Hydraulic control of the submarine glacier melt in Greenlandic sill fjords

The oceanic forcing of basal melt remains a major source of uncertainty in climate ice sheet modelling.
Several factors such as ice and fjord geometry, ambient water properties and subglacial discharge in-
fluence the submarine melt processes. We use a high resolution, non-hydrostatic configuration of the
Massachusetts Institute of Technology general circulation model (MITgcm, see Wiskandt et al., 2022)
to investigate the dependence of basal melt rates and melt driven circulation in the Sherard Osborn
Fjord (SOF) under the floating ice tongue of Ryder Glacier (RG), northwest Greenland, on the fjords
bathymetry in connection with variable subglacial discharge. In SOF, a sill in front of the floating ice
shields the cavity underneath the ice from warm Atlantic water (AW) penetrating towards the grounding
line, providing an effective shielding of the glacier from oceanic thermal forcing. The volume flux of the
AW inflow is controlled by the sill height and the melt water outflow. The outflow volume flux is in turn
dependent on basal melting, subglacial discharge and the mixing of the two with the AW. For sufficiently
strong outflow, hydraulic control at the sill crest can limit the available glacier–ward flux and therefore
the available oceanic thermal forcing for basal melting creating a stabilizing feedback. In this study
we investigate the sensitivity of the AW inflow into an idealized fjord to the presence of a sill, variable
sill height and seasonal forcing from subglacial discharge. The model results are compared to theory of
hydraulic control (Nilsson et al., 2022).

References
Nilsson, J., van Dongen, E., Jakobsson, M., O’Regan, M., and Stranne, C. (2022).
Hydraulic suppression of basal glacier melt in sill fjords. EGUsphere, 2022:1–33.
Wiskandt, J., Koszalka, I. M., and Nilsson, J. (2022). Basal melt rates and ocean
circulation under the Ryder Glacier ice tongue and their response to climate warming: a high resolution
modelling study. EGUsphere, 2022:1–29.