Fixed-point time series, repeat survey and high-resolution modeling reveal event scale responses of the Northwestern Iberian upwelling

The hydrography and circulation of the Northwestern Iberian Margin (NWIM) was studied over an annual cycle from November 2008 to December 2009. The study was focused on the Cape Silleiro border region that separates the rugged northern coastline of the Rias Baixas embayments and the smoother southern coastline, a source of major fresh water outflows. Monthly across-shelf transects off Cape Silleiro monitored hydrography and currents, while an upward-looking ADCP registered currents in 72 m depth on the shelf over the period. To provide greater detail of the variability both spatial and temporal, during the annual cycle, a ROMS-AGRIF configuration of the region was built. Validation of the model against the observations produced robust results that reproduced many aspects of the observed variability. It was therefore possible to examine features of the NWIM, such as the seasonal cycle, wind-induced upwelling and downwelling and their associated horizontal circulations, as well as nearshore countercurrents related to freshwater plumes, in unprecedented detail. Five different scenarios were investigated in the study year through examination of characteristic physical processes: (1) late autumn up welling, (2) high energy winter conditions, (3) spring upwelling-downwelling cycles, (4) summer upwelling, and (5) autumn transition to high energy conditions. The demonstration of the robust capacity of this model configuration, to reproduce in detail the phenomena observed in this region, suggests that the physical model could be reliably extended to other years in order to provide the basis for multidisciplinary studies in relation to biogeochemical cycles and harmful blooms. Other applications could include transport of sediments, larvae, microplastics and other contaminants as well as operational application for general ocean forecasting.

Automated summary

The hydrography and circulation of the Northwestern Iberian Margin (NWIM) were studied over an annual cycle, with a focus on the Cape Silleiro border region. The model validation showed that it could reproduce many aspects of the observed variability, providing a basis for multidisciplinary studies.