We used a satellite-derived global daily sea surface temperature (SST) dataset with resolution 0.25 × 0.25${}^{\circ }$ to analyze interannual changes in the Arctic Shelf seas from 2000 to 2020 and to reveal extreme events in SST distribution. Results show that the second decade of the 21st century for the Siberian Arctic seas turned significantly warmer than the first decade, and the increase in SST in the Arctic seas could be considered in terms of marine heatwaves. Analyzing the spatial distribution of heatwaves and their characteristics, we showed that from 2018 to 2020, the surface warming extended to the northern deep-water region of the Laptev Sea 75${}^{\circ }$ to 81${}^{\circ }$N. To reveal the most important forcing for the northward extension of the marine heatwaves, we used three-dimensional numerical modeling of the Arctic Ocean based on a sea-ice and ocean model forced by the NCEP/NCAR Reanalysis. The simulation of the Arctic Ocean variability from 2000 to 2020 showed marine heatwaves and their increasing intensity in the northern region of the Kara and Laptev seas, closely connected to the disappearance of ice cover. A series of numerical experiments on the sensitivity of the model showed that the main factors affecting the Arctic sea-ice loss and the formation of anomalous temperature north of the Siberian Arctic seas are equally the thermal and dynamic effects of the atmosphere. Numerical modeling allows us to examine the impact of other physical mechanisms as well. Among them were the state of the ocean and winter sea ice, the formation of fast ice polynias and riverine heat influx.

The paper investigates the role of atmospheric circulation in the surface layer in forming the Arctic ice structure. For the analysis, the empirical orthogonal function (EOF) method of decomposition of the surface wind field is used, and the reaction of ice to changes in the principal components of leading EOF modes is investigated using statistical methods. Analyzing the rate of ice change in the Arctic associated with the Arctic ocean oscillation mode, we concluded that this mode’s variability leads to the formation of a seesaw in the ice field between two regions. From the one side, it is the region of the central deep-water part of the Arctic, including the East Siberian Sea, and from the other side, it is all other marginal seas. The second (“dipole”) mode is most associated with an increase/decrease in the ice thickness at the Arctic exit through the Fram Strait, as well as the formation of the so-called “ice factory” in the coastal region of the Beaufort Sea in the positive phase of this mode. There is also a significant relationship between the variability of third mode and the arrival of Atlantic waters with a high heat content into the Arctic through the Barents opening, which creates preconditions for ice formation in this region.

The characteristics of the eddy mass transport are estimated depending on the values of the parameters of a large-scale flow that forms under the conditions of the shelf seas in the Arctic. For this, the results of numerical simulation of the Kara Sea with a horizontal resolution permitting the development of mesoscale eddies are used. The parameters resulting from numerical experiment are considered as a statistical sample and are analyzed using methods of sensitivity study and clustering of sample elements. Functional dependencies are obtained that are closest to the simulated distributions of quantities. These expressions make it possible, within the framework of large-scale models, to evaluate the characteristics of the cross-isobatic eddy mass transport in the diffusion approximation with a counter-gradient flux. Numerical experiments using the SibCIOM model showed that areas along the Fram branch of the Atlantic waters trajectory in the Arctic as well as the shelf of the East Siberian and Laptev seas with adjacent deep water areas are most sensitive to proposed parameterization of eddy exchanges. Accounting for counter-gradient eddy fluxes turned out to be less important.

The characteristics of eddy mass transport are estimated depending on the values of the parameters of a large-scale flow that forms under the conditions of the shelf seas in the Arctic. For this, the results of numerical simulation of the Kara Sea with a horizontal resolution permitting the development of mesoscale eddies are used. The multiple realizations of eddy mass flux resulting from a numerical experiment are considered as a statistical sample and are analyzed using methods of sensitivity study and clustering of sample elements. Functional dependencies are obtained that are closest to the simulated distributions of quantities. These expressions make it possible, within the framework of large-scale models, to evaluate the characteristics of the cross-isobathic eddy mass transport in the diffusion approximation with a counter-gradient flux. Numerical experiments using the SibCIOM model showed that areas along the Fram branch of the Atlantic waters trajectory in the Arctic as well as the shelf of the East Siberian and Laptev seas with adjacent deep water areas are most sensitive to the proposed parametrization of eddy exchanges. Accounting for counter-gradient eddy fluxes turned out to be less important.

The main source of summer heating of the upper layer of Siberian Arctic shelf seas is shortwave solar radiation. The radiation flux attenuates as it passes through the water depth, and the attenuation rate is determined by the optical properties of water, which mainly depend on the concentration of suspended matter in the water. In numerical models of the ocean and sea ice, the process of shortwave solar radiation absorption is described by different parameterizations. In this work, the sensitivity of the numerical 3D regional ocean and sea ice model SibCIOM to two parameterizations of the penetrating radiation is studied: (1) two-component parameterization with constant attenuation coefficients for the infrared and visible spectral regions depending on one of ten ocean water transparency classes; (2) three-component parameterization with different absorption coefficients for the red, green, and blue parts of the visible spectrum, which is based on satellite data on chlorophyll concentration. The analysis of the results of numerical experiments for the water area of Siberian shelf seas has shown that if the seasonal distribution of chlorophyll concentration is taken into account when simulating a penetrating shortwave radiation flux with the RGB parameterization, then regions of water warming are formed in the surface or bottom layer, which differ from a basic experiment with the two-component parameterization. The comparison between the simulation results with observations shows the RGB parameterization to be preferable for the numerical simulation of Arctic shelf seas.