Gulf stream and Western boundary undercurrent observations at Cape Hatteras

Abstract

During July 1967 three volume transport measurements of the Gulf Stream were made off Cape Hatteras, North Carolina. The measurements were made using ‘transport floats’, free falling instruments which measure the vertically averaged horizontal velocity and depth. The transport values were 58, 67 and 64 × 10 6m 3/sec; the average transport was 63 × 10 6m 3/sec. The edge of the Gulf Stream for these determinations was defined as the point at which the transport per unit width of the Stream vanished. The transport refers to values normal to a baseline bearing 135°. The velocity measurements indicated that the Gulf Stream extends to the bottom underneath and offshore of the high speed surface layer. A deep southward flow was found on both sides of the deep northward flow. A single hydrographic section was also made across the Gulf Stream. Absolute velocities of the geostrophic currents were determined by forcing the geostrophic transport to agree with the direct transport measurements. An analysis of the temperature-salinity and dissolved oxygen distributions failed to reveal discontinuities between the deep north and South flows. These properties can be related to water properties in the slope water region and Labrador Basin and thus indicate that the southward flowing water is the Western Boundary Undercurrent.