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Seasonal and Interannual Variability in the Hydrology and Geochemistry of an Outlet Glacier of the Greenland Ice Sheet

Benjamin Linhoff, Ph.D., 2016
Matthew Charette, Advisor

Distributed system drainage is a key component in stabilizing the Greenland Ice Sheet velocity on interannual time scales and controlling subglacial weathering. I conducted 180 days of fieldwork in the spring and summer at an outlet glacier in Greenland. I developed a method based on continuous 222Rn measurements in a proglacial river to determine the timing and magnitude of subglacial distributed system drainage. These results were compared with glacial velocity and modeled supraglacial meltwater runoff. Major spikes in 222Rn associated with distributed system drainage occurred after rapid inputs of supraglacial meltwater runoff and during the expansion of the subglacial channelized system. Hence, rapid increases in meltwater runoff that induce short-term glacial acceleration also increase drainage from the distributed system, a process that likely leads to slower winter glacial velocities. Sr, U, and Ra isotopes were used to investigate the impact of glacial hydrology on subglacial weathering. That trace carbonates within the silicate watershed controlled the 87Sr/86Sr ratio in the dissolved load. δ234U and (228Ra/226Ra) results demonstrated that while glaciation causes extensive physical weathering, subglacial hydrology causes significant chemical weathering. In summary, extensive, repeated cycles of rapid supraglacial meltwater runoff leads to increased distributed system drainage and mineral weathering.