Shelf–ocean exchanges in the Canaries–Iberian Large Marine Ecosystem
Oceanic regions like the Canaries–Iberian Large Marine Ecosystem (LME) have an importance disproportionate to their area because the wind–driven upwelling of nutrient–rich sub–surface waters into the photic layer promotes a blooming of phytoplankton, leading to high secondary production, large stocks of economically important exploitable species, and general enhancement of biogeochemical activity including the exchange of the greenhouse gas CO2 and other fluxes. Unlike other coastal upwelling regions, the oceanic waters adjacent to the Canaries–Iberian LME experiences considerable subduction, because of the Mediterranean Water formation in the Strait of Gibraltar. This phenomenon causes a pronounced heterotrophy in the mesopelagic (thermocline) waters of the surrounding area. At the same time, the narrow but extended coastal upwelling system can export its excess production to the impoverished epipelagic (surface mixed layer) ocean waters by means of upwelling filaments that extend hundreds of kilometres offshore. Despite various investigations of such coastal transition zones, definitive knowledge of the resultant exchange of water parcels, gasses, dissolved and suspended organic and inorganic materials and planktonic biota between near–shore and open ocean is still lacking. In this project we aim to provide a NEW LEVEL OF UNDERSTANDING of the time–varying horizontal and vertical exchanges of water parcels and their properties between the upwelling/productive Canaries–Iberian LME and the subducting/oligotrophic open ocean. Through intensive inter–disciplinary OBSERVATIONS and MODELLING in two areas of recurrent and persistent filament systems we will determine how mesoscale interactions between upwelling, current jets, filaments, and eddies govern the fate of water parcels and their dissolved, particulate and planktonic content as they pass through the coastal transition zone. The two contrasting systems selected are the filament at 42oN, which develops in the summer upwelling off the fishing ground of Cape Silleiro and that at 30oN, which persists in the year round upwelling off the fishing ground of Cabo Guir (Morocco).