Subglacial Hydrology


Overview

Hydrology is the study of liquid water’s properties, especially its movement in relation to land. For much of history, scientists believed that Antarctica contained to no liquid water; however during the Soviet Antarctic expeditions of 1959 to 1964 the Russian scientist Andrey Kapitsa along with others used seismic sounding (measuring how seismic waves pass through different materials) to discover a large body of water below the Antarctic ice sheet, later named Lake Vostok. Since then, 378 other subglacial lakes have been found in Antarctica through the use of aerial surveys and various remote sensing technologies.

These subglacial lakes are some of the least explored natural features on earth, and we are only beginning to understand the web of relationships between water, ice, and earth in the subglacial biome. Through using a variety of techniques, the SALSA project will to build off the foundational research provided by the WISSARD project in order better understand the dynamics of this hydrological system.

Observing Lake Activity

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Scientists checking on WISSARD’s permanent GPS station

From observing fluctuations in surface ice elevation using data from NASA’s Ice, Cloud, and Land Elevation Satellite laser altimeter, the European Space Agency’s radar altimeter, and WISSARD’s situ GPS station, we now understand that subglacial water intermittently fills and drains through a vast network of subglacial lakes. For some lake systems, we have been able to construct a full decade of lake activity, revealing internal variability on timescales ranging from days to years. The timescales on which variability occurs shows that long-time series observations are crucial to understand these systems.

Through installing permanent GPS stations, SALSA will refine methods for observing dynamic activity on short time scales and extend the time series of lake activity to 16 years. This will provide both background information for future drill sites and provide inputs for improved physical and chemical water modeling.

Stability of the Hydrologic System

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Water Sample from Lake Whillans

Many of the lakes along the Sipple Coast appear to form in wells that are controlled by depressions on the ice surface, as opposed to depressions on the earth’s topography. Therefore, as thicker sections of glaciers move over the continent, the water below must move into areas with less overlying ice. As the Whillans Ice Stream slows, it is possible that the ice surface thickness may be perturbed enough to change the hydrological system.

The timescales on which these changes occur is currently unknown, yet they are crucial to understanding the direction and fate of carbon, nutrients, and gasses in the system. In order to better understand the sensitivity of water flow paths below the Whillans and Mercer ice streams, SALSA will develop high resolution, time evolving maps along with annual digital elevation models of the lower Whillans/Mercer area.

Observing Ice-Lake Dynamics

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WISSARD Permanent GPS Station

During WISSARD, we found that a cascading flood event from Subglacial Lake Mercer interrupted the stick-slip motion of overlying ice. This showed that changes in the subglacial water system fundamentally alter the dynamics of ice flow in a manner that is rapidly evolving, immediate, and complex. We contend that long-term, continuous observations are critical to understanding the spacial and temporal scales on which subglacial hydrologic process influence the larger ice sheet system.

In order to better understand this interaction, we will use two permanent continuous GPS stations to record the activity of Subglacial Lake Mercer in fine detail. These long term GPS records will be supplemented by summer only GPS stations and the collection of kenematic GPS data in order to closely examine important surfaces such as the shoreline of subglacial lakes.

Modeling Subglacial Water Systems

Results from regional-scale modeling show that water volume change in subglacial lakes is accommodated primarily through channels eroding into subglacial sediment with melting of the overlying ice playing a secondary role. The carving of sediment channels has profound implications for aqueous biochemistry where the reworking of sediments alters the availability of nutrients and limits the availability of oxygen.

Through this understanding of biogeochemical dynamics, we can infer new constraints on the evolution of subglacial hydrology. In order to form a more complete model of subglacial hydrology, SALSA will compare our current model of lake drainage against the biogeochemical data collected from Subglacial Lake Mercer. This interdisciplinary approach to subglacial water modeling is the first of kind because until WISSARD, there were no direct observations of subglacial biogeochemistry to compare against.