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The largest and most rapidly changing glaciers on Earth flow into the ocean. Ice loss from these glaciers will be the largest contributor to sea level rise in coming centuries and is also the least certain component of the sea level budget. These uncertainties are driven in large part by the poor understanding of two processes by which tidewater glaciers and ice sheets lose ice at their termini: submarine melting by warm ocean water and mechanical iceberg calving.
The fronts of tidewater glaciers are among the most active and inaccessible geological environments. These challenges have limited the long duration, high resolution calving and melt measurements that yield insight. Using seismology and oceanography, I identify the magnitudes and variability of submarine melt and iceberg calving at Yahtse Glacier, a major tidewater glacier in southern Alaska. I find that the submarine portion of the glacier terminus melts at over 10 m/d during much of the year. In addition, cavitation of icebergs beneath the sea surface can generate seismometer-recorded "icequakes," revealing that calving varies seasonally and in response to ocean tides. Seismic tremor also offers the first ever view of subglacial discharge from a tidewater glacier. Discharge increases during late summer, which promotes submarine melt. Together, these multidiscipline observations improve our understanding of the geophysical processes responsible for rapid ice loss across the cryosphere.