Monthly mean sea levels in Greece during 1969–1983 compared to relative vertical land movements measured over different timescales

Abstract

Sea level data from 16 tide gauge stations in Greece have been used in an analysis of the seasonal cycle of mean sea level in Greek waters together with an investigation of the interannual variability of sea level in the region for the period 1969–1983. The recorded seasonal cycle is found to vary considerably across the area and to agree well with sea level observations from neighbouring coastlines. The Greek data result in knowledge of the mean sea level seasonal cycle being now available from throughout the northeastern Mediterranean. An overall drop of sea levels is observed during the mid-1970's, while the larger peaks and dips in the records are found to be coherent over the whole area and, on several occasions, to be general to the entire northern Mediterranean. The tide gauge data set has also provided measurements of the secular trends in relative mean sea levels over the same 15-year period. A wide geographical variation of sea level trends is observed spanning a range from +21 to −11 mm/yr (measured relative to sea levels at Katakolon). After inversion, these measurements provide estimates of relative vertical land movements of the present epoch which can be compared to those obtained from archaeological and geological sources, i.e. changes over timescales of thousands, tens of thousands and tens of millions of years. Differences in the sign and magnitude of the relative vertical land movements of this geologically complicated region obtained from the different data sets are discussed in detail. It is shown that the direction of vertical movement recorded by the tide gauges correlates well with that observed over longer periods and that, with relatively few exceptions, sites which are uplifting (submerging) relatively rapidly over one timescale are uplifting (submerging) relatively rapidly at all timescales. While the rate of vertical movement throughout the Aegean and southern Greece usually preserves the same sign at a given site over timescales of 10 1–10 7 yrs, its magnitude decreases approximately by a factor ( 1 T ) 0.4 , where T is the measurement averaging period.