engleski

Is bidecadal sea-level oscillation amplifying in a part of the Mediterranean Sea?

As shown by Unal and Ghil (1995), long-term variability of the Mediterranean sea level is dominated by decadal signal in the west and extreme east parts of the basin and by bidecadal signal in the Adriatic Sea located in between. Adriatic bidecadal oscillation was detected already by Polli (1947) in the Trieste and Venice tide-gauge data, and was more recently observed in time series collected at four Croatian stations – Rovinj, Bakar, Split, and Dubrovnik (Orlić and Pasarić, 2000). In the latter paper it was stressed that the oscillation does not represent the nodal tide, since neither the amplitude nor the phase agree with the theoretical values for the equilibrium nodal tide, but that it may be related to global bidecadal signal. As documented by Mann and Park (1996), this signal manifested itself in the Mediterranean area in low air pressure and low air temperature in the early 1950s, 1970s, and 1990s, (i.e. at the time of low sea levels). Moreover, the time of high/low sea levels coincide with the Mediterranean sea temperatures being high/low (White and Cayan, 1998) and the salinities being low/high (Lascaratos, 1998). Tide-gauge measurements performed in the Adriatic after these studies confirmed the existence of bidecadal oscillations. They also pointed to an apparent amplification of the signal. Since it is recorded at all Adriatic stations, the amplifications appears to be a realistic feature that demands an adequate explanation. Obviously, a proper interpretation of the modulation necessitates that the bidecadal variability itself be understood, and this is crucial to differentiating natural climate changes from those due to anthropogenic forcing.

Mediterranean Sea; bidecadal variability; climate changes

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