This award supports a three-year study of the ongoing deceleration and stick-slip motion of Whillans Ice Stream (WIS), West Antarctica. Understanding the dynamic behavior of ice streams is essential for predicting the future of the West Antarctic Ice Sheet (WAIS). Despite being one of the best-studied ice streams in Antarctica, the surprising flow characteristics of WIS continue to demand interdisciplinary research. Recent estimates indicate that the WIS may stagnate within 50 years, resulting in a significant change to the mass balance of the Siple Coast sector of West Antarctica. The reasons for the ongoing stagnation are not well known, and are possibly linked (causally or coincidentally) to the stick-slip behavior. Our recent work on WIS stick-slip motion suggest that all slip events nucleate from a common location on the ice stream, suggesting that a relatively small (approximately 10 km in diameter) region of the exerts fundamental control over the flow of this large ice stream (100s of km long and 100 kilometers wide). We hypothesize that this is a region of increased bed strength and our measurements will address that hypothesis. We will deploy a series of GPS receivers and seismometers on the ice stream to accurately locate the nucleation region so that a comprehensive ground based geophysical survey can be conducted to determine the physical properties of bed at the nucleation point. The ground geophysical program will consist of reflection seismic and ice-penetrating radar studies that will better constrain the properties of both the hypothesized higher-friction nucleation zone and the surrounding regions. Slip events also generate seismic energy that can be recorded 100s of km away from the ice stream, thus, the GPS and seismometer deployment will also aid us in relating seismic waveforms directly with the rapid motion that occurs during slip events. The increased ability to relate rupture processes with seismic emissions will allow us to use archived seismic records to explore changes in the behavior of WIS during the later half of the 20th century. Broader impacts of this study include improved knowledge ice sheet dynamics, which remain a poorly constrained component of the climate system, thus, limiting our ability to predict the Earth's response to climate change. The scientific work includes the education of two graduate students and continued training of one post-doctoral scholar, thus helping to train the next generation of polar scientists. We will expose the broader public to polar science through interactions with the media and by take advantaging of programs to include K-12 educators in our field work.
Ice streams are giant rivers of ice that form the main conveyor of ice from the Antarctic Ice Sheet into the world’s oceans. Thus, a better understanding of ice stream flow is required to forecast how ice sheets respond to climate change. Melting at the underside of an ice stream, due to geothermal heat and frictional heat from ice sliding over its bed, results in a thin layer of water at the bottom of ice streams, allowing them to slide rapidly. However, if the water source beneath an ice stream becomes restricted, the ice-stream bed may become sticky, resulting in decreased flow speeds. This project focused on the Whillans Ice Stream, a large ice stream (300 km long up to 100 km wide) draining the interior of the West Antarctic Ice Sheet, where decreased flow speeds have been observed over the past several decades. This slow down potentially indicates that the supply of water at the ice-stream bed may have become restricted. To understand to current deceleration of the Whillans Ice Stream we conducted geophysical surveys during both the 2010/11 and 2011/12 Antarctic summers. The field team primarily consisted of undergraduate and graduate students. The experiments included the deployment of GPS receivers to monitor the ice stream motion as well as a seismic survey to measure how much water was at the base of the ice stream. The third image shows the seismic image of the ice-stream bed generated during this study. The strength of the echo can be used to determine the amount water present at the bottom of the ice stream. The results of our experiment have shown that unlike other fast flowing regions of the ice sheet, the bed beneath the Whillans Ice Stream is starved for water. Thus, we have confirmed that the decrease in flow speed of this ice stream is due decreased availability of water at the bed. The results of this work have improved our ability to both understand and monitor the changing behavior of Earth’s large ice sheets.
