M. N. Shimaraev

Upwellings in Lake Baikal

Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10−2−6.5 × 10−2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800 m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.

Modern climate changes and deep water temperature of Lake Baikal

This paper presents the results on measurements of water temperature in Lake Baikal of 1972–2007. The abnormal warming during this period was accompanied by gradual increase of the upper 300 m layer temperature, but did not affect the water state of the deep zone. Temperature fluctuations in 1972–1992 mainly depended on dynamic influence of atmosphere on the water column causing inter-annual changes in the activity of deep convection.

Specific features of cold bottom intrusion in Baikal according to observations in 1993–2009

The specific features of cold bottom intrusion in Baikal are considered based on the results of observations of 1993–2009. It is shown that the intrusion-related renewal of bottom water takes place not regularly and not simultaneously in different hollows. Its maximums were recorded in Southern Baikal in 1997 and 2007, in Middle Baikal in 1995, 2006, and 2009, and in Northern Baikal in 1997 and 2009. In these years, the volume of cold bottom layer in some hollows reached 200–470 km3 and its total cooling reached −20 to −60 MJ 109. Cold intrusions were more frequent and had greater effect on the bottom layer in Southern Baikal than in other parts of the lake. The intrusions, especially in the years of their active development, are shown to cause water cooling in both the bottom layer and the major part of the deep-water zone of all hollows.

Renewal of deep waters of Lake Baikal revisited

The patterns of renewal of bottom waters in Lake Baikal under the influence of deep convection and intrusion of cold waters have been considered based on the data of temperature surveys of Lake Baikal conducted in 1993–2009. The volumes of the cold bottom layer with the maximums of 200–470 km3 in individual years and the values of its total cooling (−20–60 × 109 MJ) have been determined for South, Middle, and North Baikal. The renewal process is asynchronous and proceeds with different activity in these parts of the lake, which indicates that the mechanisms that cause deep convection in the context of the great latitudinal length and differences in the climate and hydrological processes manifest themselves regionally. The volume of intrusions has been determined. Its average value for the period was higher in South Baikal (20 km3) than in Middle Baikal (9.8 km3) and North Baikal (8.6 km3). The volume of the intrusions in these parts of the lake was 30–70 km3 in some years.

on the vertical distribution of microorganisms in lake baikal during spring deep-water renewal

The vertical distribution of microorganisms during spring deep-water renewal in Lake Baikal was studied. The downward advection of trophogenic waters was found to create conditions for the extensive growth of microorganisms capable of decomposing and mineralizing organic carbon, nitrogen, and phosphorus in deep water layers. These processes occur annually at spring thermal bars near the underwater slope of Lake Baikal, whereas in its pelagic zone, the deep intrusions of waters rich in organic material are observed only in the years when enhanced deep-water renewal is accompanied by a high spring yield of phytoplankton.

The influence of deep convection on aeration of the bottom zone in Baikal

We investigated the influence of deep forced temperature convection on aeration of the bottom water layer in the pelagic zone of Baikal. Temperature T (± 0.002°C) and oxygen O2 concentration (± 0.01 mg/L) were measured by using the SBE-25 probe with the SBE-43 oxygen sensor in May-July 2006−2007 and 2009−2013. Oxygen input into the bottom layer with cold intrusions was determined for 79 cases. The study revealed a quantitative correlation between the heat deficit and the rise in oxygen content in the bottom layer during cold intrusions. This correlation was used to reconstruct the values of intrusion aeration of the bottom layer during 1993−2005. It is ascertained that the intrusion-caused 2006−2013-average oxygen input into Baikal’s bottom layer is virtually close to the annual oxygen demand for oxidation processes in the water column and bottom sediments. In the southern and middle parts of Baikal, intrusion-caused input of oxygen corresponds to a higher rate of its demand (4.5−4.6x10-4 mg/L per day). A slight increase in oxygen concentration was detected in the bottom layer of the South and Middle Baikal and a slight decrease in the bottom layer of North Baikal during 1993−2013.

Concordance of interannual variability in ice regime of Baikal and lake Ladoga

We examine the dependence of the ice conditions for two major lakes of Asia and Europe: Baikal and Ladoga, on regional values of the arithmetic sums of mean daily winter air temperatures and global atmospheric processes expressed by atmospheric circulation indices. By ranking the winters according to the sums of mean daily winter air temperatures, it was possible to identify winters of the same type of severity for the regions of Baikal and Ladoga. The winters of the same type show an enhancement in correlations between ice characteristics with respect to the sums of winter air temperatures and atmospheric circulation indices as well as ice characteristics of the two lakes. It is shown that the interannual changers in characteristics of ice regime of Ladoga and Baikal are largely determined by the same atmospheric processes. The role of the circulation is most clearly manifested in variation of temperature regime indicators. Thus, the sums of air temperatures accumulated during a winter in the regions of these lakes show primarily the closest correlation with the Arctic and North Atlantic oscillation indices.