Water mass characteristics in the equatorial North Atlantic: A section nominally along 6.5°N, July 2000



[1] In July 2000, a transatlantic conductivity-temperature-depth/hydrographic section was occupied on board the Russian R/V Akademik Ioffe in the northern equatorial region from 9°26′N, 17°22′W to 3°48′N, 47°16′W near the World Ocean Circulation Experiment (WOCE) A06 line. The water mass characteristics and the main features of cross-sectional circulation are reported on the basis of the potential temperature, salinity, potential density, and silicate distributions along the section. A scheme of the upper ocean circulation dominated by the near-surface eastward North Equatorial Countercurrent, most intense at 5.5°–6°N, and the subsurface cyclonic flow of the North Equatorial Undercurrent, is presented. The boundary flows along the Brazilian slope are revealed at the Upper and Lower North Atlantic Deep Water (NADW) levels, while the main pathways of intermediate waters and the Middle NADW are offshore. The northward recirculation of NADW is observed in both the western and eastern basins; in particular, a reversal of the Deep Western Boundary Current at the Middle NADW level is detected. The warming of the intermediate, deep, and near-bottom waters in the interior eastern basin is revealed from comparison of the section temperature data with those obtained at the WOCE A06 line in 1993. The substantial 1993–2000 temperature increase (+0.02°C–0.1°C) at the intermediate and upper deep levels suggests that the previously reported long-term warming above 2500–3000 m in the equatorial and subtropical North Atlantic between the late 1950s and early 1990s continued in the interior eastern equatorial basin during the last decade of the 20th century.