Geochemical characterization of subglacial water from the West Greenland Ice Sheet

The residence time of water in the basal drainage system of the Greenland Ice Sheet is key to understanding ice-ocean-bedrock-climate interaction and ice flow mechanisms. Quantitative analysis of the geochemical and isotopic composition of water in the subglacial environment can be used as a direct indicator of water residence time, and may identify the sources of water as well as its route from surface to outlet. Water plays a first-order role in the modulation of basal sliding and is an important component of fast ice flow. Therefore, addressing questions of routing and residence time is important for understanding the relationship between the hydrologic system of the ice, sliding speed, and climate. During June 2010, eleven boreholes were drilled through the near-marginal ice of West Greenland to bedrock using a newly-redesigned hot-water drilling system. Basal water was collected from the holes using a gravity sampler and was characterized by its radon activity and geochemistry. The low activity of 222Rn in subglacial water and its ion chemistry, compared with surface meltwater, indicates that most water at the base of the ice is surface melt that has reached the bed. Furthermore, residence time in the subglacial system is short, suggesting that basal drainage near the margin of the Greenland Ice Sheet is efficient and well-channelized. Water samples from these ice-marginal boreholes and the results of the geochemical analyses are the first in a series of three sets of holes that will be drilled in a flow-line transect of the Greenland Ice Sheet. We will discuss expectations for the next two years of drilling operations and we will present new geochemical results in coming years.