Physical Oceanography, Vol. 16, No. 4, 2006
LONG-TERM TRENDS IN THE VARIABILITY OF DEEP-WATER THERMOHALINE
CHARACTERISTICS OF THE BLACK SEA
A. B. Polonskii and E. A. Lovenkova
UDC 551.465.4+551.465.71 (262-16)
By using the archival hydrological data for 1955–1998, we analyze the trends of deep-water ther-
mohaline characteristics of the Black Sea and their interannual and decadal variability. It was
discovered that the level of salinity increased at depths greater than
in the west part of
the sea from the mid-1950-s till the early 1980s and the opposite trend was observed for the next
yr. The average rate of increase in the deep-water salinity between 1960 and 1980 and its
decrease after 1980 was equal to
yr. These facts demonstrate that the water ex-
change through Bosporus was intensified for the first
of the analyzed period and weakened
for the next
yr. The interannual variability with a typical period of
and a quasi-20-yr
periodicity are detected against the background of the parabolic trend.
The currently available data of observations do not enable us to give an adequate and complete description
of the space and time variability of large-scale deep-water characteristics of temperature and salinity of the Black
Sea. At depths greater than
even the long-term average space distributions of temperature and salinity
are studied quite poorly [1–5]. Thus, according to the data from , two closed regions with elevated salinity are
formed in the central abyssal depression, which contradicts the major part of the results published earlier [5, 6].
The long-term trends in the behavior of thermohaline characteristics at depths greater than
in fact, not studied at all. This can be explained not only by a small number of observations and their low quality
but also by the weak variability of deep-water characteristics [5, 6]. For this reason, some researchers analyze
the variability of deep-water characteristics only for certain parts of the sea and separate periods [7, 8]. Further-
more, the data of observations used in different works are often obtained for different periods of time, which
does not enable one to get the general description of the variability of deep-water characteristics of the Black Sea
on the basic time scales. Most likely, the trends revealed in different works are, to a significant extent, condi-
tioned by the presence of quasiperiodic variability on the decadal scale. This is well visible in the time depen-
dences of thermohaline characteristics at smaller depths, where the data of observations are more complete [2,
9]. It should also be taken into account that different researchers use different procedures for processing of the
experimental data. Clearly, this is true for the procedures of space and time smoothing which, in particular, leads
to the effects illustrated by the following example: The Black Sea is characterized by the presence of pro-
nounced inhomogeneities in the space distributions of the thermohaline characteristics. The major part of hydro-
logical observations is carried out in the west part of the sea for some periods of the year and in the east part of
the sea for the other periods. This leads to the overestimation or underestimation of the levels of temperature and
salinity in a given part of the Black Sea determined by using all available data without taking into account their
space and time structures and, hence, to the false low-frequency variability.
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
18–30, July–August, 2006. Original article submitted April 4, 2005; re-
vision submitted April 25, 2005.
0928-5105/06/1604–0203 © 2006 Springer Science+Business Media, Inc. 203