A century of tidal evolution around the Panama Canal

As one of the most vital passageways worldwide, the Panama Canal plays essential roles in global trade and maritime logistics. Sea levels around the Panama Canal are dominated by ocean tides but local tidal evolution is still unexplored to date, which motivates present study. Two secular tide gauges longer than 110 years (Cristobal and Balboa) around the Panama Canal are analyzed to explore multi-time scale tidal variability. It is found that observed nodal modulations of major constituents are generally consistent with the equilibrium tidal theory. M₄ and Mf nodal modulations notably deviate from the theory possibly due to non-linear processes. Long-term trends exist in main semi-diurnal tides, while main diurnal tides do not have significant secular trends. It is worth mentioning that M₄ and MS₄ amplitudes at Cristobal have halved in the past century. Moreover, tidal parameters of major constituents at Cristobal and Balboa show abnormal mutations in 1908, 1990–1998, and 2013–2018. As a result of changing tides, tidal asymmetries at Cristobal are significantly weakened while the number of high tides per year is notably decreased. Tides at Balboa are almost symmetric. Tidal regimes at Cristobal can periodically shift between mixed diurnal tides and mixed semi-diurnal tides following the 18.61-year nodal cycle. However, such regime shift has disappeared since 1997 due to secular negative trends in M₂ amplitudes. In general, the findings of this study can be helpful for ships navigating in the Panama Canal.