Inter-decadal variability of the Black Sea surface and cold intermediate layer temperature

 A.M. Novikova, A.B. Polonsky

 Institute of Natural and Technical systems, Russian Federation, Sevastopol, Lenin St., 28

Email: anelkapi@bk.ru

DOI: 10.33075/2220-5861-2018-4-110-115

UDC 004.657, 004.043

Abstract:

    The long-term variability of the Black Sea surface and the intermediate layer waters temperature is analyzed on the basis of updated database for the period from 1951 to 2017. Temperature fields over the ten-year periods on the surface (February-March) and horizons of 50, 75, and 100 m (annual average values) are restored at the nodes of the regular grid. From these data, quantitative estimates of ten-year temperature variability of the upper 100-meter layer were obtained. The presence of inter-decadal temperature variations within the period of 40-50 years and the amplitude of up to 0.8°C was confirmed. A common trend has been identified for all horizons – a sharp rise in temperature over the past 20 years, significantly exceeding its maximum values, observed in the middle of the 20th century.

     The range of inter-decadal variations in the surface temperature in the winter season was 1.6°C, the average annual at depths of 50 m – 1.4°C, 75 m – 0.9°C, 100 m – 0.6°C. There was also an increase in the average temperature of the cold intermediate layer (CIL), which reached 8°C in the mid-2000s and continues to grow mainly due to the sea surface temperature increase in winter, when CIL water is renewed.

     A tendency of lowering the CIL boundary to a depth of 75 m during periods of warming (1961–1975 and 2006–2017) and its rise to a depth of 50 m during the cooling period (1986–2000) has been revealed. Comparison of temperature fields during periods of inter-decadal highs and lows showed that at the depth of 100 m the temperature field is influenced by the cyclonic structure of the Black sea rim current (BSRC), with the dome rising of warmer deep-water waters in the central part of the sea and lowering of subsurface cold waters along the 100-meter isobaths both during periods of temperature maxima, and at the minimum temperature. At the depth of 75 m, a similar field structure was observed only during the minimum period, when the BSRC was intensified due to the increase in the frequency of atmospheric cyclones over the southern and central parts of the sea, which was accompanied by the rise of warmer deeper waters. During periods of temperature maxima, the descent of the CIL to a depth of 75 m was caused by a weakening of cyclonic activity directly above the sea, with its simultaneous increase over the land in the northern part of the Black Sea region, as well as the number of anticyclones in the southern part of the water area.

      All this indicates a significant contribution of atmospheric processes in the formation of the thermal structure of the waters of the Black Sea, including CIL.

Keywords: GIS, the Black Sea, temperature, inter-decadal variability, CIL

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