Seismic Tremor Reveals Subglacial Discharge at Tidewater Glaciers

Wednesday, 17 December 2014: 11:20 AM
Timothy C Bartholomaus1, Christopher F Larsen2, Shad O'Neel3, Michael Edwin West4, Jason M Amundson5, Jacob I Walter1, Ginny A Catania1, Leigh A Stearns6, Ryan T Walker7, Dave Sutherland8, Emily Shroyer9 and Jonathan D Nash9, (1)University of Texas, Institute for Geophysics, Austin, TX, United States, (2)University of Alaska Fairbanks, Fairbanks, AK, United States, (3)USGS Alaska Science Center, Anchorage, AK, United States, (4)University of Alaska Fairbanks, Anchorage, AK, United States, (5)University of Alaska Southeast, Juneau, AK, United States, (6)University of Kansas, Department of Geology, Lawrence, KS, United States, (7)University of Maryland, Greenbelt, MD, United States, (8)University of Oregon, Eugene, OR, United States, (9)Oregon State Univ, Corvallis, OR, United States
Subglacial discharge from the termini of tidewater glaciers drives submarine terminus melting, influences fjord circulation, erodes and redeposits subglacial sediment, and is a central component of proglacial marine ecosystems. The timing and variability of subglacial discharge can also exert a strong influence on the upstream flow of tidewater glaciers through hydrology-mediated changes in basal motion. However, a lack of observations of subglacial discharge at the ice-ocean interface hinders progress in understanding these processes and contributes to some of the largest uncertainties in sea level rise projections. Here we demonstrate that passive seismic observations collected adjacent to glaciers can meet this observational need. At tidewater and lake-terminating glaciers in Alaska and Greenland, we observe hourly to seasonal variations in low-amplitude, background seismic noise, termed glacio-hydraulic tremor. Variations in tremor amplitude correlate with discharge during the drainage of a glacially-dammed lake and reveal increases in discharge efficiency over the course of the melt season. Recordings of glacio-hydraulic tremor across a range of settings suggest widespread utility for our method. Reliable prediction of future sea level rise requires observations of subglacial discharge that elicit physical insight and can validate models. Our findings provide a platform for new understanding of ice-ocean interactions and related oceanographic, geologic, and ecological disciplines.