Shearmeter

Brazil Basin Tracer Release Experiment Shearmeters

Tim Duda, John Toole, Jim Ledwell
Woods Hole Oceanographic Institution
Woods Hole MA 02543

Dr. James Ledwell and colleagues ease the first

Shearmeter into the South Atlantic from

the fantail of the RV Seward Johnson,

March 26, 1998.

Brian Guest Photo.

BBTRE Shearmeter Results JPO manuscript

BBTRE Shearmeter Operations Technical Report WHOI-2002-01

Shearmeter home page

Shearmeter Brazil Basin Test Mission webpage

Five shearmeters, shown partially assembled in the image below, were deployed in April 2000 at the site of the sulfur hexafluoride tracer dispersion study in the Brazil Basin. The sulfur hexafluoride study was at approximately 21 degrees south, 17 degrees west. The chemical was injected at approximately 4000 m depth over the rugged mountains sloping up to the Mid Atlantic Ridge which is to the east. Two shearmeters were launched at 4000m depth, two at 3500 m, and one at 3000 m. One was damaged and not deployed.

These shearmeters are the second design to be deployed in the ocean. This version will listen to 260-Hz acoustic sources, allowing their trajectories to be computed. They are made of anodized and painted 7075 high-strength tubing. They are sectional to allow air shipment to the RV Knorr, with three sections of equal length.

The goal of the mission is to collect long time series of shear and gradient Richardson number at the upper edge of the Antarctic Bottom Water, where the tracer dispersion study is being carried out, and in the water above.

One instument surfaced on schedule, 01 Nov. 2000. It floated at 3100 m depth rather than the intended 3500 m. It sank 100 meters over six months at a fixed rate. The compass failed to operate correctly, probably due to extraneous magnetic fields in the instrument, and the rotation counting sytem produced aliased signals which are probably not usable. Two sound sources were heard intermittently so the trajectory can be computed. The compass functions correctly in the damaged and returned instrument and the cause of the rotation problem has not been identified.

The shearmeters were built by Webb Research Corporation.

Instruments being prepared by Brian Guest and Brazilian scientist assistants:
Instruments on deck

Links:

WHOI AOPE Dept.
Coastal and Ocean Fluid Dyn. Lab Webpage
Ocean Acoustics Lab Webpage (My formal affiliation.)
Webb Research Corp.Webpage
NSF

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