Water tracks intensify surface energy and mass exchange in the Antarctic McMurdo Dry Valleys
Abstract. We evaluated the hypotheses that water tracks alter the surface energy balance in the Antarctic McMurdo Dry Valleys and may serve as an indicator of landscape response to climate change in this dry, cold and ice-sheet-free environment. Water tracks are channel-shaped high moisture zones in the active layer of polar soils. The surface energy balance was measured for one water-track and two non-water-track reference locations in Taylor Valley during the Antarctic summer of 2012–2013. Turbulent atmospheric fluxes of sensible heat and evaporation were observed using the eddy-covariance method in combination with flux footprint modeling, which was the first application of this state-of-the-art technique in the Dry Valleys. Soil heat fluxes were analyzed separately for thawed and frozen layers at all locations via computing the change of the heat storage in the thawed layer from measurements. The results showed that for both water track and reference locations over 50 % of the net radiation was transferred to sensible heat exchange, about 30 % to melting the seasonally thawed layer, and the remainder to evaporation. The net energy flux in the thawed layer was zero. For the water track location, evaporation was increased by a factor of 3.0 relative to the references, ground heat fluxes by 1.4, and net radiation by 1.1, while sensible heat fluxes were reduced down to 0.7. Entertaining a realistic scenario of climate change in Taylor Valley in which the land cover fraction of water tracks increases by 50 %, the total evaporation from lower Taylor Valley would increase by 4 % to 0.30 mm d−1. In summary, our findings show that water tracks have a strong impact on the surface energy balance in ice-sheet free Antarctic regions. Water tracks are hot spots of change and are likely to respond faster to climate change signals than the dominant dry glacial till in the McMurdo Dry Valleys. Their spatiotemporal dynamics may therefore serve as indicator of high-sensitivity for change in permafrost-dominated cold landscapes.