Meridional changes in water mass distributions off NW Africa during November 2007/2008

Abstract

ABSTRACT. An optimum multiparameter analysis was applied to a data set for the eastern boundary of the North Atlantic subtropical gyre, gathered during November of two consecutive years and spanning from 16 to 36º N. This data set covers over 20º of latitude with good meridional and zonal resolution over the whole coastal transition zone. The contribution from six water types in the depth range between 100 and 2000 m is solved. In the 100 to 700 m depth range the central waters of southern and northern origin meet abruptly at the Cape Verde Frontal Zone. This front traditionally has been reported to stretch from Cape Blanc, at about 21.5º N, to the Cape Verde Islands, but in our case it penetrates as far as 24º N over the continental slope. South of 21º N latitude we actually find a less saline and more oxygenated variety of South Atlantic Central Water, which we ascribe to less diluted equatorial waters. In the 700 to 1500 m depth range the dominant water type is a diluted form of Antarctic Intermediate Water (AAIW), whose influence smoothly disappears north of the Canary Islands as it is replaced by Mediterranean Water (MW); at latitudes where both water masses coexist, we observe MW offshore while AAIW is found near-shore. North Atlantic Deep Water is the dominating water type below about 1300/1700 m depth south/north of the Canary Islands; this abrupt change in depth suggests the existence of different paths for the deep waters reaching both sides of the archipelago.

The continental slope current system between Cape Verde and the Canary Islands

“…1a). Pastor et al (2012) emphasized that the top 300 m south of the CVFZ have characteristics close to equatorial waters, therefore being even more distinct from NACW.…”

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

“…The last criterion is repeated until the difference between two consecutive mean salinity values in each temperature bin is less than 10%. North Atlantic Central Waters (NACW) in the Canary Basin extend down to about 600 m, with salinity values decreasing with depth down to 35.5 and phosphate concentrations increasing with depth up to 1.05 µmol kg −1 (Pastor et al 2012). AAIW are located immediately under the NACW (at the depth interval 600<z<1000 m and the neutral-density interval 27.2<γ n <27.65 kg m −3 ), being recognizable through a salinity minimum (salinities are less than 35.5, or fresher than the deepest NACW) and an intense phosphate maximum (concentrations are well in excess of 1.25 µmol kg −1 ) (Machín et al 2006, Machín and Pelegrí 2009, Pastor et al 2012.…”

“…AAIW are located immediately under the NACW (at the depth interval 600<z<1000 m and the neutral-density interval 27.2<γ n <27.65 kg m −3 ), being recognizable through a salinity minimum (salinities are less than 35.5, or fresher than the deepest NACW) and an intense phosphate maximum (concentrations are well in excess of 1.25 µmol kg −1 ) (Machín et al 2006, Machín and Pelegrí 2009, Pastor et al 2012. Meddies in the Canary Basin are located immediately below the AAIW level (1000<z<1500 m and 27.6<γ n <27.8) (Biescas et al 2008), and are characterized by positive salinity anomalies (values as high as 36.5) and negative phosphate anomalies (concentrations as low as 0.7 µmol kg −1 ) (Pastor et al 2012).…”

“…The hydrographic and nutrient cruise data were collected as part of the field activities of the projects CANIGO (Parrilla et al 2002) and CANOA (Pastor et al 2012), aimed at elucidating critical features of the region's large-scale circulation and variability. In January 1997, during the Meteor-37 cruise (R/V Meteor as part of the CANIGO project), a meddy (hereafter M37) was detected near (32.2°N, 12.2°W) (Fig.…”

Meridional and zonal changes in water properties along the continental slope off central and northern Chile

“…It is an inverse modelling technique widely used to study the distribution of water masses at scales where the properties are approximately conservative (classic approach) (e.g., Tomczak and Large 1989, Pérez et al 2001, Tomczak and Liefrink 2006, Silva et al 2009, Pastor et al 2012. In this subsection we briefly revise the basics of the OMP technique, while in the following two subsections we give a more detailed discussion of its implementation for our study area.…”