Abstract:
Six drifting floats designed to measure shear were deployed in the vicinity of the Brazil Basin Tracer Release Experiment. The
one-year long time series of oceanographic conditions obtained by the floats are for direct comparison with long-term tracer
dispersion. The purpose of the tracer dispersion experiment was to study mixing of Antarctic Bottom Water at approximately 4000
m depth with less dense water above. Two of the floats returned shear records, one from about 1660 m depth and one from about
2800 m depth. Mean shear at 1660 m was 2.2 x 10 -3 s-1 with N = 1.1 cph, about 1.9 times the Garrett-Munk model amount.
Mean shear at 2800 m was 1.1 x 10-3 with N = 0.5 cph, about 2.2 times Garrett-Munk. There was no apparent depth structure to
the shear recorded by the near-bottom float moving over the mountainous seafloor. The two shear time series and the local tidal
velocities were not strongly correlated, but the tide and shear series did have some similarities. Some variability in the 1660-m
shear may be due to atmospheric forcing. Three floats deeper than 2800 m returned one-year long trajectories. Two trajectories were
persistently eastward.
