Examining the asynchronous behaviour of the Upernavik Isstrøm in northwest Greenland

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Voss, Kelsey
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The Upernavik Isstrøm, located in northwest Greenland, consists of five marine-terminating glaciers (referred to as U0 to U4, north to south) that have all been responding asynchronously to climate change. All five outlets share similar oceanic, atmospheric, and dynamic influences as they are geographically close, yet contrasting ice-flow behaviour was observed between outlets. This thesis presents a detailed analysis of the varying ice dynamics by updating the observational record of Upernavik’s outlets with recently derived satellite data, examining the role of floating ice tongues by evaluating a variety of proxies for floating ice, and modelling the drivers of ice-flow speed at the two fastest outlets, U1 and U2, with a recent flowline model, Icepack. We found recent patterns in floatation for U1 and U2 that indicated both outlets have new floating ice tongues that persisted through 2021. We evaluated four proxies of floating termini, including tabular iceberg calving, plume polynyas, hydrostatic elevation, and slope, and found only hydrostatic elevation and slope to be reliable proxies. While we initially hypothesized that floating ice tongues drove the acceleration of U1 and U2, our measured velocity data and modelled ice-flow sensitivity to changes in basal slipperiness, shear margin strength, thinning, and terminus retreat, showed ice-flow was realistically explained by changes in basal slipperiness. Icepack was capable of handling this complex case study and the simplified model provided great context regarding the forcings acting on Upernavik’s outlets. This strongly supports that U1 and U2 are seasonally and inter-annually controlled by subglacial hydrology. While the timing and magnitude of observed changes in thinning and retreat varies between outlets, all outlets displayed behaviour characteristic of glaciers controlled by meltwater availability at the bed. These results emphasize the importance of including subglacial hydrology in future studies of Upernavik and other marine-terminating glaciers to improve our understanding of how climate change may affect Greenland in the future.
Greenland, Glacier, Climate Change, Ice Flow, Meltwater, Ice Stream