Subannual and Seasonal Variability of Atlantic-Origin Waters in Two Adjacent West Greenland Fjords

Plain Language Summary Greenland fjords provide a pathway for the inflow of warm shelf waters to glacier termini and outflow of glacially modified waters to the coastal ocean. Characterizing the dominant modes of variability in fjord circulation, and how they vary over subannual and seasonal time scales, is critical for predicting ocean heat transport to the ice. Here we present a 2-year hydrographic record from a suite of moorings in Davis Strait and two neighboring west Greenland fjords that exhibit contrasting fjord and glacier geometry (Kangerdlugssuaq Sermerssua and Rink Isbrae). Hydrographic variability above the sill exhibits clear seasonality, with a progressive cooling of near-surface waters and shoaling of deep isotherms above the sill during winter to spring. Renewal of below-sill waters coincides with the arrival of dense waters at the fjord mouth; warm, salty Atlantic-origin water cascades into fjord basins from winter to midsummer. We then use Seaglider observations at Davis Strait, along with reanalysis of sea ice and wind stress in Baffin Bay, to explore the role of the West Greenland Current and local air-sea forcing in driving fjord renewal. These results demonstrate the importance of both remote and local processes in driving renewal of near-terminus waters, highlighting the need for sustained observations and improved ocean models that resolve the complete slope-trough-fjord-ice system. Submarine melting of ice due to warm ocean waters has been implicated as a mechanism for the retreat and destabilization of marine-terminating glaciers worldwide. In Greenland, fjords provide an important connection between marine-terminating glaciers and warm subsurface waters located offshore. However, due to sparse ocean-glacier observations in these ice-choked systems, especially during winter months, we lack an understanding of how the large-scale circulation along Greenland's periphery influences near-glacier ocean temperatures. To address this, we present a 2-year mooring record from Davis Strait and two neighboring west Greenland fjords. Above the sill, fjord temperatures exhibit a clear seasonal cycle that is inherited from the continental shelf and slope. Below the sill, warming of fjord waters occurs more intermittently and is initiated when salty Atlantic-origin waters arrive at the fjord mouth. In summary, these novel observations allow for a better understanding of ocean-glacier interactions in Greenland.