ALBERT

Description: For the first time, data on stability of stationary convective filtration within infinite horizontal layer of snow covering the flat surface of floating ice is presented in this article. An analytical solution of the linearized problem was obtained with the use of the Galerkin method, and the parametric analysis of the problem was performed. It was found that the stability criteria (Rayleigh filtration numbers) obtained with consideration for the heat exchange of snow cover with the atmosphere did not exceed the known value of 4π2 for a horizontal porous layer with impermeable isothermal boundaries. As expected, the interaction with the atmosphere has the most significant impact on the critical Rayleigh numbers, while influence of variations in snow density and ice thickness and the thickness of the underlying layer of ice are small. Based on data of ice and meteorological observations made in the winter of 2015/16 in the Western part of the Laptev Sea together with calculations of the fast ice evolution, the values and temporal variability of temperature gradients and the Rayleigh numbers in the snow cover were obtained using a thermodynamic model. It was found that both, the model and observed magnitudes, exceeded their critical values determined by solving the stability problem. The conclusion is made that the convective regime of the heat transfer does really exist in the snow cover, and thus its contribution to the thermal and mass balance of sea ice during winter period should be taken into account.

Description: Results of the ice and hydrological measurements carried out in the winter of 2014/15 in theTiksiGulf(Buor-KhayaBay) are described. These data served a basis for development of a conceptual thermodynamic model of seasonal freezing of the sea water layers and underlying bottom sediments in the sea-shore zone. The model uses two methods of localization of the phase transition zones: a classical (frontal) one is used for water, while another one within the range of temperatures – for the bottom. For real atmospheric conditions, we investigated specific features of the water freezing through in the shallow coastal zone of theLaptev Sea. The quantitative characteristics of the process were obtained. The calculations demonstrated that the distinguishing feature of the process is a stabilization of the ice thickness, taking place due to essential increasing of a salinity of the sea water. As a result of this, a shallow water body does not frozen through down to the bottom at even the very low air temperatures. Cooled salt waters does not allow liquid to be frozen in pores of the bottom ground. Salinization of the under-ice water layer can cause the melting of fast ice in the shallow water with its simultaneous increase away from the coast. Ice formation in water layers and bottom sediments begins at the same time, although it proceeds differently at different depths. Due to salinization of the bottom ground a continuous frozen zone is not formed, and the whole layer of freezing precipitation is a two-phase (partially frozen) area. As a whole, the model estimates of the process parameters including the motions of the phase fronts agree with known data of direct measurements. Despite such conformity, the model data should be considered as only evaluative ones. If a bottom is flat, the horizontal mixing and advection, which are not reproduced by a one-dimensional model in principle, the actual salinity parameters will most likely not reach the calculated values. However, for small values of the tides in theBuor-KhayaBayand insignificant reverse flows of salt, effect of the last ones does not apparently exert significant influence on the intensity of cooling of the under-ice water layer as well as on the ice formation in upper layers of the bottom within such time scales as a season.

Description: Interannual changes of the summer ice coverage were investigated, and the role of hydrometeorological factors and solar activity in long-period fluctuations of the ice area in the East Siberian Sea was determined. Multivariate statistical analysis of time series of the ice cover, hydrometeorological elements, and the solar activity (SA), was performed for the period from 1950 to 2012 with regard for the cross-correlations of the analyzed variables that made possible to develop the equations of interannual fluctuations of the ice coverage in the East Siberian Sea in August and September. The equations include the following variables: air temperature in June–August of the current year TVI‑VIII; the atmospheric circulation presented by indices of Arctic oscillation (Arctic Oscillation, AO), Arctic dipole (Arctic Dipole, AD), Pacific North American oscillation (Pacific North American Oscillation, PNA); average annual runoff of river waters into the Laptev and East Siberian seas (RivLES) with a time shift of one and two years; average annual index of the North Atlantic thermal state (AMO) with a time lag of eight years; solar activity SA, presented by the average annual Wolf number with advancing of one year. Diagnostic calculations of the ice area by the obtained equations using the actual values of the indices did show a good agreement between the actual and calculated values in August and September from 1950 to 2012. These equations were used to calculate contribution of each factor to the general dispersion of fluctuations of the ice coverage. The most important factors influencing the ice cover of the Sea in August and September are: the air temperature; the atmospheric circulation, presented by the Arctic Oscillation at the end of winter; and Atlantic waters which are characterized by AMO with a time lag of eight years. The role of other factors, i.e. summer atmospheric circulation, river runoff into the above seas, and 11-year cycle of solar activity were found to be equal to only 5–10% for each. Basing on these estimates, it has been concluded that the obtained statistical equations may be used as the diagnostic models of interannual changes in the ice coverage.

Description: July and January temperatures for certain periods of the Late Pleistocene were reconstructed by Mutual Climatic Range (MCR) analysis based on 18 modern steppe and tundra species of insects, recorded in various combinations in fossil faunas of the Kolyma Lowland. Two fossil assemblages come from the sediments dated about 45000 and 35000 years ago (Karginian Interstadial), two more - from sediments of the Sartanian Glaciation stage (16000-17000 and 13000-14000 years respectively). The reconstructed summer air temperatures appear higher than modern by 1.0^.5°C in Karginian times (12.0-15.5°C) and by 1.0-2.5° in the Sartanian (12.0-13.6°C). The reconstructed range of January air temperatures is shifted towards higher values as compared to the modern; it is shown, that the MCR method reconstructs winter temperatures less adequately than summer ones. At July average temperature of about 13-14°C (that now corresponds to sparse taiga forest), joint occurrence of steppe and tundra insect species on the Arctic lowlands in the Late Pleistocene was possible only under extremely continental climate. That climate must have provided sharper temperature gradients between soil and air than today, and high contrast in thermal and moisture conditions between different units of mesoand micro-scale topography. The results confirm that during the Pleistocene, peculiar conditions of climate and landscape may have existed (usually named tundra-steppe) that supported non-analogue plant and animal communities. Our results also allow us to define boundary air temperature conditions under which those communities could exist. Communities of tundra-steppe type evolved in glacier-free continental areas of northeastern Asia as early as in the beginning of the Pleistocene.