buoyant and smokeless plumes. Shimmering water (low temperature 

 discharge) is associated with patches of tube worms located 

 throughout the high- temperature sector and is also ubiquitous 

 about the bases and sides of the sulfide structures. 



METHODS 



Pisces-IV 



The vent fluid data reported here were determined from samples 

 collected during a joint Canadian-U. S. sponsored series of 15 

 dives on Axial Volcano conducted during July-August 1986 using 

 the Research Submersible Pisces IV and tender ship Pandora II. 

 Submersible navigation was performed relative to an acoustic 

 transponder net. Vent water temperatures were initially deter- 

 mined by commercially available platinum resistance thermometers. 

 After three of these mechanically failed during immersion in high- 

 temperature vent fluids, an impromptu thermo-couple system was 

 fabricated from a thermal sensor borrowed from the propulsion 

 system of the Pandora II. Temperatures were not measured 

 coincidently with the collection of vent fluids: typically, the 

 spatial location of maximum temperature sensor output was 

 memorized by the submersible pilot during a thermal search of the 

 vent fluid flowstream after which the temperature probe was 

 returned to its holster, the sampler of choice was picked up by 

 the manipulator arm, and its snorkel maneuvered into position for 

 sampling. Venting fluids were collected in paired 755 mL titanium 

 syringes (Major Samplers) described by Von Damm et al. (1985) 

 which were available to us courtesy of the Alvin Group, WHOI . One 

 sample was collected explicitly for vent fluid gases in a UCSB 

 Gas-Tight Bottle designed by J.E. Lupton. Because of space and 

 loading constraints on Pisces , only a single titanium sampler 

 pair was filled during any given dive. Additional water samples 

 were collected in selectable plastic reservoirs indexed upon 

 demand into the flowstream of the Pisces slurp gun. 



Determinations of vent fluid alkalinity and pH were performed 

 shipboard. The methods, precisions and laboratories associated 

 with these as well as the shore based determinations of ^He, Mg 2+ , 

 H 4 Si0 4 , H 2 S, CI", Ca 2+ , Mn 2+ , and Fe 2+ are given in Table 1. 



Alvin 



A second series of 11 dives at the ASHES vent field was 

 conducted using Alvin/Atlantis II during September-October 1987. 

 The chemical data for 27 water and 11 gas samples collected during 

 this expedition are presently being determined and will be 

 reported elsewhere. Temperatures were measured at each of the 

 high-temperature vents at ASHES using a platinum resistance 

 thermometer which was an integral part of a combined sampling and 

 sensing system for vent fluids that will be discussed later in 

 this report. Drift in the calibration of this system was 



37 



