Proglacial Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 197

regions of eastern Antarctica (Siegert et al. 2001). Recently subglacial lakes have been
found also in Greenland (Palmer et al. 2013) and European Alps (Vincent et al. 2012).
There is evidence that subglacial Lake McGregor existed under the Laurentide ice sheet in
North America in the last glacial maximum (Munro-Stasiuk 2003).
The earliest evidence of Antarctic subglacial lakes was from Russian aircraft pilots

fl flying missions over the Antarctic continent. The presence of the lakes was subsequently

veri

echo sounding during the 1960s and
1970s (Masolov et al. 2006). We now know that more than 150 lakes exist beneath the
Antarctic ice sheet, many of which may be connected by large subglacial rivers. The
largest of them is Lake Vostok (Zotikov 2006). Approximately 81 % of the detected lakes
lie at elevations less than 200 m above the mean sea level, while the majority of the
remaining lakes are

ed by seismic investigations and airborne radio

-

at higher elevations. Sixty-six percent of the lakes lie within
50 km of a local ice divide. The high density of lakes in the Dome-C region implies that
they may be hydrologically connected within the same watershed and would be an
important system to study from the standpoint of subglacial hydrology and biological and
geochemical diversity.

' perched '

6.4.1 Formation and Diversity

Subglacial lake environments rest at the intersection of continental ice sheets and the
underlying lithosphere. This unique location sets the stage for generating a spectrum of
subglacial environments re ective of the complex interplay of ice sheets and the litho-

sphere. The association of subglacial lakes with local ice divides leads to a fundamental
question concerning the evolution of the lake environments. Is the location determined by
the ice sheet or by characteristics of the lithosphere (e.g., basal morphology, geothermal
fl

fl

flux, sub-ice aquifers)? With the exception of central West Antarctica, where only few
lakes exist, we know little about either the lithospheric character along these catchment
boundaries or the history of their migration, given by layering within the ice sheet.
There are two factors that lead to the formation of subglacial lakes: the presence of
geothermal heat ux (Q g ) at the base of the ice sheet and the good insulation capacity of

the ice sheet. At the lake surface, the phase equilibrium and the continuity of the heat

fl

fl ow

require that

TH ðÞ ¼ ; t T f ð p ; S Þ ð 6 : 17a Þ

z¼H þ

q w L dH k i @

T

dt ¼

Q g ð 6 : 17b Þ

@ z

where H is the depth of the lake surface from the top of the ice sheet. Considering a long-
term balance, we can assume a linear temperature gradient across the ice sheet. At the
steady state, H ¼ constant and the geothermal heat fl flux is fully conducted through the ice