM AUTHOR]

Recent acceleration of Greenland's ocean‐terminating glaciers has substantially amplified the ice sheet's contribution to global sea level. Increased oceanic melting of these tidewater glaciers is widely cited as the likely trigger, and is thought to be highest within vigorous plumes driven by freshwater drainage from beneath glaciers. Yet melting of the larger part of calving fronts outside of plumes remains largely unstudied. Here we combine ocean observations collected within 100 m of a tidewater glacier with a numerical model to show that unlike previously assumed, plumes drive an energetic fjord‐wide circulation which enhances melting along the entire calving front. Compared to estimates of melting within plumes alone, this fjord‐wide circulation effectively doubles the glacier‐wide melt rate, and through shaping the calving front has a potential dynamic impact on calving. Our results suggest that melting driven by fjord‐scale circulation should be considered in process‐based projections of Greenland's sea level contribution. Plain Language Summary: As the world warms, loss of ice from the Greenland Ice Sheet will be a significant source of sea level rise. Greenland loses ice partly through the flow of huge rivers of ice called tidewater glaciers that dump solid ice directly into the ocean. Over the past two decades, tidewater glaciers around Greenland have accelerated dramatically, increasing Greenland's contribution to global mean sea level. There is mounting evidence that these accelerations have been driven by ocean warming, and a resulting increase in the rate at which the ocean melts the front of tidewater glaciers (called submarine melting). Yet submarine melting is at present poorly understood, in part due to the danger and difficulty of collecting data close to tidewater glaciers. We present observations of the ocean in front of a tidewater glacier that are unprecedented in their proximity to the glacier. These data reveal an ocean circulation which flushes warm water along the front of the glacier, driving high rates of submarine melting. We then use a numerical model to identify what drives this circulation. Our results are an important step toward understanding a key process which will modulate future sea level contribution from the Greenland ice sheet. Key Points: Ocean observations that are unprecedented in their spatial detail and proximity to a Greenlandic tidewater glacier are reportedDespite being highly localized, plumes drive fjord‐wide circulation and hence glacier‐wide submarine melting at tidewater glaciersFjord‐scale submarine melting drives significant mass loss and may promote calving, hence is a key process determining glacier stability [ABSTRACT FROM AUTHOR]