On modelling of calving front positions at KNS, southwest Greenland

Abstract

<p>Outlet glaciers in Greenland experience a combination of seasonal and climate-driven change. In this study, we investigate the temporal evolution of the ice front position at Kangiata Nunaata Sermia (KNS), southwest Greenland. At this outlet glacier, a seasonal ice tongue forms almost every year in winter and breaks up in spring.<em> </em>The motion of the ice-ocean interface is one key driver of ice dynamics. Hence, it is important to understand and reconstruct terminus fluctuations. Utilizing the increasing availability of remote sensing data and deep learning algorithms, we accurately and frequently map the ice/ocean transition from optical satellite imagery. How can we incorporate that geometrical information of frontal positions into ice sheet models? The ice flow counteracts the mass loss due to iceberg calving and frontal melt. All those processes result in moving ice fronts over time. The interaction between ice flow and ice discharge is one challenge in combining observed ice front positions and modelling. We present two ways to include the geometric information of ice front positions into the Ice-sheet and Sea-level System Model (ISSM). In a first approach, we engage a level-set method to incorporate the derived calving front positions into the ice sheet model. By prescribing observed front positions, we ignore any physical basis of ice flow dynamics. However, the level-set method allows us to solve a differential equation continuous in time and space. Since we have to deal with observational gaps of ice front positions, not all stress changes caused by changing ice front positions might be resolved by this approach. In the second approach, we discuss physical drivers of terminus changes in more detail. We show parametrizations of calving and frontal melt depending on stress thresholds and subglacial water fluxes to reproduce the observed temporal evolution of the ice front position. The parametrization due to calving leads to ice loss velocities that are one order of magnitude higher than the one due to ocean melt. In the end, we want to combine both approaches to come up with an accurate parameterization of ice loss due to calving and melting, which fit observations and incorporate the physics of glacier flow.</p>