Extended Spectral Analysis of Tidal Variability in the North Atlantic Ocean

Abstract

Ocean tides have experienced large-scale changes over the past century, in concert with regionally variable global mean sea level (MSL) rise. Additionally, there can be coherencies between MSL and tidal fluctuations that are active at shorter time scales. This combination of water level variabilities may enhance the probabilities of exceeding flood levels under high-tide events, leading to increased frequency of short-term coastal inundation and nuisance flooding. Previous studies have established the tidal anomaly correlation (TAC) method to analyze covariability of individual tidal components and MSL in the Pacific Ocean, as well as their combination as a proxy for the change in the highest astronomical tide (δ-HAT). Here we extend this methodology to new regions and perform analyses of 170 tide gauges in the North Atlantic Ocean, considering the eight largest gravitational tides and seven overtides. Results indicate that nearly all gauges (95%) exhibit strong individual TACs in one or more tidal constituents, and over half show significant δ-HATs, with a near-equal occurrence of positive and negative tendencies. The most coherent connections of tides and MSL were found on the U.S. East Coast and in the marginal waters of Europe. At some locations, all tidal variabilities act in the same direction, which may amplify possible flood level. At other locations major parts of the tidal spectrum may counteract the MSL rise and partially mitigate extreme water levels due to tidal evolution. In either case, an understanding of regional tidal changes correlated to MSL changes can be instructive in guiding future coastal development efforts.