The ISCA is the chemical outgrowth of vent fluid temperature 

 and flow monitoring instrumentation first deployed by researchers 

 from the University of Washington during a 1984 Alvin dive program 

 (MERGE Group, 1984). The design of the ISCA draws heavily upon 

 the relatively new technology of flow injection analysis (FIA) and 

 the pioneering work of Johnson et al. (1986b) who made in situ 

 chemical measurements from Alvin with a SCANNER. A block diagram 

 of the ISCA is shown in Figure 8. The instrument is capable of 

 determining solutes that can be measured by colorimetric detection 

 at wavelengths in the range 550-900 nm. It consists of a 

 peristaltic pumping system that propels sample (or standard) and 

 reagent streams through a reactor manifold and a simple 

 photometric detector consisting of a light-emitting diode and 

 phototransistor. These components are subjected to in situ 

 pressures, with electrical components (motors and solenoids) 

 isolated in fluid-filled, pressure-compensating housings. 

 Controlling electronics and battery supplies are contained in a 

 pressure case. The controlling electronics are built around a low 

 power data logger with 28K of user partitioned memory, an on-board 

 BASIC operating system and an RS-232 interface. All of the 

 components are contained within an aluminum frame, 18" x 18" x 

 26." Chemical modules were built to determine H4Si04, H2S, Fe^ + , 

 Fe^ + and pH. Two or three of these can be used at once. 

 Temperature is also monitored (by thermistor) with a 0.1°C 

 resolution. The system can be used in two modes. The monitor 

 mode involves measuring fluids periodically over several days 

 under computer control, deploying and recovering the system with 

 Alvin . The scanning mode involves analyzing fluids during the 

 course of an Alvin dive, with the system controlled via an RS- 

 232 link into the submersible. 



The system was configured to determine H2S, Fe2 + , pH and 

 temperature during a 3-day deployment at a low-temperature vent at 

 the ASHES site (Fig. 1). The data recorded indicate that the 

 motor driving the pump was running erratically and eventually 

 stopped. While this failure was disappointing, the test had many 

 positive aspects. Sufficient data was obtained to determine that 

 all other components worked as expected. Alvin had no problem in 

 deploying or recovering the instrument. Several ways of improving 

 the design were identified. We are confident that the problem 

 with the motor will be resolved and look forward to our next 

 opportunity for deployment and to extension of the time span for 

 in situ chemical monitoring. 



In conclusion, we have presented the preliminary results of 

 our ongoing studies to understand the submarine hydrothermal 

 venting system at the ASHES site on Axial Volcano and its 

 contribution to the integrated venting source strength of the Juan 

 de Fuca ridgecrest. The vent fluid data for this site are unique 

 with respect to the low CI values encountered at a single 

 anomalous vent within a small vent field. The likelihood that 

 phase separation is responsible for the anomalous vent fluid 



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