Large-scale changes of the semidiurnal tide along North Atlantic coasts from 1846 to 2018

• Published in: Ocean Science
• Main Authors: L. Pineau-Guillou, P. Lazure, G. Wöppelmann
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Geography. Anthropology. Recreation; G; Environmental sciences; GE1-350; Hoek; North Atlantic; North Atlantic oscillation; North East Atlantic; North West Atlantic
• Online Access: https://doi.org/10.5194/os-17-17-2021; https://doaj.org/article/448d483e96e044e4b0996ec07d2daad5

We investigated the long-term changes of the principal tidal component M 2 along North Atlantic coasts, from 1846 to 2018. We analysed 18 tide gauges with time series starting no later than 1940. The longest is Brest with 165 years of observations. We carefully processed the data, particularly to remove the 18.6-year nodal modulation. We found that M 2 variations are consistent at all the stations in the North-East Atlantic (Cuxhaven, Delfzijl, Hoek van Holland, Newlyn, Brest), whereas some discrepancies appear in the North-West Atlantic. The changes started long before the 20th century and are not linear. The secular trends in M 2 amplitude vary from one station to another; most of them are positive, up to 2.5 mm/yr at Wilmington since 1910. Since 1990, the trends switch from positive to negative values in the North-East Atlantic. Concerning the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M 2 variations in the North-East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. Our statistical analysis confirms large correlations at all the stations in the North-East Atlantic. We discuss a possible underlying mechanism. A different spatial distribution of mean sea level (corresponding to water depth) from one year to another, depending on the low-frequency sea-level pressure patterns, could impact the propagation of the tide in the North Atlantic basin. However, the hypothesis is at present unproven.