Determining sea level change in the German Bight

Abstract

Regional mean sea level changes in the German Bight are considered. Index time series derived from 15 tide gauge records are analysed. Two different methods for constructing the index time series are used. The first method uses arithmetic means based on all available data for each time step. The second method uses empirical orthogonal functions. Both methods produce rather similar results for the time period 1924–2008. For this period, we estimate that regional mean sea level increased at rates between 1.64 and 1.74 mm/year with a 90% confidence range of 0.28 mm/year in each case. Before 1924, only data from a few tide gauges are available with the longest record in Cuxhaven ranging back till 1843. Data from these tide gauges, in particular from Cuxhaven, thus receive increasingly more weight when earlier years are considered. It is therefore analysed to what extent data from Cuxhaven are representative for the regional sea level changes in the German Bight. While this cannot be clarified before 1924, it is found that this is not the case from 1924 onwards when changes in Cuxhaven can be compared to that derived from a larger data set. Furthermore, decadal variability was found to be substantial with relatively high values towards the end of the analysis period. However, these values are not unusual when compared to earlier periods.