Energy and water mass balance of Lake Untersee and its perennial ice cover, East Antarctica

Abstract

Lake Untersee is one of the largest perennially ice-covered lakes in Dronning Maud Land. We investigated the energy and water mass balance of Lake Untersee to understand its state of equilibrium. The thickness of the ice cover is strongly correlated with sublimation rates; variations in sublimation rates across the ice cover are largely determined by wind-driven turbulent heat fluxes and the number of snow-covered days. Lake extent and water level have remained stable for the past 20 years, indicating that the water mass balance is in equilibrium. The lake is damned by the Anuchin Glacier and mass balance calculation suggest that subaqueous melting of terminus ice contributes 40–45% of the annual water budget; since there is no evidence of streams flowing into the lake, the lake must be connected to a groundwater system that contributes 55–60% in order to maintain the lake budget in balance. The groundwater likely flows at a rate of ~8.8 × 10−2 m3 s−1, a reasonable estimate given the range of subglacial water flux in the region. The fate of its well-sealed ice cover is likely tied to changes in wind regime, whereas changes in water budget are more closely linked to the response of surrounding glaciers to climate change.

Sources of solutes and carbon cycling in perennially ice-covered Lake Untersee, Antarctica

“…The hydrological conditions of Lake Untersee play a key role on determining the major solute chemistry of the oxic water column. The closed-basin lake loses water only by sublimation of its ice cover and is recharged by subaqueous melting of glacial ice and subglacial meltwater with no summer moating 13 . The major solutes in Lake Untersee reflect a heritage of 12-10 ka of recharge from glacial meltwater and cryo-concentration of the ionic load in the water column.…”

“…To maintain hydrological balance the lake must be recharged by an equal inflow (i.e., Refs. 13,26 ). The lake is dammed at its northern sector by the Anuchin Glacier and mass balance calculations suggest that subaqueous melting of terminus ice contributes 40-45% of the annual water budget with subglacial meltwater contributing the remainder 13 .…”

Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

“…The thickness of the ice cover is set by the energy balance and by the mass balance of the ice cover, ice being removed by ablation at the surface and added to the bottom by freezing (McKay et al, 1985). Two different types of perennially ice-covered lakes are possible analogues for the lake that could have been present in ancient Gale crater: 1) lakes that are recharged entirely by inflowing melt streams, such as the lakes in the McMurdo Dry Valleys and 2) lakes that have significant recharge from subaqueous melting of abutting glaciers, such as Lake Untersee (Steel et al, 2015;Faucher et al, 2019). Sedimentary structures have been documented at the bottom of both types of lakes (Simmons et al, 1987;Squyres et al, 1991;Levitan et al, 2011 required in summer for meltwater to flow into the lake.…”

“…It is sealed by a ∼ 3m perennial ice cover and dammed by the Anuchin Glacier (Andersen et al, 2011;Wand et al, 1997;Steel et al, 2015;Faucher et al, 2019). The annual mean air temperature is -10.6C o The bottom of Lake Untersee is dominated by clay-sized sediment (although larger grains have been documented) and the mud in the lake is primarily derived from the abutting glacier (Steel et al, 2015;Faucher et al, 2019). At Lake Untersee, solar radiation penetrates the ice cover and melts the glacier's wall underneath the lake's surface, recharging the lake in meltwater.…”

“…Perennially ice-covered lakes also allow for stratification in water temperature and chemistry as ice covers prevent wind-driven turbulence within the lakes (Obryk et al, 2016;Townsend et al, 2009;Priscu et al, 1999). Lake Untersee is damned by a glacier so cooling of the water near the glacial wall induces a buoyancy-driven circulation that mixes the lake where the glacier reaches (Steel et al, 2015;Faucher et al, 2019). However, part of the lake is shielded from these currents and remains stratified (Bevington et al, 2018).…”