Spatial and Temporal Lags in Meltwater Propagation Through the Greenland Ice Sheet Drainage System
Channel: moulinology
Date: 2021-12-11

Speaker: Jessica Mejia

Co-authors: Jason Gulley, Celia Trunz, Matthew Covington, Timothy Bartholomaus, Charles Breithaupt, Ronald Knoll, Victoria Siegel, Surui Xie,  Timothy Dixon


Session: Advances in Glacier and Ice Sheet Hydrology II
Tuesday, 14 December 2021 
14:07 - 14:12
Convention Center - Room 211-213

Link to presentation on the AGU Fall Meeting website: https://agu.confex.com/agu/fm21/meetingapp.cgi/Paper/962963


Abstract
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Recent observations from the Greenland Ice Sheet's (GrIS) ablation indicate peak sliding speed occurs later in the day at upglacier sites relative to sites closer to the margin (Hoffman et al., 2011). These observations reveal spatial and temporal differences in hydrodynamic coupling that are not currently captured by ice sheet models. Here, we test whether differences in temporal lags between meltwater production and delivery to moulins explain differences in timing of peak sliding speeds in the GrIS ablation area. We established two field camps at different elevations—a lower elevation field camp, Low Camp (700 m.a.s.l), and a higher elevation camp, High Camp (900–1,000 m.a.s.l.)—on Sermeq Avannarleq, western GrIS. We constrain the timing of peak melt, meltwater delivery to moulins, moulin water level, and ice sliding speeds at each site during the 2017 melt season, and incorporate measurements of glaciohydraulic tremor during 2018. We use these observations to investigate how differences in the physical characteristics of supraglacial drainage basins control lags between peak meltwater production and delivery to moulins. Increased temporal lags between peak meltwater production and delivery caused peak moulin water level to occur ~2 hours later at our upglacier site relative to our downglacier sites. However, this delay did not entirely account for the timing of peak sliding speed which lagged peak moulin water level by 2.8±2.0 hours at High Camp. These observations indicate there are non-local controls on sliding at higher elevations on the GrIS, that are not observed at lower elevations. On seasonal timescales, we observed decreasing lags between meltwater production and delivery to moulins that corresponded to the retreating snowpack throughout the melt season. Importantly, our work reveals the timing of peak subglacial pressures varies with elevation and distance from the margin and that this spatial variability has important implications for the coupling between hydrology and sliding.