Main results

The global ocean circulation structure over a period of 1000 years was reconstructed by using numerical simulation with a World Ocean circulation model [E.Golubeva, Numerical Analysis and Applications,2010]. Under climatic forcing on the ocean surface, the numerical model reproduced the major features of the wind and thermohaline global largescale water circulation. The sensitivity of the global circulation to temperature-salinity anomalies on the ocean surface over time intervals of 100 years was investigated. The numerical experiments performed in the paper have shown that the variability of the global meridional ocean circulation can be determined by the thermohaline conditions on the ocean surface in the North Atlantic polar regions. However, the overall pattern of the global conveyor remains stable. Desalinization of the subpolar circulation waters decreases the intensity of formation of the North-Atlantic deep water. This is accompanied by slowing down of the interocean water exchange. The temperature and salinity anomalies that increase the convective activity in the North Atlantic enhance the global exchange of the World Ocean waters. An important conclusion from the experimental results is that increasing intensity of the meridional water circulation is accompanied by increasing horizontal water circulation in the subtropical circulation systems. It should be noted that the process of baroclinic adjustment of the global ocean to changes in the intensity of deep water formation in the North Atlantic polar latitudes takes place in the model mainly during the first 50 years, and the process of adaptation of water dynamics to enhancement of convective mixing is faster than that in the opposite case.
According to the model calculations with the existing distribution of sources on the ocean surface, the temperature and salinity anomalies in the Pacific Ocean do not have a considerable effect on the global water circulation. Only extremely high anomalies can lead to the appearance of a deep water source in the Pacific Ocean and subsequently weaken or destroy the global conveyor belt.

Numerical modeling of the Arctic Ocean ice system response to variations in the atmospheric circulation from 1948 to 2007. . The numerical experiment, performed on the basis of the SibCIOM for the period 1948–2007 by using NCEP/NCAR and CIAF atmospheric data, allowed us to reproduce the climate changes in the Arctic Ocean caused by variations in the atmospheric circulation. The results of numerical experiments are the following.

1. The two main regimes of the ice-cover circulation in the Arctic Basin are reproduced:cyclonic and anticyclonic regimes conditioned by variations in theatmospheric circulation.
2. According to experimental data, the beginning of changes in the water circulation of the Arctic Ocean corresponds to the mid-1970s, which coincided with the first positive signal of the initiated positive NAO phase.
3. During the negative NAO phase in the period 1960–1980, in line with the anticyclonic water circulation, the Canadian Basin is characterized by the formation of a wide low-salinity lens corresponding to the accumulation of freshwater flowing from rivers. In the subsequent period of the positive NAO phase, which facilitates the evolution of cyclonic motion of waters, the accumulated freshwater reserve flows into the northern Atlantic through the Canadian Archipelago channels and the Fram Strait.
4. According to the numerical calculations, because of the initiation of the positive NAO phase, the flow of Atlantic waters into the Arctic Basin is enhanced, the boundary between the Atlantic and Pacific waters is shifted eastward, the water circulation in the Canadian Basin turns from anticyclonic to cyclonic, the temperature of the ocean intermediate layergrows, and the ice cover is reduced.

Modeling the long-term and interannual variability in the Laptev Sea hydrography and subsea permafrost state. The focus of the presented study is the variability of the hydrology of the Laptev Sea. The study analyzes results from three-dimensional coupled ice-ocean regional models of different horizontal resolution. The Laptev Sea circulation and its interannual variability are simulated on the basis of a large-scale model of the Arctic and North Atlantic. The second model is a nested ocean model focused on the Lena River Delta surroundings with an enhanced grid resolution. Both models are forced by the NCEP/NCAR Reanalysis. The simulated high variability of summer circulation over the Laptev shelf is mainly caused by the difference in the local prevailing wind patterns. The analysis of the Lena river model tracer pathways shows that in summer, the pronounced offshore or onshore transport occurs in certain years, while generally, the circulation pattern is much more complicated being subject to wind forcing, position of the ice edge, and intensity of the river runoff. When the cyclonic circulation of the atmosphere is predominant, the heat and fresh water anomalies, formed due to the sea surface fluxes and the river runoff, penetrate down to the bottom layers. The model results suggest that the response of winter hydrography to the variability of atmospheric circulation is less pronounced. The salinity pattern, formed during the autumn period under the influence of the wind, persists for a long period during winter and gradually changes under the influence of sea-ice formation processes and on contact with the adjacent water areas.

Our simulations show that there was an increase in the near-bottom temperature in the Laptev Sea shelf. The heat flux of the Lena River plays a significant role in this process. The warming of near-bottom waters on the Laptev Sea shelf deserves special attention due to its potential impact on the submarine permafrost, formed during the last glacial cycle, when the Arctic shelf was above sea level. We have performed numerical simulations of the subsea permafrost evolution and the present-day state on the East Siberian Arctic Shelf, using near-bottom temperature provided by the ice-ocean model. Our simulation estimates that the thickness of the permafrost within most of the shelf is 180-550 m, given the geothermal flux value of 60 mW/m 2 . These results show the permafrost upper boundary deepening by ~0.5-5m from 1948 to 2014 (≤ 7.5 cm/yr) in the shelf. The degradation rate from above is the most rapid in the near-shore coastal zone of the shelf and in the areas affected by the Lena River outflow. Based on the simulations performed, we state that the current warming is not able to destabilize undersea permafrost on the shelf of the Laptev Sea.