ISSN 0001-4370, Oceanology, 2011, Vol. 51, No. 2, pp. 221–230. © Pleiades Publishing, Inc., 2011. Original Russian Text © V.B. Piotukh, A.G. Zatsepin, A.S. Kazmin, V.G. Yakubenko, 2011, published in Okeanologiya, 2011, Vol. 51, No. 2, pp. 232–241. 221 1. INTRODUCTION The investigation of the marine environment’s response to the long-term changes in the atmospheric forcing represents an important oceanological prob- lem related to the forecasting of the consequences of climatic variations for the ecosystem. This problem is particularly urgent for the Black Sea, where life exists exclusively in the upper aerobic layer about 200 m thick (hereinafter, referred to as the active layer). It is subjected to the influence of the atmospheric pro- cesses, while the marine ecosystem and biological pro- ductivity are sensitive to changes in the hydrophysical conditions of the basin [4] and, specifically, in the thermohaline characteristics [15, 16]. A lot of studies are dedicated to the variability of the thermohaline characteristics of the Black Sea’s active layer and to the physical processes that condi- tion this variability at synoptical to seasonal scales [1, 13, 15]. However, the knowledge of the long-period (interannual or decadal) variability and its relation to the winter cooling is rather limited and concerns mainly the sea’s surface temperature (SST). A descrip- tion of the interannual and quasi-decadal variability of the SST is given in a number of recent works [2, 6, 8, 9, 15]. The interannual variability of the temperature and salinity at the surface and at a depth of 100 m, along with the temperature in the core of the cold intermediate layer, (CIL) was investigated in [7, 9, 17]. The first attempts to reveal the mechanisms of the coupling of the long-term variability of the SST with 3 3 the large-scale atmospheric forcing were undertaken in [11, 12]. Acknowledging the validity of the results obtained thanks to the above works, it should be noticed that, having in mind the impact of climatic changes upon the marine ecosystems, it is important to understand the processes of the transfer of the climatic signal into the water’s thickness and its influence on the hydrol- ogy of the upper layer. As is known, intensive cooling and vertical convective mixing occurs in the Black Sea in the winter, which results in the maximal thickness and minimal temperature of the upper quasi-homoge- neous layer (UQL). This is accompanied by the for- mation of basic features of the CIL. During the warm seasons, the latter is separated from the UQL by a sea- sonal thermocline whose depth ranges from 5 to 30 m. The thermocline blocs the vertical mixing and mark- edly isolates the CIL from the atmospheric forcing during the warm seasons. For these reasons, the ther- mohaline’s characteristics at depths of 30–40 m and deeper “remember” the winter cooling in the warmer seasons. This influences the features of the distribution and biological productivity of the phytoplankton sen- sitive to the density stratification. Additionally, the strength of the winter mixing determines the level of the enrichment of the UQL with the nutrients from the underlying layers which, in turn, influences the intensity of the subsequent development of the plank- tonic communities [4, 16]. Impact of the Winter Cooling on the Variability of the Thermohaline Characteristics of the Active Layer in the Black Sea V. B. Piotukh a , A. G. Zatsepin a , A. S. Kazmin a , and V. G. Yakubenko b a Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia E-mail: vbp@ocean.ru, zatsepin@ocean.ru, akazmin@ocean.ru b Southern Branch of the Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia E-mail: v_yakub@mail.ru Received November 5, 2009; in final form, December 28, 2010 Abstract—The influence of the winter atmospheric forcing on the interannual variability of the Black Sea’s active layer’s thermohaline structure during 1982–2008 is investigated. The results are based on the combined analysis of the hydrological measurements from a ship, satellite measurements of the sea’s surface tempera- ture (SST), and the NCEP/NCAR reanalysis data for the surface air temperature (SAT). A high correlation between the variability of the winter mean SST/SAT and the thermohaline characteristics of the active layer during the following warm season was found. It is shown that the winter atmospheric forcing significantly affects the variability of the temperature, salinity, and density down to the 150–200 m depth, and this has to be considered in the analysis of the interannual and long-term variability of the Black Sea’s active layer. DOI: 10.1134/S0001437011020123 MARINE PHYSICS