Multi-temporal Evolution and Collapse of Midgaard Glacier, Southeast Greenland from the Little Ice Age to the Present.

The Greenland Ice Sheet is one of the main contributors to sea-level rise, holding the equivalent water volume of 7.4m of global sea-level rise and losing mass at an accelerating rate. Southeast Greenland, especially the Sermilik Fjord has been a place of large dynamic changes over the last 100 years. Midgaard Glacier, east of Helheim Glacier, is showing some of the most distinct changes of the Greenland Ice Sheet, with a mass loss increasing from 41+/-17 Gt/y to 286+/-20 Gt/yr during the last thirty years. Despite these dramatic changes Midgaard Glacier has hitherto received little scientific attention.

In this study, we used a combination of satellite and aerial imagery to understand and determine dynamic glacier fluctuations in the Sermilik region between the Little Ice Age and the present. We monitored changes in surface elevation using oblique aerial images from 1933, declassified CORONA Satellite Photographs (1966), NASA's Landsat 1 Satellite images (1970s), aerial orthophotographs and digital elevation model (DEM) from the Agency for Data Supply and Efficiency (SDFE, 1981), Soviet Soyuz satellite KFA-1000 images (1992), SPOT (IPY) satellite images (2008), DEM and orthophotographs from SPOT-6/-7 (2016 ) and Worldview DEM from ArcticDEM (2011 to 2017). We used Structure-from-Motion techniques to reconstruct the former glacier surface elevation of the main outlet glaciers. We examined the complex marine-terminating glacier system in this area which includes Midgaard Glacier and also four major glaciers in its immediate vicinity. The dense record of DEMs were combined with a history of surface flow velocities since the 1980s, which was produced using a normalized cross-correlation technique over optical and synthetic aperture radar data.

We documented acceleration and significant thinning across the entire study area, along with the substantial collapse of the glaciers' fronts of both Midgaard Glacier and Glacier de France. We show that Glacier de France experienced an increased rate of retreat throughout the entire study period, while Midgaard Glacier retreated to such an extent as to become extinct.

Finally, we compared the glacier changes in volume and dynamics to the climate conditions in Southeast Greenland since the end of the LIA and conclude on the drivers of the retreat of Midgaard Glacier. Our work contributes to constraining the long-term mass loss of glaciers in the region and importantly highlights the importance of considering long-term ice dynamics when interpreting modern glacial changes.