Abstract
Upwelling and downwelling processes play a critical role in the connectivity between offshore waters and coastal ecosystems, having relevant implications in terms of intense biogeochemical activity and global fisheries production. A variety of in situ and remote-sensing networks were used in concert with the Iberia–Biscay–Ireland (IBI) circulation forecast system, in order to investigate two persistent upwelling and downwelling events that occurred in the Northwestern (NW) Iberian coastal system during summer 2014. Special emphasis was placed on quality-controlled surface currents provided by a high-frequency radar (HFR), since this land-based technology can effectively monitor the upper layer flow over broad coastal areas in near-real time. The low-frequency spatiotemporal response of the ocean was explored in terms of wind-induced currents’ structures and immediacy of reaction. Mean kinetic energy, divergence and vorticity maps were also calculated for upwelling and downwelling favorable events, in order to verify HFR and IBI capabilities, to accurately resolve the prevailing surface circulation features, such as the locus of a persistent upwelling maximum in the vicinity of Cape Finisterre. This integrated approach proved to be well-founded to efficiently portray the three-dimensional characteristics of the NW Iberian coastal upwelling system regardless of few shortcomings detected in IBI performance, such as the misrepresentation of the most energetic surface dynamics or the overestimation of the cooling and warming associated with upwelling and downwelling conditions, respectively. Finally, the variability of the NW Iberian upwelling system was characterized by means of the development of a novel ocean-based coastal upwelling index (UI), constructed from HFR-derived hourly surface current observations (UIHFR). The proposed UIHFR was validated against two traditional UIs for 2014, to assess its credibility. Results suggest that UIHFR was able to adequately categorize and characterize a wealth of summer upwelling and downwelling events of diverse length and strength, paving the way for future investigations of the subsequent biophysical implications.
Highlights
Upwelling (UPW) and downwelling (DOW) phenomena represent a key role in the strong physical connectivity between offshore waters and coastal ecosystems
According to the results derived from the annual comparison of filtered high-frequency radar (HFR) hourly time series against independent in situ current observations (Figure 2), it can de concluded that the HFR system performance was reliable for 2014, operating within suitable ranges and in line with the typical values previously reported in the literature (Table 3)
The first focus was placed on the synergistic blend of multi-platform observations and the CMEMS IBI ocean forecast system, working in concert to adequately depict the main oceanographic features of two persistent UPW and DOW events in the NW Iberian coastal system during summer 2014
Summary
Upwelling (UPW) and downwelling (DOW) phenomena represent a key role in the strong physical connectivity between offshore waters and coastal ecosystems. Wind-driven coastal UPW has been extensively studied along the eastern edges of the world’s major ocean basins, as it has relevant implications on biogeochemical activity and global fisheries production [1,2]. UPW episodes commonly last 3–10 days [3,4] and can alternate with weak-wind periods (relaxation) or even DOW-favorable events where poleward winds induce a net onshore displacement and subduction of surface coastal waters, allowing larvae communities to reach suitable locations and recruit to the shoreline. Notwithstanding, extremely active and persistent UPW and DOW events can impact negatively on coastal ecosystems. The opposite-phase circulation patterns during DOW-favorable wind conditions may be related to the transport and retention of pollutants onto the shoreline, with subsequent biological and socioeconomic consequences
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
