Baikal is a cold lake. Only in May is it freed of ice.
Some years, in the north of the lake, the ice even remains in parts till June, and
sometimes blocks of ice drift in these areas as late as July.
The high heat capacity of the water and its great volume means that, immediately after
the clearance of ice in May and June, Baikal begins to build up heat from the sun's
radiation but the temperature of the water does not rise, and the lake remains
relatively cold. A surface temperature of +3 +4°C is maintained for a long time.
Only in the shallows and in bays does it rise to +10 +12°C. The surface waters begin to warm up in July and especially in August up to +14 +16°C.
A water temperature of from +16 to +18°C can be found at this time along the shores of
the southernmost end of the lake, near the mouth of the Selenga, in the Maloye Morye,
the Barguzin and Chivirkuysky bays, and along the sandy beaches at the mouth of the
Verkhnaya Angara. It is these places at Baikal that are best for tourism and recreation.
Low heat conductivity is typical of water which gives off heat very slowly.
Another peculiarity is the fact that it achieves its greatest density at +4°C.
This peculiarity is the main reason for the spring and summer warming of the
surface layer of water down to about 300 metres. Dense waters at +4°C
sink and mix with cold waters, gradually evening off the temperature in the surface
layer. In June the lake goes through a homothermic period (from the Greek 'homos'
- the same, equal), which is a levelling out of temperature in the top 300 metre
layer.
During the state of homothermy, the temperature of the water in the top 300
metre layer gradually rises. In June a period of temperature stratification occurs,
there arises a thin, well warmed surface layer separated from deep waters by a
temperature jump layer below which the water temperature gradually decreases.
In September Baikal's waters begin to cool and in November they again go
through a state of homothermy, the autumn one.
So the top 300 metre layer has two characteristic states, summer and winter. If
in summer the water temperature gradually decreases with depth, in winter, on the
contrary, it increases, from zero (and below) at the surface, immediately under the
ice, to a level of about +3.5 +3.8°C at a depth of 200 - 250 metres.
The top 250 - 300 metre layer of water with its temperature fluctuations is the
habitat of the vast majority of animal and plant populations of the lake.
Below the active layer is a body of water that has a small role to play in
temperature exchange with the atmosphere. This is a body of darkness, where no
sunlight penetrates. It is characterized by a relatively even temperature, which
goes down to +3.1 +3.4°C towards the bottom. Nevertheless, the influence of climate
fluctuations reaches even here, causing small, but nonetheless noticeable changes
of temperature within a year and from year to year.
As a result of the low heat conductivity of water, at a depth of one and a half
kilometres the mass of water maintains a low temperature. Adjacent to Baikal, at
the same depth, rocks, with a higher heat conductivity than water, have a
temperature of +50°C.
The cold of Baikal's watery belly has a significant influence on the
temperature of the rocky bed of the lake. In those places where the bed is frozen,
the water helps to maintain the minus temperatures; in other places where warm
streams or hot springs rise from the depths, Baikal's water neutralizes this
warmth. The warmth rising from the depths of the earth raises the temperature of
the bottom layers by no more than one tenth of a degree.
In general, it is thought that Baikal's water mass has a cooling effect on its
rocky bed. Back in the 1930s the hydrologist N.N.Korytoikova calculated the
temperature of the rocks beneath Baikal and found it to be lower than that at the
same depth but at some distance from the lake. In principle, these calculations
have been confirmed by present day investigators.
The temperature regime of the bottom layers in Baikal is disturbed by the
escape of deep thermal waters which mix with the relatively cold waters of the
lake. However, there is no significant rise in the temperature here because of the
mixing of these waters, as a result of which the warm input is dispersed in the
body of water. Thermal water vents have been registered during investigations
into warm deep water streams. Such a study has been carried out over many years
by a researcher into Baikal's depths, the Irkutsk scientist V.A.Golubev. He studies
warm streams with the help of temperature sensors let down from boats into the
silts of the lake and into the deepest bottom layers of water. Golubev has found
that deep thermal waters rise along definite zones, most probably along faults and
cracks in the rocks.
A centre for deep thermal waters under the belly of Baikal was first
discovered in 1976 in Frolikha bay (North Baikal). Later, underwater springs
were found at the outlet of the valleys of the rivers Bireya, Tompuda, Shegnanda,
and Bol'shaya Rechka. Small increases in temperature at the very bottom have
been registered here by direct measurements: from 0.02 to 0.15°C.
Thermal water vents have been found at depths of from 220 to 420 metres. It is
estimated that they cover an area of from 1 to 3 square kilometres. They are
spatially limited to underwater canyons.
It should be added that deep thermal water vents occur along the shores of
North Baikal, on the shore itself, which are linked with faults in the earth's crust.
These include the Kotelnikovsky, Khakusy, Davsha and other springs.
Deep thermal water vents have also been discovered under water along the
western shore of North Baikal in the Kukuisky canyon and at the Posol'sky
sandbank, near the mouth of the Selenga.
The temperature of the thermal waters rising from the floor of Baikal can be as
much as +50°C, according to calculations, but the volume of these
underwater springs is usually small. |
Temperature