The North Atlantic current and its associated hydrographic structure above and eastwards of the mid-atlantic ridge

Abstract

Based on CTD data sets obtained in 1981–1984, XBT profiles, and long-term current meter moorings, the large-scale circulation field of the northeastern Atlantic north of the Azores was investigated. The mean volume transport through a standard meridional CTD section between 40°N and 52°N along the eastern flank of the Mid-Atlantic Ridge (MAR) was estimated to be 30 ± 9 Sv, with the North Atlantic Current (NAC) transporting 26 Sv. The NAC was found to be composed of clearly defined current branches (jets), that appear in temperature-salinity diagrams as a modal structure of the Central Water. Whereas the northernmost current branch (subarctic front) was found to be topographically fixed at the Gibbs Fracture Zone, the number, intensity and T- S structure of the remaining current branches, as well as their path over the MAR, are subject to intense variability. From 2 years of observations the branches were found to continue into the basins east of the MAR. They appeared as mesoscale features in a region of increased eddy kinetic energy and are interpreted to result from baroclinic instability. No indications of a branch of the NAC moving south, i.e. a recirculation as part of the North Atlantic subtropical gyre, were found.