High temporal and spatial resolution inverse modeling of mélange rheology at Helheim Glacier, southeast Greenland

Abstract:

The calving of icebergs is responsible for a significant proportion of annual mass loss from marine-terminating glaciers and is believed to be a major factor in the rapid demise of paleo-ice sheets. Iceberg calving indirectly influences buttressing against the ice flow by controlling the structure and extent of ice mélange. This mixture of icebergs and seasonal sea ice that forms at the ice-ocean interface of many fast flowing outlet glaciers is believed to have an important influence on the flow of outlet glaciers. However, its physical properties are not well understood and there is disagreement about how to represent it in models. With recent forecasts anticipating that the majority of mass loss from the Greenland Ice Sheet will be dynamic in origin over the next two centuries, improving understanding of the mélange is key. We applied stereo digital photogrammetric methods to a high temporal and spatial resolution time series of time-lapse imagery to generate velocity fields and elevation models of the terminal region and ice mélange of Helheim glacier in Greenland’s southeast. For the first time, we use an inverse method implemented in an ice sheet model to determine the spatial pattern of mélange rheology that is consistent with the velocity fields. We explore the variation of the rheology pattern through time to identify areas that support higher stresses and thus provide greater buttressing.