The Impact of Fjord-Glacier Geometry on Circulation and Renewal in Tidewater Glacier Fjords

The retreat of ice sheets is a leading cause of global sea-level rise, with much of this change due to accelerated flow of marine-terminating outlet glaciers. At the regional scale, neighboring glaciers often exhibit different mass balances – suggesting that local fjord and/or glacier dynamics may control individual glacier response. Recent work has demonstrated that meltwater flux at the grounding line drives a turbulent plume, which entrains warm bottom waters that increase submarine melt rates. However, we still lack an understanding of how fjord-glacier properties (grounding line depth, fjord width, and sill height) modulate the renewal of warm waters at the ice face. Here, we combine idealized ocean simulations and observations from two adjacent yet geometrically dissimilar fjords in west Greenland, to investigate how fjord-glacier geometry regulates the exchange and mixing of fjord waters with the continental shelf. Initial conditions are prescribed from observations collected in summer 2014. We run a suite of experiments varying meltwater flux, wind stress magnitude and direction, tidal forcing, and sill height. Our results, consistent with the field observations, indicate that buoyancy forcing from deeply-grounded glaciers results in diluted subsurface outflows that can draw deep waters over the sill and toward the glacier, while shallow fjords result in thin, surface-trapped plumes. We find that wind and tidal forcing strongly influence the background exchange flow. Passive tracers injected in the plume, fjord basin, and shelf waters are used to estimate turnover timescales. Our results highlight the importance of fjord-glacier geometry in dictating the dominant modes of fjord circulation.