Tidal and non-tidal sea level analysis in enclosed and inland basins: The Black, Aegean, Marmara, and Eastern Mediterranean (Levantine) Seas

Abstract

Long-term water level data with 15-minute temporal resolution from 18 tide gauge stations were used to analyze tidal and non-tidal oscillations in four different seas along the Turkish coasts. High-resolution spectral analysis revealed that the semi-diurnal peaks (M2, N2, S2, K2) were higher than diurnal (O1, P1, S1, K1) in the enclosed basins: the Black, Aegean, and Levantine Seas. In the inland basin (the Sea of Marmara), however, both diurnal and mixed but mainly semi-diurnal tides were observed. Tidal ranges are the smallest in the Sea of Marmara as the basin is not large enough to generate its tide. In addition to this, the two narrow and shallow straits connecting it to the larger water bodies isolate this sea from the tidal forcing of two larger water bodies. The second smaller diurnal and semi-diurnal tidal amplitudes were observed in the Black Sea. Both it is an enclosed water body and meteorologically and hydrologically (river inflow and precipitation) the most active water body among all, the tide is masked by this these water level oscillations. Generally, there was an increasing trend in the average water level from fall to early summer corresponding to the hydrologically active period. The annual solar radiational harmonics (SA), which were in the range of 5 to 10 cm, were observed in the whole considered seas while semiannual (SSA,) harmonics, which were in the ranges smaller than 5 cm, were only observed in the Black and the Levantine Seas. The tide is minimum (∼O(10 cm)) in the Sea of Marmara and maximum in the Levantine Sea ((∼O(40–50 cm)). The contribution of the tidal harmonics to the water level energy is around one-half-fold of non-tidal ones in the easternmost part of the Levantine Sea. The largest water level ranges around 100 to 150 cm, however, observed over short periods (day to a week) due to severe meteorological conditions.