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et al. 2002). This layer mixes with surrounding waters, moves northwards and extends westwards to the Island of Tenerife (HERNÁNDEZ-GUERRA et al. 2003). The deepest layer has its origin in the Mediterranean Sea. This very saline European Mediterranean Water (EMW) lies deepest directly above the bottom (HERNÁNDEZ-GUERRA et al. 2003; KNOLL et al. 2002) and entrains layers of the same density. The flow of the different water masses varies seasonally. In spring and summer the Canary Current is strongest, with SW and NACW yielding the highest intensity of southward transport in spring, turning to flow northwards in summer and autumn (HERNÁNDEZ-GUERRA et al. 2003; JOHNSON and STEVENS 2000; KNOLL et al. 2002). The current strength of the AAIW is strongest during autumn (KNOLL et al. 2002), when northward transport is at a minimum (HERNÁNDEZGUERRA et al. 2003). Furthermore, a permanent counter current exists within the Canary Current at a depth of about 200 – 400 m (KNOLL et al. 2002; MITTELSTAEDT 1983).This counter current is mainly due to a compensating force in the horizontal water distribution. The south-eastern region of the North East Atlantic is characterised by an excess of water due to the equatorial counterand undercurrent transporting water to the east. Simultaneously, a deficit of water along the northern African west coast occurs as the Canary Current flows westwards away from the coast. This forces the water from the equator to the north (MITTELSTAEDT 1983). With few exceptions, the counter current usually does not reach the inshore region, but if it reaches the coast it can become subsurface or even surface (MITTELSTAEDT 1983; vAN CAMP et al. 1991). The counter current is strongest during summer since the equatorial counter current is most intense then and therefore provides an excess of water. Adding to this effect, the Canary Current itself is strengthened by powerful trade winds, so the counter current does not reach to the surface (MITTELSTAEDT 1983). But during autumn the trade winds are weakest, causing the northward current to often reach the surface at the slope (KNOLL et al. 2002). Nevertheless, southward winds exist and the velocity of the surface counter current does not exceed a few cm per second, while the deeper layer reaches a velocity to 5 – 10 cm per second (MITTELSTAEDT 1983). In the water street west of the Canary Islands between the islands and the West African coast, which is called La Bocaina, the northward counter current down to 500 m is strongest with up to 9 cm per second in autumn (KNOLL et al. 2002). Counter currents may also interrupt the coastal upwellings and may be influence the circulation of the upwelling waters along the West African coast (MITTELSTAEDT 1983). These upwellings are caused by the strong trade winds blowing from the northeast parallel to the coast line (ARÍSTEGUI et al. 1997; JOHNSON and STEVENS 2000; vAN CAMP et al. 1991). At the level of the Canarian Archipelago, the winds blow parallel to the coast favouring a strong upwelling, while in the north, the winds blow onshore, keeping the upwellings weak (NAVARRO-PÉREZ and BARTON 2001; vAN CAMP et al. 1991). The winds advect the surface waters from the coast due to shear force, but the entire wind force cannot be transmitted to the deeper layers, causing the overall water flow to be directed about 45° from the wind direction (Ekman transport).Therefore, the water flows directly to the west. Due to the movement of water towards the open ocean and the decreasing depth towards the shelf, water flowing onshore is forced upwards (MITTELSTAEDT 1983), thus creating upwelling.The upwelling water reaches the surface on the shelf break or over the mid shelf and frequently occurs inshore as well (MITTELSTAEDT 1983). The upwelled waters originate at a depth of 100 – 200 m (KNOLL et al. 2002), have temperatures of 15 – 17°C and can be traced up to 200 – 300 km from the shelf break in upwelling regions north of Cape Blanc (MITTELSTAEDT 1983). Consequently, the upwelled water causes a gradient in salinity and temperature with the surrounding surface waters from the east to the west. At the level of the Canary Islands, the temperature increases due to insolation, while the salinity decreases

Inf. Téc. Inst. Canario Cienc. Mar. n°13


Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  
Spatial and seasonal patterns in species composition of fish larvae in the Canary Islands  

Technical report consisting on a comprehensive annotated larvae taxa list with the most important taxonomic characters of this region