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This article is part of the Fall 2014 issue of the Earth Science Matters Newsletter.
During the summer in the northeast Pacific Ocean, the Alaska Coastal Current sweeps water with temperatures in excess of 12°C (~54°F) past the mouths of glaciated fjords and bays along the northwestern coast of North America. These warm waters contribute to net ice loss from Alaskan tidewater glaciers, however the details of this interaction remain uncertain. Understanding ice discharge from marine-terminating glaciers such as these is important because it is the primary mechanism responsible for sea level rise.
A team of NSF researchers including USGS CLU R&D scientists combined glaciological and oceanographic measurements to demonstrate that a large fraction of the rapid mass loss from Alaska’s tidewater glaciers is a result of submarine melt, that is, by ice melting below the sea surface. This important process, now on the edge of scientific discovery, has for decades been obscured by logistical challenges in making measurements. Their results support the idea that tidewater glaciers are strongly sensitive to changes in ocean temperature (i.e. two-way communication exists between glaciers and the oceans; each system is capable of triggering large scale changes in the other). The research took place at Alaska’s Yahtse Glacier in Icy Bay, one of the most remote sections of the Gulf of Alaska coastline.
The team used passive seismology to measure iceberg calving, GPS and time-lapse photography to measure ice speeds, and oceanographic measurements of water column properties such as temperature and depth. The data showed that freshwater subglacial meltwater (which is less dense than seawater) provides the ‘engine’ by which warm ocean water is brought to the glacier terminus where it can melt ice rapidly during the late summer and fall.
This research provides much needed understanding of marine-glacier instability and how these processes influence sea level rise. Additionally, the work will help to improve the accuracy and validity of models designed to predict future sea level change.
The article "Does calving matter? Evidence for significant submarine melt," was published in Earth and Planetary Science Letters and can be found at: https://pubs.er.usgs.gov/publication/70048144