Master Thesis Defence by Astrid Mørkholt Toft

Title: Dynamical response of the Greenland Ice Sheet to climate change

Abstract: 

Surface meltwater runoff is a major driver of mass loss from the Greenland Ice Sheet and plays a key role in modulating seasonal and inter‑annual ice flow variability. This study combines the PROMICE ice velocity maps from SAR imaging with RACMO2.3p2 runoff to investigate how meltwater supply influences ice dynamics across the ice sheet. This thesis consists of three complementary analyses—a flowline‑based assessment of seasonal timing, a 1 km x 1 km evaluation of acceleration changes surrounding the extreme melt year 2019, and an unsupervised K‑Means clustering of velocity time series. These analyses provide an extensive spatial characterization of ice–hydrology interactions.

Across most regions, earlier runoff onset and earlier runoff peaks correspond to earlier seasonal velocity peaks, while greater annual runoff is associated with earlier channelization and earlier acceleration. Dynamic responses to the 2019 melt season vary across the ice sheet, reflecting local differences in drainage efficiency and glacier geometry. The clustering analysis identifies four dominant seasonal velocity patterns that span a continuum from efficient to strongly melt‑sensitive, inefficient drainage regimes, with their spatial distributions depending on latitude, surface elevation, and melt intensity. 

Together, the results show that the Greenland Ice Sheet’s response to meltwater forcing is highly variable in space and time, governed by regionally distinct transitions between efficient and inefficient subglacial drainage systems. These findings highlight the importance of spatially extensive observations for understanding and projecting ice flow variability in a warming climate.

Supervisors: Christine Hvidberg and Anne Munck Solgaard (GEUS)