ИСТИНА

By using operational sea ice charts (Arctic and Antarctic Research Institure, Russia)we analyzed seasonal and interannual variability of fast ice extent in the East Siberian Sea between 1999 and 2015. We identified key events in each annual fast ice cycle and linked the occurrence of these events to freezeup and melt onset and air temperature (FDDs and TDDs). The analysis reveals that fast ice in the region is sensitive to the thermodynamic processes throughout a season. On the interannual time scale we found a tendency towards shorter fast ice season. The duration of fast ice season reduces by 1.5 d/y which is in agreement with Arctic-wide trend. Analyzing fast ice annual cycle in the East Siberian Sea we describe two modes of fast regime charactered by small (S-mode) and large (L-mode) extent. By liking the occurrence of the modes to thermodynamic and dynamic factors we suggest the large fast ice extent forms during seasons with atmospheric circulating favoring sea ice import to the East Siberian Sea. This likely results in a higher rate of sea ice deformation and formation of grounded sea ice ridges which stabilize extensive fast ice cover. To confirm this hypotheses, the processes of ice ridging in the East Siberian Sea further investigated.