Canary Current upwelling: does geographical diversity make the difference?

Abstract

The Large Marine Ecosystem of the Canary Current (CC) is one of the four major eastern boundary upwelling systems of the world ocean, and thus an area of intensive fisheries activity. The coastline is separated into two distinct areas -the Iberian coast and the NW African coast- at the Strait of Gibraltar, where the Mediterranean Sea and the Atlantic Ocean exchange water. The two areas share similarities in local oceanography, productivity and fisheries, but also exhibit their own particularities. In the northern most Iberian region, the Rías Baixas represent a unique ecosystem, strongly interacting with the coastal upwelling and amplifying its signal. Although seasonality in the Trade wind regime is more pronounced in the northern and southern extremes of the CC, the whole region exhibits high annual productivity and fish population yield. Nevertheless, a large fraction of the productivity is presumably lost to the open ocean. In particular, the NW African shelf between Cape Guir (32 N) and Cape Blanc (21 N) exhibits numerous upwelling filaments. These appear topographically generated in general and those arising south of 28 N result largely from the interplay of the coastal jet with eddies shed downstream the Canaries Archipelago. Filaments facilitate nearshore-offshore exchange of water parcels and properties and a net productivity loss. In recent years, considerable information has been gathered from these coastal ecosystems, and several review papers have been published on plankton biology, biogeochemistry or regional fisheries. Here, we present an updated global review of the CC, covering aspects ranging from hydrography, through biogeochemistry to trophic interactions and fisheries, all of which are affected by processes occurring on distances from mesoscale to large scale and over periods from days to decades. The synthesis will highlight recent major advances in experimental studies, both over the coastal shelf and in the open-ocean transition zone, as well as in modelling exercises. Ongoing numerical models range from large-scale and regional circulation off Iberia and NW Africa to coupled physical-biological models looking at plankton productivity or fish population dynamics