N. G. Granin

Field studies and some results of numerical modeling of a ring structure on Baikal ice

This work presents the results of complex analysis of the field data and of mathematical modeling of the ice ring structure more than 4 km across, which was identified by the space images of South Baikal in April 2009. The measurements revealed that the ice thickness was 74 cm in the center of the structure, decreased to 43 cm at a distance of 2 km, and increased up to 70 cm and more beyond the ring. The ice water in the central part was warmer by 0.5°C and less saline (for 2 mg/kg) relative to the periphery of the structure. According to the tracer movements, the maximum velocities of the ice currents (3–4 cm/s) were observed at a distance of 2–3 km from the center of the structure with minimum ice thickness. The event was modeled using several mathematical models of various scales. The 3-D nonhydrostatic modeling of the large-scale processes on the basis of the temperature measured in the area of the structure showed the presence of local anticyclonic circulation, where the velocities of the currents increased up to the maximum (5–7 cm/s) at the distance of 2–3 km from the center and then decreased. The variations in the ice thickness in the area of the ring structure were modeled on the basis of these calculation results. The ice thicknesses determined in the context of the Stefan problem for the 2-D axis-symmetrical temperature distribution model are close to the measured ones. According to the model, the formation of the ring structure spans a period of 25–35 days. The origination of the dark ring on the satellite images is related to the lower ice thickness relative to the ambient areas and to the water level in microfractures closer to the ice surface.

Estimate of heat flux at the ice-water interface in Lake Baikal from experimental data

An original system for measuring temperature in the ice cover and subglacial water and an increase in the ice thickness provides data necessary for calculation of the heat flux at the ice-water interface. Successive freezing of 1-mm temperature sensors during the ice growth allows us to measure temperature gradients in the vicinities of the ice-water interface for the first time. An analytical equation derived from the Stefan condition allows calculations of the heat flux at the phase boundary on the basis of the experimental data, which agree with independent estimates that have been made on the basis of the subglacial temperature gradients and are within the 4–39 W/m2 range. The flow at the ice-water interface is comparable with the heat flux inside the ice depth and significantly affects the dynamics of the ice cover thickness.

Generation of lake baikal level oscillations by remote strong earthquakes

331 Examples of water level oscillations in different water reservoirs, including swimming pools, after remote strong earthquakes are well known (for exam ple, see [1–7]). However, instrumental measurements of such a level have been insufficient because the sys tems recording tides in oceans and seas and seiche oscillations in the lake water level, to filter wind driven waves, have a sampling period of a few minutes. Such a period does not allow oscillations of a smaller period to be recorded; hence, quite high frequency water level oscillations generated by earthquakes are not detected.

Oxidation of methane in the water column of Lake Baikal

The rate of aerobic oxidation of methane was calculated based on average profiles of the tritiumhelium age of the Baikal waters and concentrations of the dissolved methane in the water column. In the deep lake zone (>200 m), the intensity of oxidation vertically decreases and is (2–0.3) × 10−2 nl CH4l−1 days−1 in southern and central Baikal and (2.8–1.0) × 10−2 nl CH4 l−1 days−1 in northern Baikal. The effective coefficient of the oxidation rate in the lake depressions is 3.6 × 10−4, 3.3 × 10−4, and 3.7 × 10−4 days−1, respectively. At current methane concentrations in the water column, about 80 t of methane is oxidized per year. Oxidation of the dissolved methane in the water column was estimated at a possible increase of its concentration.

Seasonal variations in the vertical structure of pelagian water stratum in the Southern Baikal

For the first time, T,S-analysis was used to determine the specifics of seasonal variations in the vertical structure of Lake Baikal active layer. In the under-ice period, the active layer includes the under-ice, top winter, and upper intermediate water masses. The under-ice water mass, unlike other masses, shows an increase in mineralization to 100.74 mg/kg, which corresponds to a release of 71.1 g salt under 1 m2 of water surface in a layer 0–40 m in the process of salt freezing out during ice cover formation and accretion. In the phases of mixing (homothermy), the water masses of the active layer transform into a surface homogeneous mass. In summer and autumn, surface and upper intermediate water masses, separated by a water mass of summer thermocline can be identified. A specific feature of the summer thermocline water mass is the increased sum of ions because of an increase in HCO3- concentration at the decay of organic matter accumulating in the bottom part of the thermocline. The existence of the under-ice water mass and the water mass of summer thermocline was established in Lake Baikal for the first time. In the deep-water zone (>250 m), except for the bottom parts, the lower water masses (the lower intermediate and the deep) are permanent, their characteristics remaining stable during the year. The changes in the bottom water mass are due to the character of the processes of bottom water renewal.

Variations of under-ice currents in Southern Baikal by data of 2012–2016

New data on under-ice currents in Lake Baikal have been obtained with the use of high-accuracy instruments. The obtained data were used to analyze the time and space variations of under-ice currents, to calculate the coefficients of horizontal turbulent exchange and turbulent energy dissipation rates, and to derive spectral estimates of the obtained results. The estimated structures of the under-ice boundary layer near the Angara opening and far from it (up to 5 km) were compared.

A study of heat transport at the ice base and structure of the under-ice water layer in Southern Baikal

Experimental data and a new model of ice buildup are used to assess and to study variations of heat flux at the water–ice interface. The latter plays an important part in ice cover formation but still is poorly known because of the lack of field temperature measurements with sufficient spatial and temporal resolution along the phase transition boundary, which knowledge gap is filled by this study.