Hydrological Structure, Circulation and Water Mass Transport in the Gulf of Cadiz

Abstract

Hydrological and LADCP data from four experiments at sea (Semane 1999(Semane , 2000(Semane /1, 2000(Semane /3, 2001) are used to describe the structure and circulation of Mediterranean Water in the Gulf of Cadiz. These data were gathered on meridional sections along 8˚20′W and 6˚15′W and between these longitudes on a zonal section along 35˚50′N. The mesoscale and the submesoscale structures (Mediterranean Water Undercurrents, meddies, cyclones) observed along these sections are characterized in terms of thermohaline properties and of velocity. The transports of mass and salt in each class of density (North Atlantic Central Water, Mediterranean Water, North Atlantic Deep Water) are computed with an inverse model. The model indicates a general eastward flux in the Central Water layer, and a westward flux in the Mediterranean Water layer, but there is also a horizontal recirculation and entrainment in these two layers, as well as strong transports associated with the meddy and cyclone found during Semane 1999.

Quasi-synoptic transport, budgets and water mass transformation in the Azores–Gibraltar Strait region during summer 2009

“…Our estimates of the contribution of each central water source to entrainment (derived from net transport inFigure 10)are:-0.5 Sv of ENACW P : the net ENACW P incoming transport across the CAIBOX sections, which should be entirely entrained, as it does not flow across the Gibraltar Strait;-0.1 Sv of ENACW T from the north of the box: 0.38 Sv that reaches the Gulf of Cadiz in the Gulf of Cadiz current, minus 0.3 Sv that flows in the Gulf of Cadiz Current into the Mediterranean Sea (according to Péliz et al, 2009); -0.22 Sv of ENACW T from the AC: 0.72 Sv that is available to reach the Gulf of Cadiz in the AC current minus 0.5 Sv of offshore central water flowing into the Mediterranean Sea (according toPéliz et al, 2009).The total entrainment is thus 0.8 Sv; if we also consider the 0.3 Sv of ENACW T being downwelled and pulled out of the box by MW, the total amount of central water being subducted would be 1.1 Sv. Addition of this entrained central water to the 0.77 Sv of MOW results in ~1.6 Sv of MW, in good agreement withAlves et al (2011).…”

“…As it flows southwards off the Portuguese coast, its salinity is expected to increase by diapycnal mixing with the underlying MW (van Aken, 2000). Therefore, and in view of the upper and lower limits of the straight ENACW line given by Alves et al (2011), we took the mean salinity values representative for both central waters in the Gulf of Cadiz region as 36.4 psu for ENACW T and 35.62 psu for ENACW P . In addition, we chose 38.4 psu for the MOW (as given by García-LaFuente et al, 2011).…”

Arms winding around a meddy seen in seismic reflection data close to the Morocco coastline

“…Locally, they can be steered by topography. When generated at Portimão Canyon, meddies often drift in the Gulf of Cadiz either to the Southwest or cyclonically to the Southeast along the mean circulation [Alves et al, 2011]. The further evolution of meddies exiting the Gulf of Cadiz southwestward has not yet been observed.…”

Evidence of Mediterranean Water dipole collision in the Gulf of Cadiz

“…This program carried out seven experiments at sea in November 1995, July 1997, July 1999, July 2000, November 2000, July 2001, and July 2002 (the latter experiment was carried out by IFREMER). Long CTD-LADCP sections across the Gulf were performed during these cruises and the results are described in other papers [Quentel et al, 2011;Alves et al, 2011]. These experiments also included XBT-XCTD cross sections of eddies, previously detected by altimetry or via other hydrological sections.…”