Abstract
<p>We have analyzed tide gauge data from the Adriatic Sea in order to assess the secular sea-level trend, its acceleration and the existence of possible cyclic variation. Analyzing the sea-level stack of all Adriatic tide gauges, we have obtained a trend of (1.25±0.04) mm yr<sup>-1</sup>, in agreement with that observed for the last century in the Mediterranean Sea, and an acceleration that is negligibile compared to the average global values. By means of the Ensemble Empirical Mode Decomposition technique, we have evidenced an energetic oscillation with a period of <span>∼</span>20 years that we relate with the recurrence of opposite phases in the Atlantic Multi–decadal Oscillation and North Atlantic Oscillation indices. We suggest that anomalously high sea-level values observed at all the Adriatic tide gauges during 2010 and 2011 can be explained by the rising phase of this 20 years cycle.</p>
Highlights
Inter-annual sea-level variations are caused by several mechanisms
Ocean-atmosphere oscillations are responsible for cyclic sea-level variations; at a global scale, these are primarily related to the El Niño Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Atlantic Multi-decadal Oscillation (AMO)
The power of the oscillation with the longest period (IMF10, 70.5 years) exceeds that of all the other IMFs with k>4. This is a manifestation of the “red spectrum” problem in tide gauge observations illustrated by e.g. Sturges and Hong [2001], which substantially hinders the detection of a genuine sea-level trend from records shorter than ∼60 years [Douglas 1997]
Summary
Inter-annual sea-level variations are caused by several mechanisms. These include ocean mass variations, primarily related to the melting of present-day continental ice sheets and glaciers, and volume changes, mostly produced by thermo- and halo-steric processes [see, e.g. The problem of sea-level rise in the Adriatic Sea has been tackled in a number of studies, based on both tide gauges observation and oceanographic models. Since the tide gauges with longest records are located in the northern Adriatic (Venice and Trieste, Italy), most of the studies have focused on this area [see for example Ferla et al. We apply the Empirical Mode Decomposition (EMD) method to the Adriatic sea-level curve obtained by stacking, and, for the first time in this region, we enlighten the existence of cyclic sea-level variations related with the NAO and the AMO modes. The locations of the 30 RLR tide gauges considered in this study are displayed, which shows the number of valid years of data from each station (a valid year is one for which ≥10 monthly averages are available).
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