Climate Changes in Temperature and Salinity of the Aegean Sea

Based on the reanalysis MEDSEA_REANALYSIS_PHY_006_009 data, the interannual variability of temperature and salinity of the Aegean Sea at depths from 1.5 to 209 m was investigated for 1955–2015. An increase in the average temperature of the Aegean Sea during the study period was found at depth till approximately 100 m. At deeper levels, neutral and negative temperature trends were found. The average growth rate of sea temperature at the surface was approximately 0.01°С per year. Since the surface temperature has increased more strongly and more evenly in space than at depth, this increase may be associated with regional warming. At the same time, the salinity of the Aegean Sea did not change significantly during the study period. Against the background of an average increase in the temperature of the upper layer of the Aegean Sea, its fluctuations were found at various periods, the main of which is approximately 18.6 years. This period can be associated with the lunisolar nutation of the Earth’s axis of rotation, which affects the tides and mixing of waters, in particular, in the Aegean Sea. This is confirmed by the fact that the maximum energies of fluctuations in the salinity of the Aegean Sea on time scales from 1 to 30 years are located exactly on the period of 18.6 years. Teleconnections of temperature and salinity fluctuations in the Aegean Sea for a period of 18.6 years with the Pacific Decadal Oscillation (PDO), which are also significantly affected by the lunisolar nutation of the Earth’s rotation axis, have been found. Another reported period of temperature fluctuations in the Aegean Sea is approximately 11.5 years, and may be associated with an 11-year cycle of solar activity and with the internal dynamics of Eastern Mediterranean. The spectral peaks of the Aegean Sea temperature were found at periods of 8, 4, and 2 years also. They can be associated with the North Atlantic Oscillation (NAO), which has a period of 8 years. The spectral peaks at periods of 4 and 2 years can be 1:2 and 1:4 super-harmonics of the nonlinear effect of NAO on the Aegean Sea. Also, fluctuations in the temperature of the Aegean Sea were found for periods of 4.8, 3.6, and 2.4 years. These periods are characteristic of the El Niño – Southern Oscillation (ENSO), and they may be sub-harmonics of the Chandler wobble of the Earth’s poles over a period of about 1.2 years, which, through pole tides, can affect both El Niño and the Aegean Sea.