Aegean Sea-Level Variability in the Past Half-Century Based on Tide Gauge Data

Abstract

Global sea-level rise induced by global warming has been growing in importance as a research topic in the past few decades. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) has strongly emphasized a visually certain trend in the sea-level rise in the past two centuries. Many studies have addressed the trend in sea-level records, both in global and regional scale, as studying the trend renders it possible to make future predictions. The latest study of World Climate Research Programme Global Sea Level Budget Group determined the global sea-level rise between 1993-2018 as 3.1 mm/year. The Aegean as a regional sea is chosen for this study to compare if there are any similarities between the global tendency and the regional using tide gauge records of monthly mean sea-levels in selected 6 stations. The data used in this study were obtained from the Permanent Service for Mean Sea Level (PSMSL), which is an organization that collects and publishes tide gauge records from across the world. The gaps in the raw tide gauge data were imputed by Kalman filtering, the time series were decomposed by using STL decomposition and the loess smoothed trend lines were obtained. The data ranges of time series were divided into 2 segments (from 1969 to 1995 and from 1995 to the end date) and linear trends for each segment were determined as well as the whole duration for each station. Mann-Kendall, Cox-Stuart, and Spearman’s Rho tests were applied on the datasets to detect statistically significant trends. The sea-level trends varied for each station and depending on the segment taken into consideration. 2 negative and 2 positive trends were obtained for the first segment. Positive trends changing from 1.6 mm/year to 7.5 mm/year with an average of 3.7 mm/year were determined for the second segment’s results of all stations.