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Ice regime. Subglacial currents

Air temperature. General trend of air temperature changes at Lake Baikal corresponded to the global temperature trend with its rise from the late 1910-s to the middle of the 20^th century, to the temperature decrease by the early 1970-s and its significant rise by the end of the 20^th century. The trend of annual temperature in the lake area (+1.2°C/100 years) was two times higher than the average Earth’s trend (+0.6°C/100 years). The rise of air temperature was recorded for all seasons of the year from 1986 to 2008 with the trend of +1.9, +1.5, +1.1 and +0.66°C/100 years in winter, spring, summer and autumn, respectively. Maximal trend (+2.1-2.2°C) was registered in December and January and minimal trend (+0.1-0.5°C) in August, September and October.  Statistical analysis showed both short-term (2-7 years) and long-term inter-annual (about 20 years) cycles with well-defined phases of increase and decrease of air temperature. The 20^th century had two complete cycles (1912-1936 and 1937-1969) and phases of two incomplete cycles – decrease from 1896 to 1911 and increase from 1970. The increase phase at the end of the century to the mid 1990-s was characterized by anomalously long duration (25 years) and rise of air temperature (by 2.1°C). Beginning from 1995, there was a tendency to annual temperature decrease, which may be regarded as the beginning of the temperature drop phase in the current inter-annual climate cycle.

Temperature of water surface. The temperature of water surface increased together with the rise of air temperature due to global warming. According to the observation data since 1941, the average temperature of water surface in Southern Baikal (the settlement of Listvennichnoye) decreased insignificantly in May-September from the 1950-s to the 1970-s, and then sharply increased by the mid 1990-s. The same temperature changes were recorded in other areas of the lake. The rate of its increase (0.64-0.60°C/10 years) was higher in the central and northern parts of Lake Baikal than in its southern part (0.25-0.35°C/10 years). The temperature of the warmer 1994-2005 decade exceeded the temperature of the cold 1964-1975 period by 0.9-1.5°C in the southern area and by 1.8-2°C in the central and northern regions of the lake. In some years of this period (e.g., several days in August of 2002), the increase of surface water temperature up to 18-20°C was recorded even in the deeper areas of the lake.

Ice regime. Beginning in the middle of the 20^th century, the warming caused “mitigation” of the ice regime at Lake Baikal [Verbolov et al., 1965; Magnusson et al., 2000]. Freezing of the lake started later, whereas ice breaking began earlier. In1868-2010, in Southern Baikal (the settlement of Listvennichnoye) the trend of freezing and ice breaking terms were 10 and 7 days per 100 years, respectively. The duration of ice free period prolonged, whilst the ice cover period shortened by 17 days. According to the 1950-2010 data, the maximal ice thickness decreased on average by 2.4 cm every 10 years. During the phase of significant warming (1970-1995,) the rate of ice process changes sharply increased: freezing started by 10 days later and ice breaking by 15 days earlier; the ice period shortened by 25 days, and the ice thickness decreased on average by 8.8 cm per 10 years. The observation data from shore stations and satellites showed that beginning from the mid 1990-s to the middle of 2010 there was a tendency towards early freezing, late break-up of ice and prolongation of ice period [Kouraev et al., 2007]. These changes are consistent with inter-annual climate periodicity associated with fluctuations of atmospheric circulation in the Northern Hemisphere.

The main meteorological factor, which causes fluctuations of freezing terms (D_fr) is the air temperature in November-December (T_a) affecting the rate of heat losses from the water surface. The correlation between these characteristics in Southern Baikal is described by equation D_fr=4.26Тa+75 (R²=0.57, p<0.001) for the period of 1896-2010, where D_fr is the number of days from December 1^st to the freezing date. Temperature conditions in spring also affect the date of ice breaking. However, the correlation between ice breaking dates and air temperature is not high [Livingston, 1999]. It is attributed to the effect of both thermal and dynamic (wind) factors on the break-up of ice [Kouraev et al., 2007; Shimaraev, 2008], as well as to the influence of ice thickness, which depends on air temperature in winter months.

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Temperature of  water  surface according to satellite data

Air temperature. General trend of air temperature changes at Lake Baikal corresponded to the global temperature trend with its rise from the late 1910-s to the middle of the 20^th century, to the temperature decrease by the early 1970-s and its significant rise by the end of the 20^th century. The trend of annual temperature in the lake area (+1.2°C/100 years) was two times higher than the average Earth’s trend (+0.6°C/100 years). The rise of air temperature was recorded for all seasons of the year from 1986 to 2008 with the trend of +1.9, +1.5, +1.1 and +0.66°C/100 years in winter, spring, summer and autumn, respectively. Maximal trend (+2.1-2.2°C) was registered in December and January and minimal trend (+0.1-0.5°C) in August, September and October.  Statistical analysis showed both short-term (2-7 years) and long-term inter-annual (about 20 years) cycles with well-defined phases of increase and decrease of air temperature. The 20^th century had two complete cycles (1912-1936 and 1937-1969) and phases of two incomplete cycles – decrease from 1896 to 1911 and increase from 1970. The increase phase at the end of the century to the mid 1990-s was characterized by anomalously long duration (25 years) and rise of air temperature (by 2.1°C). Beginning from 1995, there was a tendency to annual temperature decrease, which may be regarded as the beginning of the temperature drop phase in the current inter-annual climate cycle.

Temperature of water surface. The temperature of water surface increased together with the rise of air temperature due to global warming. According to the observation data since 1941, the average temperature of water surface in Southern Baikal (the settlement of Listvennichnoye) decreased insignificantly in May-September from the 1950-s to the 1970-s, and then sharply increased by the mid 1990-s. The same temperature changes were recorded in other areas of the lake. The rate of its increase (0.64-0.60°C/10 years) was higher in the central and northern parts of Lake Baikal than in its southern part (0.25-0.35°C/10 years). The temperature of the warmer 1994-2005 decade exceeded the temperature of the cold 1964-1975 period by 0.9-1.5°C in the southern area and by 1.8-2°C in the central and northern regions of the lake. In some years of this period (e.g., several days in August of 2002), the increase of surface water temperature up to 18-20°C was recorded even in the deeper areas of the lake.

Ice regime. Beginning in the middle of the 20^th century, the warming caused “mitigation” of the ice regime at Lake Baikal [Verbolov et al., 1965; Magnusson et al., 2000]. Freezing of the lake started later, whereas ice breaking began earlier. In1868-2010, in Southern Baikal (the settlement of Listvennichnoye) the trend of freezing and ice breaking terms were 10 and 7 days per 100 years, respectively. The duration of ice free period prolonged, whilst the ice cover period shortened by 17 days. According to the 1950-2010 data, the maximal ice thickness decreased on average by 2.4 cm every 10 years. During the phase of significant warming (1970-1995,) the rate of ice process changes sharply increased: freezing started by 10 days later and ice breaking by 15 days earlier; the ice period shortened by 25 days, and the ice thickness decreased on average by 8.8 cm per 10 years. The observation data from shore stations and satellites showed that beginning from the mid 1990-s to the middle of 2010 there was a tendency towards early freezing, late break-up of ice and prolongation of ice period [Kouraev et al., 2007]. These changes are consistent with inter-annual climate periodicity associated with fluctuations of atmospheric circulation in the Northern Hemisphere.

The main meteorological factor, which causes fluctuations of freezing terms (D_fr) is the air temperature in November-December (T_a) affecting the rate of heat losses from the water surface. The correlation between these characteristics in Southern Baikal is described by equation D_fr=4.26Тa+75 (R²=0.57, p<0.001) for the period of 1896-2010, where D_fr is the number of days from December 1^st to the freezing date. Temperature conditions in spring also affect the date of ice breaking. However, the correlation between ice breaking dates and air temperature is not high [Livingston, 1999]. It is attributed to the effect of both thermal and dynamic (wind) factors on the break-up of ice [Kouraev et al., 2007; Shimaraev, 2008], as well as to the influence of ice thickness, which depends on air temperature in winter months.

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Temperature of surface water layers

Air temperature. General trend of air temperature changes at Lake Baikal corresponded to the global temperature trend with its rise from the late 1910-s to the middle of the 20^th century, to the temperature decrease by the early 1970-s and its significant rise by the end of the 20^th century. The trend of annual temperature in the lake area (+1.2°C/100 years) was two times higher than the average Earth’s trend (+0.6°C/100 years). The rise of air temperature was recorded for all seasons of the year from 1986 to 2008 with the trend of +1.9, +1.5, +1.1 and +0.66°C/100 years in winter, spring, summer and autumn, respectively. Maximal trend (+2.1-2.2°C) was registered in December and January and minimal trend (+0.1-0.5°C) in August, September and October.  Statistical analysis showed both short-term (2-7 years) and long-term inter-annual (about 20 years) cycles with well-defined phases of increase and decrease of air temperature. The 20^th century had two complete cycles (1912-1936 and 1937-1969) and phases of two incomplete cycles – decrease from 1896 to 1911 and increase from 1970. The increase phase at the end of the century to the mid 1990-s was characterized by anomalously long duration (25 years) and rise of air temperature (by 2.1°C). Beginning from 1995, there was a tendency to annual temperature decrease, which may be regarded as the beginning of the temperature drop phase in the current inter-annual climate cycle.

Temperature of water surface. The temperature of water surface increased together with the rise of air temperature due to global warming. According to the observation data since 1941, the average temperature of water surface in Southern Baikal (the settlement of Listvennichnoye) decreased insignificantly in May-September from the 1950-s to the 1970-s, and then sharply increased by the mid 1990-s. The same temperature changes were recorded in other areas of the lake. The rate of its increase (0.64-0.60°C/10 years) was higher in the central and northern parts of Lake Baikal than in its southern part (0.25-0.35°C/10 years). The temperature of the warmer 1994-2005 decade exceeded the temperature of the cold 1964-1975 period by 0.9-1.5°C in the southern area and by 1.8-2°C in the central and northern regions of the lake. In some years of this period (e.g., several days in August of 2002), the increase of surface water temperature up to 18-20°C was recorded even in the deeper areas of the lake.

Ice regime. Beginning in the middle of the 20^th century, the warming caused “mitigation” of the ice regime at Lake Baikal [Verbolov et al., 1965; Magnusson et al., 2000]. Freezing of the lake started later, whereas ice breaking began earlier. In1868-2010, in Southern Baikal (the settlement of Listvennichnoye) the trend of freezing and ice breaking terms were 10 and 7 days per 100 years, respectively. The duration of ice free period prolonged, whilst the ice cover period shortened by 17 days. According to the 1950-2010 data, the maximal ice thickness decreased on average by 2.4 cm every 10 years. During the phase of significant warming (1970-1995,) the rate of ice process changes sharply increased: freezing started by 10 days later and ice breaking by 15 days earlier; the ice period shortened by 25 days, and the ice thickness decreased on average by 8.8 cm per 10 years. The observation data from shore stations and satellites showed that beginning from the mid 1990-s to the middle of 2010 there was a tendency towards early freezing, late break-up of ice and prolongation of ice period [Kouraev et al., 2007]. These changes are consistent with inter-annual climate periodicity associated with fluctuations of atmospheric circulation in the Northern Hemisphere.

The main meteorological factor, which causes fluctuations of freezing terms (D_fr) is the air temperature in November-December (T_a) affecting the rate of heat losses from the water surface. The correlation between these characteristics in Southern Baikal is described by equation D_fr=4.26Тa+75 (R²=0.57, p<0.001) for the period of 1896-2010, where D_fr is the number of days from December 1^st to the freezing date. Temperature conditions in spring also affect the date of ice breaking. However, the correlation between ice breaking dates and air temperature is not high [Livingston, 1999]. It is attributed to the effect of both thermal and dynamic (wind) factors on the break-up of ice [Kouraev et al., 2007; Shimaraev, 2008], as well as to the influence of ice thickness, which depends on air temperature in winter months.

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Radiation and thermal balance of water surface

Absorbed solar radiation is the main thermal source of the lake water column. It depends on incident solar radiation and the ratio of reflected radiation (albedo). Thus, it has a well-defined seasonal trend. Radiation balance of the Lake Baikal water surface is a sum of absorbed solar radiation and effective radiation of water surface. This balance is positive from April to September and negative from October to March. In general, radiation balance of the lake is positive throughout the year, changing from 1,900 MJ/m² in the Selenga river area to 700-800 MJ/m² in the northern part of the lake. Spatial distribution of radiation balance of the lake surface depends on cloud regime during warm period. Radiation balance varies insignificantly because of inconsiderable changes of the cloud cover. In cold period, the distribution of radiation balance is influenced not only by the cloud cover but also by the difference in the albedo of water and snow. Therefore, the radiation balance in Northern Baikal is much lower than that in Central and Southern Baikal. Radiation balance of the water surface is a determining element in the thermal regime of the lake. Because of high water heat capacity, constant time lag is recorded in the seasonal trend of temperature parameters in comparison with radiation characteristics. Therefore, maximal accumulated radiation and radiation balance are recorded at Lake Baikal in June and the highest air and water temperatures in August.

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Radiation and thermal balance of water surface

Absorbed solar radiation is the main thermal source of the lake water column. It depends on incident solar radiation and the ratio of reflected radiation (albedo). Thus, it has a well-defined seasonal trend. Radiation balance of the Lake Baikal water surface is a sum of absorbed solar radiation and effective radiation of water surface. This balance is positive from April to September and negative from October to March. In general, radiation balance of the lake is positive throughout the year, changing from 1,900 MJ/m² in the Selenga river area to 700-800 MJ/m² in the northern part of the lake. Spatial distribution of radiation balance of the lake surface depends on cloud regime during warm period. Radiation balance varies insignificantly because of inconsiderable changes of the cloud cover. In cold period, the distribution of radiation balance is influenced not only by the cloud cover but also by the difference in the albedo of water and snow. Therefore, the radiation balance in Northern Baikal is much lower than that in Central and Southern Baikal. Radiation balance of the water surface is a determining element in the thermal regime of the lake. Because of high water heat capacity, constant time lag is recorded in the seasonal trend of temperature parameters in comparison with radiation characteristics. Therefore, maximal accumulated radiation and radiation balance are recorded at Lake Baikal in June and the highest air and water temperatures in August.

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Fogs

Fogs at Lake Baikal form corresponding to sea fogs: they correlate with the relatively consistent seasonal drifting of air masses and with the seasonal distribution of winds. However due to the isolated inland location of the lake and the influence of the surrounding continental landmass, the Baikal fogs are to be classified as a separate type of advection fogs of large inland lakes and water reservoirs. The number of foggy days is the highest along the Northeast coast of Lake Baikal, and the lowest in the Central and the Southwest parts of the lake. The fogs lie mainly in the curves of the coastline, bays, coves, mouths of the rivers, flowing into Lake Baikal, and the numerous creek valleys that open towards the lake. In the annual cycle, the fogs are most frequent in July. The Northern stations report higher frequency of fogs in summer and register a single sharp peak in July. The Southern stations report lower frequency of fogs in the annual cycle, while the annual peak is extended over June, July and August.

At Lake Baikal, condensation prevails in summer, and evaporation – in winter. In the warm season, fogs are formed by passing of a warm front, or within a diffused pressure field above the wet underlying terrain. These fogs are formed by condensation of vapor in a mass of air warmed up above the land as it passes over the cold water. Summer fogs are very dense and persistent, especially in the first half of summer.

Evaporation fogs occur during the сold season. Until the lake freezes over, these fogs continuously stay above the water surface or can be lifted into low cloud. In winter, the Siberian Highland ground inversions accompanied by significant fall of temperature form radiation fogs. Winter fog formation is most commonly connected with advection of cold air over the warmer water surface. In cold season, as well as during the summer months, other types of fog can occur at Lake Baikal, caused by various reasons: temperature gradient between land and sea, the occurrence of floe patches and clear water surface, clearings in the fast ice of Lake Baikal.

Forecasting Baikal fogs requires an integrated approach with attention to such factors as their movability and the complexity of their formation processes. One has to take into account the general meteorological situation, the character of breeze/monsoon circulation in the area, the influence of coastline. It is important to consider the influence of West winds on the fog formation at the East coast, especially in winter.

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Cloud cover

Two maxima are recorded in the annual trend of cloud cover: summer (June-July) and pre-freeze-up (November-December). The latter prevails. The highest cloud cover values (7-8 oktas) and increased recurrence of overcast days (up to 75-80%) are registered in December on the north-eastern coast of the lake, whereas the lowest values (no higher than 4 oktas) are observed in February-March on the western shore, particularly within the territory of Maloye More (Small Sea). The foehn effect plays a significant role during the transfer of air masses over the Primorsky and Baikal Ridges, which causes a considerable drop of air humidity. In October-December, the cloud cover is very low above Lake Baikal due to the intense water evaporation from the ice free surface of the lake.

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Slope exposure

The history of depth measurements in Lake Baikal goes back to 1798, when E. Kopylov and S. Smetanin, employees of a mine plant, carried out 28 measurements between the head of the Angara river and the mouth of the Selenga river. One of such measurements yielded a maximum depth of 1,238 m. Lake Baikal was immediately recognised as the second deepest lake in the world.

In the period of 1869-1876, B. Dybovsky and V. Godlevsky compiled a detailed and precise (for that time) map of Southern Baikal, which covered 11 cross-sections. Measurements of depth were carried out from the ice, which provided high accuracy [Dybovsky, Godlevsky, 1871, 1877].

In 1902 and 1908, the Pilot Chart of Lake Baikal and Atlas of Lake Baikal were published as a result of numerous hydrographic expeditions under the leadership of F. Drizhenko, in which the depths were shown in detail for the coastal areas of the lake.

In 1925, the USSR Academy of Sciences developed a long-term project under the supervision of G. Vereshchagin to study bathymetry of Lake Baikal. This initiative resulted in the organisation of Limnological Station, later reorganised into Limnological Institute. This project helped discover the deepest place in the lake and an underwater shallow ridge named the Akademichesky Ridge, which separates the northern basin from the central one. New bathymetric maps (scales 1:300,000 and 1:500,000) were compiled. They were demonstrated at the International Limnological Congress held in Rome in 1934.

In 1962, A. Rogozin and B. Lut compiled a new bathymetric map (scale 1:300,000) as a result of long-term bathymetric expeditions. Based on this map, the Central Department for Navigation and Oceanography of the Ministry of Defence of the USSR (CDNO) published maps  “Northern and Southern Areas of Lake Baikal”  in 1973 and 1974.

In the period of 1979-1985, CDNO carried out new systematic echo-sounding bathymetric measurements throughout the entire Lake Baikal. Traverses had a spacing of 100 and 250 m in the coastal waters and 1 km in the abyssal areas. As a result of these investigations, a four-sheet bathymetric map of Lake Baikal was published in 1992 (scale of 1:200,000). To date, this is the most reliable bathymetric map of Lake Baikal. However, it has some shortcomings:

• Bathymetry is based only on some available original data;
• Bathymetry is presented by the contours of isobaths that were taken manually;
• Bathymetry is mainly represented by isobaths with a step of 100 m up to a depth of 1,000 m and 500 m for depths exceeding 1,000 m;
• Recent investigations showed that significant discrepancies can exist between true depth values and echo-sounding measurements, which are attributed to discrepancies between the real acoustic speed in Lake Baikal and the calculated rate for the echo-sounder.

In 1999, an international group of experts was organised to jointly compile a new, more precise bathymetric map of Lake Baikal. It was necessary to carry out more detailed recalculations of measurement values, which were used for maps in 1992, to digitise and adjust them to the real acoustic speed, to integrate them with the echo-sounding data obtained earlier, and to compile a new more complete computer map of Lake Baikal based on all available measurement data. This project was financially supported by INTAS (International Association for the Promotion of Cooperation with Scientists from the New Independent States of the Former Soviet Union).

The CD ROM is available with final results of this project. Coordinates of points are in a Mercator’s projection, WGS 1984 ellipsoid. The latitude for all generated maps is 53^o 0’ 00’’ N.

New bathymetric data made it possible to obtain specified morphometric information on Lake Baikal and to present it in tables. Taking into account that the lake surface is at 455.5 m a.s.l. (Baltic System of Heights), the deepest point of Lake Baikal is situated at 1186.5 m below the sea level.

The relief of the bottom of Lake Baikal is represented by isobaths with a step of 100 m. The lake consists of three basins: Northern basin – the most shallow one with a maximum depth of 904 m and an average depth of 598.4 m. Central basin is the deepest one. Its maximum depth is 1637 m, while the average depth is 856.7 m. Southern basin’s maximum depth is 1461 m with the average depth of 853.4 m. The existing Baikal depression is asymmetric: its northern and northwestern slopes are very steep, while the southern and southwestern slopes are more flat. Maximum depths are located at a distance of one third of the lake’s width from the steep northwestern slope. There is a shallow platform – a shelf - on the lake's northern and northwestern side, which is weakly developed. The shelf on the southern and southwestern coast is more pronounced.

Measurement results demonstrated that in the place of the supposed maximum depth of 1741 m, according to G. Y. Vereschagin, the actual depth is less than 1600 m - 1593-1596 m. Based on the data derived from echo sounding, the deepest part of Central Baikal is located between Cape Izhimei and Otto-Khushun. In 1972, control measurements using the NEL-5 echo-sounder showed the depth of 1637 m [Lut, 1987].

Numerous underwater works using Pisces, Mir-1, and Mir-2 submersibles offered an opportunity to visually examine morphologic and morphometric features of the underwater slopes and compare these data with the results of echo sounding. Northern and northwestern slope is sporadically covered with silt deposits with bed rock monoliths protruding between silty patches.

The steepest part of the underwater slope is located on the northern side of the depression near Cape Kolokolny, about 40 km from the southern edge of the depression. The total steepness of the slope here reaches 60-65 degrees, however, its steepness is lower than the steepness on the Baikal side of Olkhon Island by 10-15 degrees [Lut, 1987]. The steepness of northern and northwestern slopes reaches 60-40 degrees. According to the Pisces XI expedition on September 22, 1991, negative slopes at the depth of more than 700 m were observed. The steepness of the southern and southeastern slope is five to six times lower.  The average slope of the whole lake is four degrees.                                                                                                                                                                                                                                                                                                                                                     

References

Drizhenko, F. K. (1902). Pilot Chart of Lake Baikal.

Drizhenko, F. K. (1908). Atlas of Lake Baikal.

Dybovsky, B., Godlevsky, V. (1871). Report on depth measurements in Lake Baikal carried out in spring of 1871. Bulletin of the East Siberian Department of the Imperial Russian Geographical Society, 2(5). p 6-16.

Dybovsky, B., Godlevsky, V. (1877). Report on experiments in 1876 (Profiles of Lake Baikal in the appendix Bulletin of the East Siberian Department of the Imperial Russian Geographical Society, 8. p 115-135.

Lut, V. F. (1987). Morphology and morphometry of the Baikal basin. The way of knowing Baikal. Novosibirsk: Nauka. p 34-47.

Northern Area of Lake Baikal. Scale 1:300,000. (1973). Leningrad: GUNIO.

Southern Area of Lake Baikal. Scale 1:300,000. (1974). Leningrad: GUNIO.

Lake Baikal (4 sheets). Scale 1:200,000. (1991, 1992). Leningrad-St. P: GUNIO.

De Batist, M., Canals, M., Sherstyankin, P. P., Alekseev, S. P., and Teams (2002). The INTAS Project 99-1669, October 2002.