holders are located aft of the manifold. The syringes are 

 actuated by energizing an electric solenoid which releases a 

 compressed spring on the plunger arm. 



The sensor and control lines were passed through the Alvin 

 hull penetration system and connected to a terminal strip inside 

 the sphere. Custom designed interface electronics were installed 

 in the equipment rack, and the data display and logging were 

 performed on a laptop computer with a backlit LCD display. The 

 software, which was written in Forth, displayed an analog plot of 

 the two temperatures, and a digital display of all other 

 parameters. Data was stored on internal floppy discs. 



During operation when the submersible is adjacent to a vent, 

 the pumps are switched on as the pilot removes the nozzle from a 

 holster attached to the basket. As the nozzle is manipulated 

 within the venting fluid flow stream, the observer guides the 

 pilot by watching the display of temperatures on the computer. 

 The data shown in Figure 7 are representative of the real time 

 display. When the highest temperature has been found, time is 

 allowed for the system to come to thermal equilibrium and to allow 

 complete flushing of the system. At the nominal flow rate 

 of 5 liters/min through each pump, this requires approximately 

 1 minute. At this point the pumping rate can be modulated to 

 ensure that the sample is not being diluted with ambient seawater. 

 When equilibrium has been achieved, as exemplified by the manifold 

 temperature reaching a maxima, the pumps are turned off and a 

 sampler is activated. When the nozzle has been removed from the 

 vent, the pumps are again turned on to flush the entire system. 



The system has shown the importance of measuring temperature 

 at the inlet of the sampler. Very small motions of the 

 manipulator arm by the pilot can cause temperature changes of 

 hundreds of degrees and the guidance of the observer is necessary 

 to obtain the highest temperature water at a particular vent. 

 Typically the nozzle is obscured from view during sampling by 

 "black smoke" or resuspended sediments. Relying on visual means 

 to position the sampler in most cases would result in dilution of 

 vent fluids with ambient sea water. 



In Situ Chemical Analyzer (ISCA) 



The 1987 Alvin dive series also provided an opportunity to 

 test a second type of instrument new to the VENTS Program: an In 

 Situ Chemical Analyzer (ISCA) which was designed to determine the 

 chemical output of low-temperature vents over time periods of 

 days. This was conceived to be a first step toward the estab- 

 lishment of an in situ chemical monitoring capability that will 

 eventually provide the information necessary to temporally extend 

 instantaneous plume and vent fluid measurements to time scales 

 appropriate for testing the VENTS Program's ocean basin scale 

 hypothesis. 



49 



