Lake water balance near Kangerlussuaq, Greenland and their potential response to future climate change

Glacial lakes are an important component of the Arctic landscape. These lakes affect the local water cycles, ecosystem functioning, and, if reaching a substantial surface area, the surface albedo and energy balance. Understanding the current water balance of lakes is thus important for predicting the response of the Arctic to future climate change. Lake water balance, specifically evaporation, was studied using both lake surface area and isotopic compositions of lake water. Direct observations were made of the surface area, bathymetry, and water volume of selected lakes. Remote sensing methods were also used to measure the lake surface area and water depth. The precipitation data from the Kangerlussuaq's weather station is used as the input of water flux into lakes. Over 40 precipitation- and glacier-fed lakes near Kangerlussuaq, Greenland were sampled for water isotopic measurements. Local river water and glacial melt were also sampled and analyzed. Our preliminary data show that glacial melt, glacial-fed lakes and river water define the local meteoric water line (LMWL) with a slope of 8.62. The precipitation-fed lakes define an evaporation line with a slope of 4.40 that intercepts the LMWL. The isotopic compositions at the intersection are used as the isotopic ratios of the input precipitation. The computation of the isotopic compositions of the evaporation flux requires the isotopic compositions of atmospheric water vapor, which we obtained by measurements over selected lakes using a Los Gatos Water Vapor Isotope Analyzer. Three mass balance equations, one for water and two for isotopic tracers (oxygen-18 and deuterium), are used to quantify the water balance of precipitation-fed lakes and to constrain lake surface evaporation and land evapotranspiration across the surrounding catchment area. In this model, the steady state lake surface area and isotopic compositions of lake water is a function of only the input and output water and isotopic fluxes. Using multiple lakes, we are able to constrain the evaporation rate across the landscape. With fluxes obtained from the model of the hydrological cycle, we can then predict future changes in lake surface areas by incorporating the projections of temperature and precipitation from the 2007 IPCC assessment. It has been observed that evaporation is the dominant process of the hydrologic cycle in such an arid polar continental climate, so it is expected that water volumes are likely to decrease in the future, causing some lakes even to dry up, although this may be complicated by the response of permafrost to climate change. Climate change and the resulting water volume decrease of lakes will impact the future water balance and this, in turn, will affect the chemistry of these lakes.