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

• Published in: Ocean Science
• Main Authors: Pineau-guillou, Lucia, Lazure, Pascal, Woppelmann, Guy
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union (EGU)
• Subjects: geo; envir; North Atlantic; North Atlantic oscillation; North East Atlantic; North West Atlantic
• Online Access: https://doi.org/10.5194/os-17-17-2021; https://archimer.ifremer.fr/doc/00635/74732/74722.pdf; https://archimer.ifremer.fr/doc/00635/74732/80073.pdf; https://archimer.ifremer.fr/doc/00635/74732/

We investigated the long-term changes of the principal tidal component M2 over the North Atlantic coasts, from 1846 to 2018. We analysed 9 tide gauges with time series starting no later than 1920. 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 M2 variations are consistent at all the stations in the North East Atlantic (Newlyn, Brest, Cuxhaven), whereas some discrepancies appear in the North West Atlantic. The changes started long before the XXth century, and are not linear. The trends vary from a station to another; they are overall positive, up to 0.7 mm/yr. Since 1990, the trends switch from positive to negative values. Concerning the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M2 variations in the North East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. We discuss a possible underlying mechanism. A different spatial distribution of water heights 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.