FUTURE SEA LEVEL RISE AND CHANGES ON TIDES IN THE ARGENTINEAN CONTINENTAL SHELF

SIMIONATO, C. G.; LUZ CLARA TEJEDOR, M.; D'ONOFRIO, E.E.; MOREIRA, D.

Puerto Madryn

Conferencia; 9th International Conference on Tidal Sedimentology ? Tidalites 2015.; 2015

Centro Nacional Pagatonico y Asociacion Argentina de Sedimentologia

The aim of this work has been to provide estimations of the future tide conditions under diverse SLR scenarios for the Patagonian Shelf. The environmental, societal and economic implications of tidal changes are wide ranging; including coastal flooding, tidal renewable energy generation, sediment transport, shipping, coastal and bottom morphology, location of tidal mixing fronts and inter-tidal habitats. Therefore, those changes demand further investigation by continued analysis of historical data sets and by numerical modeling; the larger-scale ones might be of major geophysical significance, but even the regional and local ones need to be understood as far as possible if the insights obtained are to be incorporated into the tidal prediction schemes and tidal models needed for many practical purposes (Woodworth, 2010).To achieve the proposed goals, we have performed a set of numerical simulations applying the regional model MARS (Model for Applications at Regional Scales), developed at the French Institute for Exploitation of the Sea (IFREMER) (Lazure and Dumas, 2008; Lazure et al., 2009). This model reproduces the present tides with a high degree of accuracy providing confidence to the estimation of the potential future changes.It has been shown (Pelling and Green, 2012; Pelling, Green and Ward, 2013; Ward, Green and Pelling, 2012) that the way in which tidal models are used for the investigation of the impact of SLR can cause significant differences between the results. When vertical walls are added at the present coastline, the changes are due to (subtly) changed properties of the propagating wave as the water depth is altered, whereas when flooding of existing land is allowed, the response is also controlled by the newly introduced dissipation in the new cells (Pelling, Green and Ward, 2013). The inundation of low-lying land cells can also alter the resonant properties of the basins (Pelling and Green, 2012). Because of this reason, prior to the analysis of the impact of SLR on tidal propagation, we studied the impact of including the flooding in the simulations for the particular case of the Patagonian Shelf. The coastline here is characterized by high cliffs and becomes low only northward 40° S, where it is dominated by beaches and wetlands. In addition, the tidal wave propagates northward in the Southern Hemisphere (Simionato et al., 2004), reaching those last low areas only after having gone over the Patagonian Shelf. Because of this reason, the way in which SLR is implemented has little impact in the solutions southward San Blas. Northward this location the response is highly affected by the added dissipation in the inundated cells, driving to a much lower response on tidal amplitudes over the Buenos Aires Province.In what regards the impact of the SLR on tidal amplitude and phase, similar studies have been addressed for other areas of the world ocean (e.g. Pelling and Green, 2013; Pickering et al., 2012; Ward, Green and Pelling, 2012) and our results are quantitatively similar to them, in the sense that large changes in tidal properties are to be expected if the SLR also results extreme. A comparison of the simulations for SLR scenarios of 1, 2 and 10 m show that the response of M2 amplitude (Table 1 and Figure 1) is non linear, particularly in the areas close to San Blas and Cabo Blanco. The largest increment occurs in the area that spans between San Blas and Golfo San José, for the 10 m scenario, with a value that reaches 0.76 m. In all the cases, the amphidromes displace offshore, to the east/northeast, with the SLR. This is the case even with the degenerated amphidrome of the Río de la Plata.In 24 of the 27 stations analyzed, the change in the spring tidal range is larger than in the neap range for the 1 m of SLR scenario. This occurs in 23 of the 27 stations for the 2 m of SLR scenario and the change in the spring tide is larger than in the neap tide at all the stations except for Monte Hermoso for the 10 m of SLR scenario. Considering significant changes of more than 5 %, they occur in 4, 10 and 18 of the 27 studied stations for the 1, 2 and 10 m of SLR scenarios, respectively. Changes greater than 10 % occur, instead, in 3, 4 and 13 stations, respectively.The most important absolute changes are observed in the stations where the tidal range is larger, excepting the coastal area southward Punta Quilla. To the south of San Antonio Este, the tidal constituent S2 has a large influence in the change of the tidal range, whereas northward that station (except for Monte Hermoso), the contribution of O1 and K1 is more than that of S2.Together with a generalized increment of the tidal amplitudes over most of the Patagonian Shelf, an increase of tidal currents also occurs. This and the flooding of land areas drives to a global increment of the tidal dissipation by bottom friction with SLR over that area, which reaches 16% for the extreme case of 10 m SLR.The simulations suggest that SLR will significantly influence the tidal fronts of the Patagonian Shelf. Results indicate that the global area affected by vertical mixing tends to reduce with the SLR in 1.6, 2.7 and 8.2 % for the 1, 2 and 10 m scenarios. Nevertheless, whereas the frontal areas of Cabo Blanco and San Sebastián tend to reduce, those of Península Valdés tend to increase. The most sensitive region is Cabo Blanco, where the reduction in the vertically mixed areas are of -2.8, -4.4 and -21.9 % for 1, 2 and 10 m SLR, respectively.The physical mechanisms which explain the observed modifications in the tidal regime are the changes with the SLR of: (i) the speed of the tidal wave, (ii) the Rossby radius of deformation, (iii) the energy dissipation by bottom friction and (iv) the resonant properties of the basin. They produce the migration of the amphidromes and complex non-linear patterns of change in the tidal waves.