Impact of Atlantic Water and Subglacial Discharge on Marine-Terminating Glaciers: Insights from Field Observations and Numerical Modeling in Tempelfjorden, Svalbard

A reduction in sea ice extent and increasing temperatures have been linked to enhancement and shallowing of warm Atlantic Water (AW) advection into Isfjorden, a fjord on the west coast of Svalbard (Skogseth et al., 2020). With warming AW (Walczowski et al., 2017), there is an increased interest in how this affects the stability of marine-terminating glaciers (MTGs) (Skogseth et al., 2020), as an increase in water temperatures could lead to enhancing melt rates and therefore a destabilisation of MTGs (Luckman et al., 2015). Usually, sills protect the MTGs by blocking the pathway of AW into the fjord, however, with a shallowing of AW it can enter the fjord more easily. A better understanding of the circulation in fjords with MTGs is crucial in quantifying the effect of enhancement and shallowing of AW on MTGs.

In June 2023, data were collected aboard the RV Hanna Resvoll to measure temperature, salinity, turbulent kinetic energy dissipation, and velocities across the glacier front. High-resolution data were obtained using a Microstructure Profiler and a vessel-mounted Acoustic Doppler Current Profiler (ADCP). Two moorings were deployed to capture flow across the fjord sill.

A general-purpose hydrodynamic model (MITgcm) is used to investigate sensitivity of glacial melt to varying combinations of the inflowing water temperature, the depth of maximum temperature, tidal flows and sub-glacial discharge rate. The model was configured using realistic bathymetry from multibeam surveys on a 50m x 50m horizontal grid with 2m resolution in the vertical. Realistic tides were forced at the seaward boundary, the "iceplume" package (Cowton et al., 2015) was used to simulate glacial melt and sub-glacial discharge at the glacial terminus. The model is initialised and validated with the independent observational data set as described above. Additionally, simulations explore the combined impact of a deepening and warming AW layer, along with increased subglacial discharge plume.

These results provide critical insights into the future stability of MTGs in a warming climate and offer a more comprehensive understanding of how shifts in fjord circulation could enhance melt rates and further destabilize glacier fronts.