Estimation of fast ice thickness multiyear variability in the Russian Arctic seas according to polar stations data

Abstract

The warming process in the Arctic steadily continues and significantly affects the entire regime of sea ice cover development. Most of the sea ice thickness studies are based on numerical modeling and information obtained using satellite radar altimetry such that these estimations require validation by means of contact measurements. However, the comparison of data is difficult due to the irregularity and locality of measurements. This makes contact measurements at polar stations highly relevant. In this study, contact measurements were carried out by drilling for each 10-day period during winter season, they are quite accurate and have a long observations series in the same regime conditions from year to year, allowing one to assess the long-term variability of fast ice thickness. In this study, we analyzed the data series of the fast ice thickness and the surface air temperature at 16 Roshydromet land-based polar stations in the Russian Arctic Seas. The data series were taken into account from the beginning of regular measurements (the end of the 1930s, the year of the beginning varies depending on the station) to 2020 for the period November–May. Observations for the recent 15-year period (2005–2020) are compared with those prior to 2004 (from the 1930s–40s). Since 2005 sea ice thicknesses at the moment of maximum development (maximum sea ice thickness) have decreased by 13 % in the Kara Sea, by 9 % in East Siberian Sea, by 5 % in the Laptev and Chukchi Seas in comparison with the previous period. The sea ice thickness development process has become much slower, transition between the sequential stages of development is shifted by 10–20 days (in some points 30–40 days) later. The surface air temperature is on average 2,7 °C higher than for the previous period at all sea stations. The most significant changes (1.4–6.1 °C) are observed in the autumn season (October–December), all the stations show the lowest difference in the summer months. Averaged over the stations, the sum of the frost degree-days (SFDD) decreased by 14 %; all 15 recent winter seasons can be classified as mild and none of the stations has experienced winters that meet the criteria of severe winter. The frequency of mild winters increased by 36–95 % by stations. The SFDD decline is in good agreement with the changes of the mean seasonal (November-May) and maximum SIT at the stations. In conclusion, it is noteworthy that the recent 15-year period (2005–2020) is distinguished by the mildest conditions.