Afg. Fiuza et al., WATER MASSES AND THEIR CIRCULATION OFF WESTERN IBERIA DURING MAY 1993, Deep-sea research. Part 1. Oceanographic research papers, 45(7), 1998, pp. 1127-1160
The distribution of the water masses and their circulation in the east
ern North Atlantic region off the northern half of the west coast of t
he Iberian Peninsula are analysed here based on CTD measurements made
in May 1993 during the ''MORENA 1'' cruise. The upper layers of the oc
ean, down to about 100 m, showed a typical spring, non-upwelling situa
tion with a very shallow seasonal thermocline overlying thicker remnan
ts of the mixed layer from the previous winter. Below, Central Water e
xtended between a subsurface salinity maximum near depths of 100-140 m
and a salinity minimum at about 500 m. Using quantitative water mass
analysis and geostrophic calculations, a poleward surface current reac
hing down to depths of 250 m and transporting relatively warm and sali
ne Eastern North Atlantic Central Water (ENACW) of subtropical origin
was characterised, centred at a few tens of km offshore the shelf brea
k, therefore indicating that the northward current identified previous
ly in this region during winter (the Portugal Coastal Countercurrent)
continues to be present through the spring season. A large-scale trans
ition zone, the Galicia Front, was found in the northwest area of the
study region, reaching from the surface layers down to the depths of t
he Mediterranean Water. To the north of this front, relatively fresh C
entral Water of Western Atlantic origin replaced the subtropical branc
h of ENACW. At the deeper Central Water levels, ENACW from subpolar No
rth Atlantic origin was present through the whole study region. The in
fluence of the upper and lower cores of Mediterranean Water was presen
t, centred at levels of 800 and 1100 m, as indicated by their characte
ristic thermohaline maxima. The deduced flow of Mediterranean Water wa
s towards the north in the whole study region, in clear relation with
the Portugal Slope Undercurrent, and showed some tendency to branch to
wards the west through the gap between the Vigo Seamount and the Galic
ia Bank. The Mediterranean upper core occupied a relatively thin layer
, O (100 m), and underwent a strong dilution of about 45% from the sou
th to the north of the study region; the lower core spread over a larg
er depth range, of about 400-500 m, and decayed only by about 20% thro
ugh the region. Below the Mediterranean Water, the influence of North
Atlantic Deep Water spread through the study region, and an intermedia
te layer of Labrador Sea Water was also present, particularly offshore
in the northwest zone. (C) 1998 Elsevier Science Ltd. All rights rese
rved.