Portugal Current

North Atlantic currents

ThePortugal Currentis a weak ocean current that flows south along the coast ofPortugaland theIberian Peninsula.Some publications define this current as part of theCanary Current,while others distinguish it as a separate current.

The Portugal Current system is supplied mainly by theintergyrezone in the Atlantic, a region of weak circulation between theNorth Atlantic Currentto the north and theAzores Currentto the south. It is estimated, on average, to extend about 300 km beyond the shelf.

It is also influenced by the more dominant neighboringCanaryandAzoresCurrents, marking the northern extent of the Canary current. Other significant influences include seasonal winds, freshwater runoff from the Iberian Peninsula, the bottom topography found along the continental shelf break and slope, and the three main underlying water masses that are found below the seasonally variable surface layer.

General water temperatures are between 14 and 19 °C (57 and 66 °F), depending on whetherupwelling(cooler water) ordownwelling(warmer waters) dominates, thoughsea surface temperatureson the shelf have been observed to reach up to 24 °C (75 °F) in the summer and remain between 18 and 10 °C (64 and 50 °F) in the winter.

Meddies (eddiescomposed ofMediterraneanwater) are also present, particularly in the region of the Tagus Abyssal Plain (about 11-13°W; 37-39°N) and along the shelf break and also occur in some Portuguese capes: Portimão Canyon,Cape St. Vincent,Estremadura Promontory andCape Finisterre,although some appear to come from theEspinhoslope.

Upwelling conditions are favourable from the beginning of April to the end of September (peaking in July and averaging 188 days) and downwelling from the beginning of October to the end of March (averaging 177 days), particularly January and February, due to dominant wind stress along the Iberian margin,although upwelling can occasionally occur in downwelling-favourable months and vice versa, mainly due to wind variability.

Concerns about climate change

From 1941 onwards, sea surface temperature offshore Portugal has been observed to rise > 0.01 °C per year. This trend has put some seaweed species, such asLaminaria hyperborea,a kelp with an affinity for cooler water, with its distribution shifted northwards. It had its southern distribution limit atPenichein the 1970sand 1980s,but is now only limited to waters off northern Portugal, providing further support to the notion of a reduction ofkelp forestsalong the Iberian Peninsula. This increase in temperature is correlated with the decrease in the intensity of upwelling events from 1941 onwards, reducing the input of nutrient-enriched waters into the coast. Warm water species are colonizing new areas northwards while cold water species are shifting polewards,like the rustic limpet (Patella rustica).

External links

• Bischof, Barbie; Arthur J. Mariano; Edward H. Ryan (2003)."The Portugal Current System"(html).Ocean Surface Currents.University of Miami Rosenstiel School of Marine and Atmospheric Science.Retrieved2008-12-08.