A new, automatic hydrothermal fluid sampler using a shape-memory alloy

A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also used to switch the intake valve of the sampler, the intention being to avoid mis-sampling when the inlet in low temperature water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents (1372-1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature was between 138 and 298°C, while the ambient seawater temperature was 3.1 °C. Each prototype collected about 100 ml fluid as designed. The magnesium concentration in the samples indicated a seawater content of 47.5-90.8%, which indicates the entrainment of ambient seawater. Microscopic observation revealed the occurrence of microorganisms in the sample fluids at a population density of 10⁵ to 10⁶ cells ml^-1, which is 2-3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological interest.