Fingerprints of Sea Level Rise on Changing Tides in the Chesapeake and Delaware Bays

Abstract

Secular tidal trends are present in many tide gauge records, but their causes are often unclear. This study examines trends in tides over the last century in the Chesapeake and Delaware Bays. Statistical models show negative M2 amplitude trends at the mouths of both bays, while some upstream locations have insignificant or positive trends. To determine whether sea level rise is responsible for these trends, we include a term for mean sea level in the statistical models and compare the results with predictions from numerical and analytical models. The observed and predicted sensitivities of M2 amplitude and phase to mean sea level are similar, although the numerical model amplitude is less sensitive to sea level. The sensitivity occurs as a result of strengthening and shifting of the amphidromic system in the Chesapeake Bay and decreasing frictional effects and increasing convergence in the Delaware Bay. After accounting for the effect of sea level, significant negative background M2 and S2 amplitude trends are present; these trends may be related to other factors such as dredging, tide gauge errors, or river discharge. Projected changes in tidal amplitudes due to sea level rise over the 21st century are substantial in some areas, but depend significantly on modeling assumptions.

The Tides They Are A‐Changin': A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications

“…Changes in water depth due to geocentric (or absolute) MSL rise or geological processes such as the crust's glacial isostatic adjustment (GIA) have been explored as one of the main drivers of changes in tide at the regional/global scale (Arns et al, ; Flather et al, ; Greenberg et al, ; Kemp et al, ; Müller et al, ; Pickering et al, ; Ross et al, ; Schindelegger et al, ). Tides behave as shallow‐water waves and thus are strongly affected by water depth.…”

“…With water depths adjusted for GIA and geocentric MSL changes, the model could reproduce the sign of the observed M 2 amplitude trends at 36 out of 45 analyzed tide gauge stations in Europe and Australia (Figure ), and at the North Atlantic American coasts (Figure ). Schindelegger et al () additionally reported success in capturing large fractions (order 50% or more) of the magnitude in measured M 2 changes, primarily in shallow seas dominated by frictional effects, for example, the Gulf of Mexico, the German Bight, the Northwest Australian Shelf, and the Chesapeake‐Delaware Bay system; see also Ross et al () for a comparison of tide gauge data with modeling results in the latter area. Yet changes in water depth alone appear inadequate to explain some of the very large trends seen in tidal amplitude on the European Shelf (e.g., the English Channel and the Irish Sea) as well as the Gulf of Maine.…”

“…The majority of these future tidal studies have used depth‐averaged tidal models to assess changes in the main semidiurnal and/or diurnal tidal constituents and in some cases changes in tidal high and low waters, tidal range, and other parameters (e.g., tidal currents, bed shear stress, and tidal dissipation). Only in a few exceptions have baroclinic models been used (e.g., Ross et al, ; Valentim et al, ), but this has been done only on an estuary scale. The majority of modeling studies have used finite difference grids.…”

“…Remarkably, the rates of tidal level changes observed are of similar magnitudes to the rate of mean sea level (MSL) rise at some sites; for example, Mawdsley et al () found increases in tidal range at Astoria (USA), Wilmington (USA), Delfzijl (the Netherlands), Cuxhaven (Germany), and Calais (France) of >25 cm over the last century. Furthermore, a number of modeling studies at local (e.g., Chernetsky et al, ; Familkhalili & Talke, ; Holleman & Stacey, ; Lee et al, ; Orton et al, ), regional (e.g., Arns et al, , ; Devlin et al, ; Greenberg et al, ; Idier et al, ; Luz Clara et al, ; Pickering et al, ; Pelling, Green, et al, ; Pelling, Uehara, et al, ; Ross et al, ; Ward et al, ), and global scales (e.g., Müller et al, ; Pickering, ; Pickering et al, ; Schindelegger et al, ; Wilmes et al, ) confirm that altered conditions (e.g., MSL, bathymetry, or stratification) affect tide levels and currents. Moving forward, these studies suggest that further changes to tidal levels and currents due to nonastronomical causes are possible over the 21st century and beyond.…”

Estuarine Dissolved Organic Carbon Flux From Space: With Application to Chesapeake and Delaware Bays

“…Despite these similarities in freshwater forcing, the patterns of circulation and stratification in the two estuaries differ considerably. Tidal amplitude is greater in DB, in part due to differences in shape of the two bays, funnel for DB and dendritic for CB (Ross et al, ). Stronger tides in DB and a deeper central channel in CB (Figure a) lead to DB being relatively well mixed (Sharp et al, ) and CB being partially stratified (Schubel & Pritchard, ).…”