Investigation of large-scale circulation patterns in the central North Atlantic: the North Atlantic current, the Azores current, and the Mediterranean Water plume in the area of the Mid-Atlantic Ridge

Abstract

Within the framework of the TOPOGULF experiment, five hydrographic boxes were designed to allow a realistic reference level for geostrophic calculations to be identified. By means of both the inverse method of Wunsch (1978, Reviews of Geophysics and Space Physics, 16, 583–620) and the empirical search method of Fiadeiro and Veronis (1982, Journal of Marine Research, 40, 159–192), geostrophic currents and associated transports across the total length of the Mid-Atlantic Ridge between 24° and 53°N were estimated. As a reference level, an intermediate “level of slow motion” was found in terms of σ 2 = 36.97–37.035 (1500–2900 dbar) to be in good agreement with hydrographic features. The total transport above this level was calculated as 37 Sv to the east. Much of this transport occurs in two principal currents, the Azores Current (12 Sv) and two branches of the North Atlantic Current (17 Sv). A reversion of the total flow in the layer below the reference level was not observed. The meridional extent of the Mediterranean Water outflow was found to be restricted by the Azores Current in the south, and the southern branch of the North Atlantic Current in the north, and the zonal distribution to be influenced by the Mid-Atlantic Ridge. A schematic circulation picture is attempted as a summarized result deduced from this analysis and selected literature.