Can Tidal Perturbations Associated with Sea Level Variations in the Western Pacific Ocean Be Used to Understand Future Effects of Tidal Evolution?

Abstract:

This study examines connections between mean sea level (MSL) variability and diurnal and semidiurnal tidal constituent variations in the western tropical Pacific Ocean, a region showing anomalous MSL rise over the last 20 years and strong inter-annual variability. MSL fluctuations are found to be correlated to tidal amplitude and phase fluctuations at 13 of 17 open-ocean and 7 of 9 continental shelf tide gauges, after de-trending the time series. Twenty statistically significant tidal anomaly trends (TATs) in both phase and amplitude are found for the two largest tidal constituents, K1 (diurnal) and M2 (semidiurnal). Smaller constituents (O1 and S2) show significant trends at nearly half of all gauges. MSL fluctuations are concurrent with shifts in tidal amplitudes and phases, and both positive and negative relations are observed. Changing overtides suggest TATs are influenced by changing shallow water friction over the equatorial Western Pacific and the eastern coast of Australia (especially near the Great Barrier Reef). At stations around the Solomon Islands, a strong connection is observed between semidiurnal TATs and changes in thermocline depth, overtide generation, and the El Niño Southern Oscillation (ENSO). TATs for O1, K1, and M2 are related to each other in a manner that is consistent with resonant triad interactions. Since the response of tides to MSL variability is spatially complex and frequency dependent; short-term responses may not predict long-term behavior.