| Summary: | Subglacial discharge influences glacier basal motion and erodes and redeposits sediment. At tidewater glacier termini, discharge drives submarine terminus melting, affects fjord circulation, and is a central component of proglacial marine ecosystems. Subglacial discharge influences glacier basal motion and erodes and redeposits sediment. At tidewater glacier termini, discharge drives submarine terminus melting, affects fjord circulation, and is a central component of proglacial marine ecosystems. However, our present inability to track subglacial discharge and its variability significantly hinders our understanding of these processes. Here we report observations of hourly to seasonal variations in 1.5–10 Hz seismic tremor that strongly correlate with subglacial discharge but not with basal motion, weather, or discrete icequakes. Our data demonstrate that vigorous discharge occurs from tidewater glaciers during summer, in spite of fast basal motion that could limit the formation of subglacial conduits, and then abates during winter. Furthermore, tremor observations and a melt model demonstrate that drainage efficiency of tidewater glaciers evolves seasonally. Glaciohydraulic tremor provides a means by which to quantify subglacial discharge variations and offers a promising window into otherwise obscured glacierized environments. We thank the U.S. National Science Foundation for supporting data collection at Yahtse Glacier through grant EAR-0810313. T.C.B. was substantially supported by a postdoctoral fellowship from the University of Texas Institute for Geophysics. J.M.A. was supported by Alaska NASA EPSCoR Program (NNX13AB28A). S.O. was supported by the U.S. Geological Survey Climate and Land Use Change Mission and the U.S. Department of Interior Alaska Climate Science Center. Seismic instrumentationwas provided by the PASSCAL polar program of the Incorporated Research Institutions for Seismology (IRIS). Jamie Bradshaw and Marci Beitch assisted in the Mendenhall Glacier data collection effort. Two anonymous ...
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