A study of the currents of the outer shelf and upper slope from a decade of shipboard ADCP observations in the Middle Atlantic Bight

Since 1992, upper ocean ADCP current data between New York and Bermuda have been gathered from the container ship Oleander to identify long-term changes in the shelf, slope, Gulf Stream and Sargasso Sea. Temperature and surface salinity data have been been collected along this route since 1978 by NOAA/NMFRC. The first ten years of ADCP data from which the effects of warm ring have been removed are used to describe processes within the shelfbreak frontal sub-region. The Eulerian mean velocity structure shows an along-isobath shelfbreak jet with maximum speeds of O(0.15 m s^-1) offshore of which is a ∼30 km wide relatively quiescent region. There is also an offshore slope current 40 to 50 km wide extending vertically to 300 m, with similar velocities as those found in the shelfbreak jet. The mean shelfbreak jet transport is 0.4 Sv while the slope current adds another 2.5 Sv. Maximum shelfbreak transport occurs in the fall and winter while the slope current reaches its maximum during the spring. In stream coordinates, the shelfbreak jet has maximum speeds of 0.35 m s^-1, a width of ∼30 km and a vertical decay scale of ∼50 in. The maximum Rossby number within the jet, defined by dU/dy _max/f, is about 0.2. Significant interannual fluctuations occur in upper ocean temperature, salinity and currents, some of which appear related to changes in the NAO index. Seasonal changes in the slope current appear to be related to seasonal changes in the wind stress curl over the slope sea.