Proglacial Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 184

Epishelf lakes are formed in marine embayments or fjords, dammed by advancing
glaciers and ice shelves. The marine water is replaced by fresh melt water from glaciers and
snow. In some cases a hydraulic connection to the sea persists under the ice shelf or glacier,
sometimes more than 100 m below sea level. Then the epishelf lake becomes meromictic.
Many of the lakes at lower altitudes in ice-free areas are below the Holocene marine
limit (below 40 m in the Antarctic Peninsula, below 8 m in the Larsemann Hills) and have
formed in depressions emerging from the sea as a result of postglacial isostatic rebound.
Where the lakes have no surface out ow they are referred to as closed (or endorheic)

lakes. Some of these closed lakes have subsequently experienced an excess of evaporation
over precipitation and have gradually become saline. Examples of these are found in the
McMurdo Dry Valleys. Some saline lakes become strati

fl

ed for part of the year (mono-

mictic) and others are permanently strati ed (meromictic). Lakes that have out fl ow

streams are classi ed as open lakes; these typically contain fresh water and do not

accumulate salts to the same degree as closed lakes do. Both types of lake are common in
Antarctic oases and maritime Antarctic islands.
When the main water source is glacial meltwater, the heat budget provides a limitation
to the discharge. The heat provided for melt is Q n A n T n , where Q n is the mean net heat

ux,
A n is the ablation area, and T n is the length of the ablation period. The volume of lake
water becomes

fl

Q n A n T n
q

V ¼ ð 6 : 2 Þ

L f

ow and can be considered as the
scale of the lakes with 1-year renewal time. In the cold season, the ice cover of epiglacial
lakes grows due to heat loss from the lake to the atmosphere as presented in Chap. 4 . The
water body becomes perennial if the depth is more than the thickness of ice, i.e.

This is the maximum volume for the annual water in fl

V
A [

H ¼ h max ð 6 : 3 Þ

where A is the lake area and h max is the maximum annual ice thickness. In case the ice
cover is seasonal, h max *

2 m serves as a good estimate for very cold climate conditions
(see Sect. 4.3 ). There are polar lakes with a perennial ice cover, e.g. in McMurdo Dry
Valleys in Antarctica. There Lake Vida has the thickest ice cover, about 20 m (Doran et al.
2004; Mosier et al. 2007). To achieve such large thickness is possible when the summer
melting remains small (see Eq. 4.56 ).

100 W m − 2 , A n * 100 km 2 Example 6.2 . For Q n * and T n * 100 days, we have

0.28 km 3 . For h max > 10 m, the water body is perennial, and the horizontal scale is V

*

p

V = h max < 170 m. But for h max < 1 m, the water body is seasonal, and the horizontal

p

V scale is = h max >530m.