Climatic changes of thermal condition in the Kara sea at last 40 years

Abstract

The paper discusses air (Ta) and sea surface temperature (SST) year-to-year variability due to warming of the Kara Sea, using the data from regular observations at the meteorological stations Roshydromet (GMS) in 1978–2017, NOAA optimum interpolation and reanalysis data. We use the methods of cluster, correlation analysis and Empirical Orthogonal Functions (EOF). We investigate possible cause and effect relationships of these changes with the variations of the wind field components, climatic indices and the sea ice concentration field. The cluster analysis of the three main EOF components has allowed us to identify four areas on the basis of the nature of changes of the water temperature anomalies field. The climatic changes in these areas, in the coastal and island zones of the Kara Sea have manifested themselves in the steady increase of the annual air temperature at GMS from 0,47–0,77 °C/10 years on the southwest coast to 1,33–1,49 °C/10 years in the north of the sea. This is equivalent to warming from 1,9 to 6,0 °C in the last 40 years. For the open sea the value of the Ta trend is about 1,22 °C/10 years, which corresponds to an increase in the average Ta by 4,9 °C in the last 40 years. This value is approximately 3 times greater than that for all the Northern hemisphere for the same period.Annualy, the maximal trend was observed in November and April mainly and exceeded 2–3 °C/10 years at some of the stations. We identify anomalously warm (2016 and 2012) and anomalously cold (1978, 1979, 1992 and 1998) years: the warmest year was 2012, the coldest — 1979. Positive SST trends were observed over all the sea area during the warm period of year (to 1 °C/10 years). SST increased to 2,4 °C, which is approximately 1,5 times greater than the corresponding SST values for the Northern hemisphere. The maximum SST trend (0,4 °C/10 years) was observed in the northwest and southwest parts of the sea. From June to August the trends of SST exceed the annual ones 1,5–2 times. Interannual SST and Ta variations are characterized by close correlation links. Until approximately 1998–2004 the warming was rather insignificant, and after that the growth rate of Ta and SST increased many fold. Apparently it indicates changes in the mode and the large-scale atmospheric circulation in the early 2000s. We also observed a trend of strengthening of the southern wind during the cold period of the year and the northern one — in the warm period (0,5–0,6 m/s in 40 years). It is shown that there is a close correlation between the Ta increase and the changes in the meridional component of the wind speed during the cold period of the year for all the sea areas. For the warm period it is statistically insignificant both for Ta and SST. For the cold season we observed a contribution of the large-scale mode of atmospheric circulation into the variability of V component of the wind speed. The conribution was expressed through the indeces NAO, SCAND, Pol/EUR, AZOR, ISL and the differences of ISLSIB. For the warm season this contribution is expressed through the NAO, SCAND and AO only. For the warm period we showed statistically significant correlation between the increase in SST, Ta and the processes parametrized by the AMO, EA/WR and AZOR indeces. For the cold period the indeces are AMO, Pol/Eur, SIB and ISL SIB. The interannual variations of the sea ice concentration field are characterized by close correlation with Ta changes both in the annual cycle and during the periods of ice cover formation and evolution (R = –0,7... –0,9). For these periods we showed statistically significant relationships between the first EOF mode fluctuations and two climatic indeces — AMO (R = 0,5) and Pol/Eur (R = 0,4). The relationships between the temporary variability of the sea ice concentration and the wind field characteristics are weaker and statistically significant only for the meridional component of the wind speed (R = –0,4).