There are many challenges to working in the deep-sea vent environment, which require specialized sampling equipment. For example, samplers must be designed to withstand pressures < 200 times those we live under, temperatures up to 400°C (752F), and fluids that dissolve metals in < 1 day. In addition, because some of the most valuable measurements are of chemicals and gases that occur in extremely small amounts, it is also important that the instruments remain free from anything that may contaminate the samples. Because of these constraints, one of the most common materials used in the design of equipment to sample vent fluids is the metal called titanium.
During this expedition, we will use two specially designed pieces of equipment to sample Lost City hydrothermal vent fluids for chemistry.
The first kinds of instruments are titanium Major Samplers. These discrete water samplers use a syringe like plunger to draw in vent fluids through a narrow titanium nozzle that is placed down into the throat of the vent. Each sampler draws in 760 ml of vent fluid. These samplers are used to obtain fluids suitable for chemical analyses of major and trace elements in the fluids and some isotopes.
The second sampler called the
Hydrothermal Fluid Particulate Sampler, is much more complex, and it will be a major work-horse for this cruise will be the HFPS because it is especially useful for sampling diffusely flowing fluids and for obtaining particulate samples of microbes that may be entrained in the vent fluids. This sampler was built by NOAA-PMEL and is operated by David Butterfield. The HFPS allows up to 14 water samples plus 10 filters to be obtained on a single dive. Check valves prevent loss of sample back to the main fluid line, and pressure relief valves allow some sample expansion during decompression. An electronic control package allows the user to control both pumps and the valve, and to display and collect temperature and flow-rate/volume data using a graphical interface on a PC.
In concert, analyses of these fluids are critical to understanding the rock-fluid interactions that occur deep within the Atlantis Massif. They will help constrain the temperatures that the rocks are altered at, and fluid-mineral precipitation reactions that occur within the 200 foot tall chimneys. Their chemistry may also record the influence of microbial populations on the compositions of the fluids and they may inform us on the compositions of fluids during formation of the early Earth.
