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

Abstract

[1] 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 À1 ) 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 À1, a width of $30 km and a vertical decay scale of $50 m. The maximum Rossby number within the jet, defined by jdU/dyj 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.

Seasonal and interannual variability of physical and biological dynamics at the shelfbreak front of the Middle Atlantic Bight: nutrient supply mechanisms

“…Finally, the source minus sink (SmS) shows opposite tendencies between the upper (negative) and lower (positive) part of the water column. Consistent with earlier studies (e.g., Hopkinson, 1987;Fennel et al, 2006), these patterns suggest nutrients are being utilized by phytoplankton near the surface, and are being regenerated at depth.…”

“…For boundary temperature, salinity, and baroclinic velocity, an Orlanski-type radiation condition (Marchesiello et al, 2001) is applied. Surface momentum and buoyancy forcing comes from a standard bulk flux calculation (Fairall et al, 2003) using the NOAA NCEP North American Regional Reanalysis (NARR) archive that includes air temperature, relative humidity, air pressure, short wave radiation, long wave radiation, cloud coverage, precipitation and surface wind speed. We applied the method of Mellor and Yamada (1982) to compute vertical turbulent mixing, as well as the quadratic drag formulation for the bottom friction specification.…”

Variability in the North Atlantic Deep Western Boundary Current : upstream causes and downstream effects as observed at Line W

“…Modeling studies suggest that changes in the Meridional Overturning Circulation (MOC) are related to the rate of production of LSW (e.g. Mauritzen and Häkkinen (1999), Bailey et al part of the water column has very similar speeds to those found in the DWBC underneath it (Flagg et al (2006)). Underneath the Slope Water, the uppermost layer of the DWBC, extending from 500m to 1000m approximately, is occupied by upper Labrador Sea Water (uLSW).…”

Wavenumber Spectrum in the Gulf Stream from Shipboard ADCP Observations and Comparison with Altimetry Measurements

“…In this study, 10 years (1994 -2004) The Oleander observations have previously been used to study interannual variations of the Gulf Stream surface transport (Rossby et al, 2005), seasonal variations of the shelf/slope jet in Middle Atlantic Bight (Flagg et al, 2006), and Gulf Stream warm-core rings (Wei et al, 2008). In this study we focus on the open ocean to be compatible with altimetry measurements.…”