Wave Regime and Wave-Current Coupling in an Upwelling-Driven Bay: Seasonal and Inter-Annual Variability

Data from an acoustic Doppler current profiler (ADCP), a wave-gauge, a met-ocean buoy and model results provide new insights into the wave regime in a partially sheltered upwelling-driven bay, the Ria de Vigo (NW Iberia), and the adjacent continental shelf from June 2013 to August 2014. Swell on the NW-Iberian shelf comes mainly from NW directions, while wind sea comes from the NW under upwelling conditions, and from the SW under downwelling conditions. As the ria is protected from the NW and exposed to the SW, swell is almost always attenuated when entering the bay, and wave height inside the ria depends mostly on shelf wind sea variability. During the upwelling season, swell and wind sea barely enter the ria and wave heights inside the ria are small (0.21 m). During the downwelling season, shelf wind sea directly enters the ria, contributing more to the total wave height which achieves its maximum values (0.46 m). There is a cumulative action of wave and currents (wave current coupling, WCC) that is stronger during the downwelling season. The WCC entails an increase in the seabed energy which could reinforce bottom remineralization. The inter-annual variability (2009-2016) of winter wave height and WCC in the ria is associated with the combined role played by the North Atlantic Oscillation (NAO) and West Europe Pressure Anomaly (WEPA) indices. The highest waves and strongest WCC occur during the coincidence of negative NAO and positive WEPA phases and can have potentially relevant repercussions on the ecosystem services of the ria.