Dynamic subglacial lakes and West Antarctic ice streams

In November 2007 we initiated field investigations on Mercer and Whillans ice streams of several subglacial lakes recently discovered by analysis of ICESat laser altimetry data. The primary objective of this project is to constrain the temporal dynamics of these lakes and their impact on ice stream flow variability. During the first of three field seasons, we installed 10 continuously recording GPS stations, including one with near real- time satellite data uplink. The stations are located over two medium-size subglacial lakes ('Lake Mercer' and 'Lake Whillans' of Fricker et al., 2007), two small subglacial lakes ('Lake 7' and 'Lake 14' of Fricker et al., 2007) and in several topographic lows, which may correspond to subglacial drainage conduits. In addition, we collected nearly 100 km of ice-penetrating radar data. The latter suggest that lakes Mercer and Whillans still contain no less than 8-9 meters of water, even after recent drainage events detected by ICESat. Active seismic surveys are planned in 2008-09 to establish the depth of these subglacial lake basins. Initial GPS results from Lake Mercer show that the lake surface subsided through the beginning of 2008 when it started to lift up at a rate of ~1cm day. This is consistent with the interpretation from the ICESat repeat-track measurements that the lake activity switched from draining to filling between November 2007 and March 2008, and constrains the timing of the switch much more accurately than is possible from the 4-6 month temporal sampling of ICESat. Improved modeling of hydropotentials indicates that the two major subglacial lakes instrumented by us (Lake Mercer and Lake Whillans) are located in separate subglacial watersheds. This may help explain the observed differences in their temporal behavior.