|The deep western boundary current: tracers and velocities|
Rhein, M. (1994). The deep western boundary current: tracers and velocities. Deep-Sea Res., Part 1, Oceanogr. Res. Pap. 41(2): 263-281
In: Deep-Sea Research, Part I. Oceanographic Research Papers. Elsevier: Oxford. ISSN 0967-0637, more
Current meter data; Current velocity; Deep currents; Geostrophic method; Ocean currents; Tracer techniques; Velocity profiles; Water masses; Water mixing; Western boundary currents; Western boundary undercurrents; Marine
In the Deep Western Boundary Current (DWBC) mean velocities obtained by the F11/F12 dating method are far smaller (1-2 cm s−1) than direct velocity measurements (5-20 cm s−1). To resolve this discrepancy, a simple box model is presented that uses the ideas of Pickartet al. (1989, Physical Oceanography, 19, 940-951) to parametrize turbulent diffusion of the current with its surroundings. In contrast to previous models, however, the boundary conditions include all water masses forming the lower part of the DWBC (Denmark Strait Overflow Water, Iceland Scotland Overflow Water and Northeast Atlantic Water). The model-derived mean velocity of the DWBC leads to tracer concentrations that have to fit the observed F11 and F12 distributions, the F11/F12 ratios, and the tritium distributions. Moreover, the model area is extended from south of the Faroe bank along the continental margin of the American continent to 10°S. The model assumes uniform velocity and uniform turbulent mixing along the flow path of the DWBC, and enhanced turbulent mixing in the vicinity of the current compared to the ocean's interior allows the surrounding waters, which remain motionless, to accumulate tracers. The highest mean velocity of the DWBC, which results in model F12, F11, and 3H distributions as well as F11/F12 ratios, compatible to measurements of these tracers along the western boundary, are 4.8 cm s−1. Variations in the composition of the DWBC as well as changes in the time history of the source water masses do not increase the range of the model velocities.