Nonlinear sea-level trends and long-term variability on western European coasts

Nonlinear trends and long-term variability in sea-level measured on U.K. and western European coasts with long tide gauge records (~100-200 years) are investigated. Two different analysis ethods, a standard quadratic regression and a non-parametric, Empirical Mode Decomposition, detect similar positive sea-level accelerations over the past ~150 years: 0.014±0.003 and 0.012±0.004mm/y2, respectively; these values are close to the sea-level acceleration of the global ocean over the same period as reported by several studies. Ensemble calculations with added white noise are used to evaluate the robustness of low-frequency oscillations and estimate potential errors. Sensitivity experiments evaluate the impact of data gaps on the ability of the analysis to detect decadal variations and acceleration in sea-level. The long-term oscillations have typical periods of 15-60 years and range of 50-80 mm; these oscillations appear to be influenced by the North Atlantic Oscillation and by the Atlantic Multi-decadal Oscillation. Analysis of altimeter data over the entire North Atlantic Ocean shows that the highest impact of the North Atlantic Oscillation is on sea-level variability in the North Sea and the Norwegian coasts, while the Atlantic Multi-decadal Oscillation has the largest correlation with sea-level in the sub-polar gyre and the Labrador Sea, west of the study area.