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.
Highlights
The water masses in the eastern North Atlantic have been studied for over 30 years, since the 1974 pioneering work by Fernando Fraga and collaborators (Fraga 1974, Manríquez and Fraga 1982, Fraga et al 1985, Ríos et al 1992), leading to a much improved description of their characteristics and distribution
A remarkable local feature of South Atlantic Central Water (SACW) is the relatively low dissolved oxygen values, which respond to the high primary production in the surface layers combined with enhanced remineralization during the long recirculation times in this eastern basin, precisely around the Guinea Dome. This is clear in the vertical profiles of those stations within (E41) and south (E54 and E70) of the Cape Verde Frontal Zone (CVFZ), where we find that SACW is characterized by a minimum in oxygen between 100 and 500 m
By using the lower central waters, the intermediate waters, and the deep water (NACWL, SACWL, SACW*, Mediterranean Water (MW), Antarctic Intermediate Water (AAIW), and North Atlantic Deep Water (NADW)) we find that only 16% of the data above σθ = 27.32 have a percentage of NADW higher than 10%, with an absolute maximum of 17%
Summary
The water masses in the eastern North Atlantic have been studied for over 30 years, since the 1974 pioneering work by Fernando Fraga and collaborators (Fraga 1974, Manríquez and Fraga 1982, Fraga et al 1985, Ríos et al 1992), leading to a much improved description of their characteristics and distribution. Las masas de agua del Atlántico Norte oriental han sido estudiadas por más de 30 años, desde los trabajos pioneros de Fernando Fraga y colaboradores iniciados en 1974 (Fraga 1974, Manríquez y Fraga 1982, Fraga et al 1985, Ríos et al 1992), dando como resultado una gran mejora en la descripción de su distribución y características.
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