Cruise Log: July 15, 2008
Sampling Hydrothermal Fluids One of the primary objectives of this expedition is to acquire samples of hydrothermal fluids (hot springs) on the deep sea floor and chemically analyze these fluids in the ship board laboratory. To do this, the team led by Dr. Jeffrey Seewald from the Woods Hole Oceanographic Institution will employ “Isobaric Gas-Tight” (IGT) fluid samplers (‘isobaric’ means ‘constant pressure’). Hydrothermal fluids on the seafloor, in addition to being incredibly hot (over 300°C), are also under the tremendous crushing pressure of the ocean above. Pressures on the seafloor are commonly over 200 times the atmospheric pressure we humans feel at the Earth’s surface. Because of this, compounds like carbon dioxide, hydrogen sulfide and methane, which are normally gases at Earth’s surface, are dissolved in the hydrothermal fluids on the seafloor, just like other common elements such as chloride and sodium. This presented a problem for early researchers attempting to measure the complete range of compounds present in hydrothermal fluids, as early sampling technology was unable to keep these dissolved gases from escaping from the fluids as soon as they were brought onboard the ship. The IGT sampler system is unique in that it keeps the hydrothermal fluid ‘sealed’ under seafloor pressure, trapping the gasses inside, even after the sampler is brought up from the seafloor. The fluid sampler is deployed using Jason’s robotic arm. When a hydrothermal fluid is identified for sampling, the robotic arm grabs the T-handle on the sampler and inserts the “snorkel” attached to the sampler into the path of the hot flowing fluid. A valve attached to the sampler is then opened and hydrothermal fluid rapidly fills the sampler because the initial pressure inside the sampler is much less than the pressure on the seafloor. The sampler is filled when the fluid pressure inside the sampler is equal to the seafloor pressure. At that point, the valve is closed, trapping the fluid and dissolved gasses inside, and the sampler is brought back up to the ship for analyses. |
Dr. Peter Saccocia from Bridgewater State College holds a fluid sampler. The snorkel that is inserted into the path of the hot fluid can be seen extending from the sampler down to the right. |
| When the sampler is ready to be opened back on the ship, small samples of the fluid inside are withdrawn into gas-tight syringes for various analyses, including dissolved gases and other elements. Being able to measure dissolved gases in hydrothermal fluids is crucial to our understanding of subseafloor hydrothermal environments, and compounds such as methane, hydrogen sulfide, and numerous other organic species are also extremely important for microbial ecosystems in and around the vents. | |
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