Tidal Variability Related to Sea Level Variability in the Pacific Ocean

Ocean tides are changing worldwide for reasons unrelated to astronomical forcing. Changes in tidal properties coupled with altered mean sea level (MSL) may yield higher peak water levels and increased occurrence of short-term exceedance events, such as storm surge and nuisance flooding. Here we investigate the hypothesis that changes in relative sea level are correlated with alterations in tidal amplitudes. Our approach focuses on the correlation between short-term (monthly to interannual) fluctuations in sea level with changes in tidal properties of major ocean tides (M-2, and K-1; S-2 and O-1) at 152 gauges. Results suggest that sea level variability is correlated to interannual tidal variability at most (92%) of tide gauges in the Pacific, with statistically significant rates between 10 and 500 mm per meter sea level rise observed. These tidal anomalies, while influenced by basin-scale climate processes and sea level changes, appear to be locally forced (in part) and not coherent over amphidromic or basin-wide scales. Overall, the Western Pacific shows a greater concentration of tide/sea level correlations at interannual time scales than the Eastern Pacific; 44% and 46% of gauges are significant in K-1 and O-1 in the west compared to 29% and 30% in the east, and 63% and 53% of gauges in the west are significant in M-2 and S-2 versus 47% and 32% in the east. Seasonal variation in tidal properties is less apparent in the empirical record, with statistically significant seasonal variations observed at only 35% of all gauges, with the largest concentrations in Southeast Asia. Plain Language Summary It is common knowledge that sea level are rising worldwide, due to climate change. Less known, and less studied, is the variability of ocean tides that has also been occurring in past decades. Tidal changes are unexpected, since the tides are based on predictable astronomical motions. Nevertheless, these changes are observed worldwide. Sea level changes along with tidal changes, when combined, can have serious implications for future coastal flooding. This study performs a survey of Pacific Ocean tidal variability to understand which regions are experiencing the greatest tidal changes.