Freezing of Lakes - Freezing of Lakes and the Evolution of their Ice Cover - page 44

2.4.3 Lakes with Perennial Ice

There are two categories of lakes with perennial ice. In very cold climate it is possible that
at least some of the ice grown in winter survives over summer and becomes multi-year ice.
The second category, proglacial lakes, contains liquid water bodies at side, on top and
beneath glaciers or ice sheets and therefore these lakes are always in contact with land ice.
If not all ice melts in summer, the ice cover consists of first-year ice and multi-year ice.

Example in Nunavut there are such lakes (Veillette et al. 2010). Occurrence of multi-year
lake ice was observed in Colour Lake, Axel Heiberg Island, Nunavut (Adams et al. 1989)
but it is there a rare event. Another lake sometimes possessing multi-year ice is Teshekpuk
Lake in Alaska (Arp and Jones 2011). But to the author ' s knowledge, in the present

climate, the coldest place in the Northern Hemisphere contains only seasonally

ice-covered lakes. In summer, lake ice melts mainly due to the radiation balance, which
may account for up to 2

— Siberia —

3 cm day − 1 in ice thickness. Therefore, if the melting period is
more than 100 days long, the melt volume will overcome the winter

-

' s ice growth. For a

partial summer ice cover to survive, the conditions must be quite speci c, since lakes have

rather small dimensions. It may take place if a lake has bays sheltered from direct solar
radiation etc. The partial ice cover state is something delicate between fully ice-covered
state and seasonal ice cover (Fig. 2.16 ).
Perennially fully ice-covered lakes are found in very cold climate conditions, when the
ice cover is snow-free and consists of clear ice, e.g., in the McMurdo Dry Valleys in
Antarctica (Priscu 1998). Then the surface heat balance can be predominantly negative.
Solar radiation heats the water body underneath, but the ice cover survives over summer.
Due to the low thermal conductivity of ice, the absorbed heat does not escape easily, and
accumulation of heat results in internal warming. This is similar to the so-called cool skin
phenomenon in lakes and seas during calm and clear summer days. In the case of ice
cover, the situation can be persistent, that leads to perennially ice-covered lakes. The ice
cover in these lakes has been observed to be several meters thick, in Lake Vida the ice
cover has been estimated as 20 m thick (Bar-Cohen et al. 2004).
There are three types of proglacial lakes connected to glaciers and ice sheets (e.g.,
Menzies 1995). Epiglacial lakes are found on the bare ground close to the boundary of the
land ice mass (Kaup 1994); subglacial lakes are very old water bodies at the base of ice
sheet (e.g., Siegert et al. 2001); and supraglacial lakes form in blue ice regions in the surface
layer in summer (Winther et al. 1996; Bajracharya and Mool 2009; Lepp

ranta et al. 2013).
Epiglacial lakes are as normal cold region lakes with a soil or rock bottom, fed mainly by
glacial melt water in

ä

ow. They are an important habitat of life in the polar world. Normally
these lakes have seasonal ice cover but blocks of glacial ice may be present.
Subglacial lakes are one of the most exciting geographical

fl

findings of the 20th century.

The first evidence of their existence was from Soviet radio-echo soundings in the 1960s

(see Priscu and Foreman 2009). Subglacial lakes are not yet well known but they form
very speci

c physical and microbiological systems at the bottom of the Antarctic ice
sheet. The water temperature is at the melting point corresponding to the ambient pressure,