SUB-ICE PROCESSES IN LAKE HOARE, ANTARCTICA; PART 1. CONTROLS ON STREAM SEDIMENT DEPOSITION

The McMurdo Dry Valleys (MDV) in Antarctica are widely considered to be the most Mars-like environment on Earth. Perennially ice covered lakes in the MDV provide insight into physical, chemical, and biological process that potentially occurred in Mars lakes. Lake Hoare occupies a 4-km-long, closed-basin fed by a glacial meltwater stream called Andersen Creek, runoff from the Canada Glacier, and overflow from an adjacent pond. Shore ice around the perimeter of Lake Hoare is thinner and more transparent than the 4-m-thick perennial ice in the interior. Unlike other MDV lakes, the surface of the shore ice in Lake Hoare typically remains frozen throughout the summer and insulates liquid water at depth. Similar shore ice characteristics may have occurred in Mars lakes. This study investigated the fate of Andersen Creek water in Lake Hoare in order to indicate where stream sediments may have been deposited in Mars lakes. Andersen Creek water entering Lake Hoare will either: (1) disperse on top of shore ice as overflow; (2) flow West under the shore ice in a counter-clockwise direction as a result of geostrophic forcing; (3) flow South under the perennial lake ice as interflow; or (4) follow the bathymetric gradient as underflow. Between 28 November 2012 and 6 January 2013, hourly water temperatures were recorded at the Andersen Creek stream gage and beneath the shore ice near the stream inlet. On 17 December 2012, a LiCl tracer (Li⁺ 49 g/L, Cl^- 251 g/L) was injected into the Andersen Creek weir for 2 hours during a diurnal discharge event which peaked at 74 l/sec. Water samples were collected every 30 minutes for 4 hours from 5 stream sites and 15 boreholes drilled into the shore and perennial ice. Samples were analyzed for major cations and anions using ion chromatography. Tracer results showed that stream water moved West below the shore ice, consistent with geostrophic rotation (see http://dx.doi.org/10.6073/pasta/caabb61955022b653fa61a08383c3311). Water temperatures below the shore ice were consistent with stream water temperatures from roughly the start of stream flow on 6 December until the end of the study, suggesting stream water flowed below the shore ice during most of the summer. If Mars lakes behaved similarly, we would expect to find greater accumulations of stream sediments along lake shorelines compared to lake interiors.