The chemistry of Mediterranean outflow and its interactions with surrounding waters

Abstract

Abstract The spreading of the Mediterranean water (MW) and its interactions with the surrounding waters are described and discussed in terms of oxygen and nutrient patterns in the Gulf of Cadiz and off the southern Portuguese coast, in winter of 1998. Low concentrations of nutrients and relatively constant levels of dissolved oxygen, by comparison with those of the surrounding waters, were associated with the warm and saline MW outflow. Three cores of the MW have been identified, the deeper core presenting higher nutrients and lower dissolved oxygen concentrations than the upper two cores. Closer to the Strait of Gibraltar the MW remained pressed against the continental slope, while to the west the cores spread horizontally offshore. At the deeper MW layers some irregularities were noticed in the nutrient fields, apparently associated with the complex topography of the Portimao Canyon. The North Atlantic Central Water (NACW) and the North Atlantic Deep Water (NADW) were chemically identified in the area. A water mass displaying a well-defined minimum of O 2 (157 μmol kg −1 ) and high concentrations of nutrients have been detected, entrained approximately from 750 to 1000 m depth, and lying between the two main MW cores inshore, and overlying the lower core of MW offshore. It is suggested that this water mass is a remnant of the Antarctic Intermediate Water (AAIW).