Hydrography of a transatlantic section from Portugal to the Newfoundland Basin

Abstract

Hydrographie data (salinity, temperature, oxygen, silicate, and phosphate) obtained on 5 stations ("Meteor" cruise 23, leg C, 8 to 26 June 1971) on a section from Lisbon, Portugal, to 44° N, 43° W (Newfoundland Basin) by both water sampling and in situ observation by the "Bathysonde" (STD), are summarized. A strong core of Mediterranean water was found at the eastern boundary of the section (38.5° N, 11.5° W). At this station, the core is accompanied by low nutrient concentrations and brings about an extended oxygen minimum (ca. 500 to 1400 m depth). The core quickly weakens towards the west and is, at the Mid-Atlantic Ridge, only apparent in the Bathysonde data. Two salinity maxima are observed within the core of Mediterranean water, the center of which speads along the isopycnal σt = 27.7. Dissolved oxygen shows a rapid concentration increase with depth below the Mediterranean water core; concentration variations with depth below the range of this increase are only small. The mean deep-water oxygen concentration increases from 5.5 ml/kg (below 2500 m) to 6.20 ml/kg (below 1500 m) in an east-west direction on the section. The upper boundary of the deep-water oxygen concentration range thereby rises from 2000 to 1300 m; this boundary marks the upper boundary of the Arctic Intermediate water. Core depths of Arctic Intermediate and of Iceland-Scotland overflow water, are derived from the potential-temperature/salinity diagrams obtained in the western basin, and are extended to the other stations by assuming lateral spreading to occur along isopycnal surfaces. The core depths for the Intermediate water obtained in this manner, are supported also by the potential-temperature to silicate relations. The bottom water of the westernmost station of the section, at 44° N, 43° W, is of Denmark Strait origin, and it produces a distinct reversal in the vertical trends of salinity, silicate, phosphate, and oxygen, at 4300 m depth. The concentration of the nuclear-weapon produced nuclide tritium increases within the Denmark Strait water core towards the bottom. Further tritium concentration peaks appear in the intermediate and deep water at this station. At the next Station east on the section at 43° N 34 ° W, tritium concentrations are essetially zero below 2000 m depth, and are distinctly smaller than on the westernmost station, between 600 m and 2000 m depth. This "Meteor" section was track F of the Atlantic network of the international Geochemical Ocean Sections Program (GEOSECS)