flume, and the flow field in the flume nozzle determined by 

 moving it relative to the skin sensor. The u field with a flow 

 of 22.9 1/min is shown in Figure 2. The subsequent field- 

 deployable flume nozzles were built using Plexiglas, with 

 vertically extended sidewalls to penetrate into the sediment. 



The resuspended fluff layer material flows through six holes 

 at the end of the flume and is withdrawn to flow through a filter 

 assembly. There are two configurations for this "downstream" 

 pumping filtering assembly. 



The configuration for the Johnson Sea-Link mounts the flume 

 on its hydraulic arm, and utilizes its pump capability, operated 

 by the hydraulic system, and a filter holder assembly designed by 

 Dr. D. Long (Michigan State University). The pump is located 

 downstream of the filter holder, with a flow meter to provide the 

 cockpit crew with instantaneous flow rate and accumulated flow 

 information. The filter holders, constructed of aluminum, hold 

 filters of 19.8 cm diameter, and are placed in a bucket mounted 

 on the sub's lazy susan array. At the time of this writing, the 

 sub has the capability for only one filter usage per dive. While 

 the lazy susan array normally allows for multiple bucket usage, 

 the weight of the filter holder prevents the normal tight fit 

 between the upper edge of the bucket and the top plate overlaying 

 the buckets, which is necessary to ensure that (1) pumped water 

 does not leak out of the bucket before going through the filter, 

 and ( 2 ) entrainment of outside water occurs into the slurry 

 containing the fluff material. A filter placed into another 

 bucket for the duration of a dive serves as a control for 

 processes such as adsorption of dissolved organic matter onto the 

 filter. We use Schleicher and Schuell No. 30 glass fiber 

 filters, which have acceptable flow rate and an effective pore 

 size of several micrometers. 



The Delta submersible does not provide pumping and 

 filtration capability, and thus requires a completely self- 

 contained unit. Accordingly, we have built a lander device 

 containing all of these functions, which can be deployed by 

 either submersible or SCUBA divers (Figure 3). This device 

 consists of a housing containing power supply, motor, pump and 

 control circuitry carried on two skids, between which is mounted 

 the sampling flume. The housing was fabricated from 6061 (T6) 

 aluminum pipe, 36" long x 8" dia. x 0.375" wall thickness, with 

 3/4" end plates, welded at one end, flanged, 0-ringed and bolted 

 at the other, with the entire assembly anodized. Inside the 

 house a 24 volt battery pack (12 sealed, starved electrolyte 

 cells) is contained inside a separate gas-tight aluminum housing. 

 The batteries are connected, through a magnetically activated 

 reed switch attached to the inside wall of the housing, to a 24 

 volt, 5 amp, 3600 rpm motor. This motor drives through a 

 specially-designed magnetic coupling to a nylon centrifugal pump 

 mounted on the outside of the flanged end wall of the housing. 



The pump was operated by holding a magnet next to a target 



219 



