| Mass loss from the Greenland Ice Sheet has accelerated throughout the last decade, predominantly due to a quadrupling of ice discharge by iceberg calving, submarine melting, and meltwater runoff at marine-terminating outlet glaciers. The recent acceleration has been linked to the transport of increasing amounts of meltwater, fuelled by warming temperatures. These processes include enhanced basal sliding, inefficient subglacial drainage networks, and a warming of ocean waters in contact with the glacier terminus. Understanding the impact of meltwater on tidewater glacier dynamics, both subglacially and proglacially, is a key component in predicting glacier health and future sea level rise. However, the spatial and temporal magnitude of this meltwater impact is poorly understood. The goals of this dissertation are to identify how meltwater travels subglacially through a tidewater glacier system, establish a method to monitor tidewater glacier discharge remotely, and calculate the impact of subglacial discharge on terminus stability..;The inaccessibility of subglacial and terminus environments prohibits direct hydrological observations. We use combinations of remote sensing, reanalysis models, and in situ fjord data to accomplish these research goals by measuring indicators of subglacial meltwater discharge and fjord circulation (sediment plumes exiting the terminus and the movement of small icebergs in the fjord). By monitoring the timing and duration of plumes exiting a fast-flowing Greenland tidewater glacier, we found short-term variability in meltwater discharge, persistent subglacial pathways, and evidence of over-winter subglacial storage. Using glaciers in Svalbard, we established a new method to determine sediment concentration from Landsat--8 spectral reflectance, and used this sediment concentration to quantify relative seasonal meltwater discharge at tidewater glaciers. Finally, we used the movement of icebergs and ocean temperatures to establish a terminus submarine melt rate for along-terminus fjord circulation, and use this to isolate calving due solely to subglacial meltwater discharge.;The results of this dissertation help answer larger questions concerning the controls of water flow under a glacier and how that flow, and fjord circulation, influence glacier stability. Ultimately these results will inform coupled ice-ocean-climate models to predict glacier melt and sea level rise. |
