Climatic controls on the summertime energy balance of a thermokarst lake in northern Alaska: Short-term, seasonal, and interannual variability

Abstract

Shallow, thermokarst lakes that develop atop permafrost are a prominent landscape feature on the Arctic Coastal Plain (ACP) of northern Alaska. The ACP is vulnerable to ongoing climate change and landscape modification, as thousands of thaw lakes and ponds are impacted by changes in temperature, precipitation, thawing permafrost, and human activity. Although summer in the Arctic is short, incoming solar radiation and lake evaporation are relatively high, and both factors play a significant role in the landscape water balance. Furthermore, lake evaporation is anticipated to increase as the ice-free season lengthens and water temperatures become warmer. To improve our understanding of these processes, we performed a multi-year energy balance analysis of a shallow, thermokarst lake near Barrow, Alaska. Timeseries of net radiation, Bowen ratio, and rates of heat storage in the water and sediments were used to calculate sensible and latent heat fluxes during the 2008-2010 ice-free periods. Results of the energy balance analysis show rapid lake warming immediately following ice-off (due to high insolation), followed by similar increases in sensible and latent heat flux. Lake evaporation averaged around 1.3 mm/day during the ice-free period, which is nearly twice the mean summertime precipitation rate of 0.7 mm/day for Barrow, Alaska. Daily evaporation rates ranged from zero to greater than 4 mm/day, while short-term and seasonal patterns varied significantly from one year to the next. Much of this variability was associated with changes in cloud cover, water temperature, relative humidity, and wind speed.