Brazil Basin Tracer Release Experiment (BBTRE)- Year 2
When we reached the tracer injection area in March, 1997, fourteen months
had passed since 114 Kg of tracer was deployed at 4000 meters depth along
the flanks of the Mid Atlantic Ridge. The primary purpose of the second
trip to the area was to sample the tracer patch and map its dispersion
over time. The HRP was used to make instantaneous estimates of turbulence
and vertical dispersion at the sites
CTD stations and bottle samples were taken. The only HRP dives that don't
have associated CTD and bottle data are those for an excursion on to the
crest of the Mid-Atlantic Ridge comprised of dives 29-40. By the end of
the cruise, within the accuracy of the sampling methods, all of the tracer
injected had been accounted for.
The other goal of the experiment was to augment the measurements made
on the previous cruise to obtain a more complete
cross-basin section. The additional diffusivity estimates over the
Mid Atlantic Ridge show even higher levels of mixing than were observed
the previous year. The estimates of mixing based on the tracer
dispersion generally agreed with the levels of mixing obtained from the
HRP data, and were much higher than obtained in the NATRE project (by two
orders of magnitude!)
Publications resulting from this experiment are:
Polzin, K. L., J. M. Toole, J. R. Ledwell and R. W. Schmitt, 1997. Spatial
variability of turbulent mixing in the abyssal ocean. Science, Vol.
Montgomery, E. T., 1998. High Resolution Profiler Use in the Brazil Basin
Tracer Release Experiment. Woods Hole Oceanographic Institution Technical
Report, 98-08, 34 pps.
Zhang, J. and R. W. Schmitt, 1999. The impact of salt fingering on
the thermohaline circulation under mixed boundary conditions. Journal
of Physical Oceanography, in press.
Ledwell, J. L., E. T. Montgomery, K. L. Polzin, L. C. St. Laurent, R. W.
Schmitt and J. M. Toole, 2000. Evidence for enhanced mixing over
rough topography in the abyssal ocean. Nature, 403
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