Logbook: August 6

Gas Sampling at Hot Vents

47°56.95'N / 129°5.88'W

Gas Tight processing equipment aboard the Atlantis. (click image for larger view)

NeMO 2007 includes samples collected directly from hydrothermal vents using titanium Gas Tight Bottles. On board Atlantis, the samples are processed to extract their gaseous contents. Each sample's liquid and gas is expanded into portions and sealed for later chemical analysis on land. This work is done by NOAA Vents Program's helium isotope mass spectrometry laboratory and the University of Washington's oceanographic chromatography lab.

The Gas Tight Bottles are capable of maintaining a vacuum as well as surviving high pressures. The bottles are sent to the depths of the ocean without any air. Making a good seal is very important to maintain the ratio of helium-3 to helium-4 in the sample. This ratio is one of the more important quantities measured. Helium-3 concentrations are seen as a measure of magmatic input to a vent system. Perturbances of its ratio to heat have been identified as a result of a seismic event with magmatic movement. Different volcanoes will have different isotopic ratios and different ratios of helium-3 to carbon dioxide. Sufficient concentrations of hydrogen and methane gas also indicate the gas reaction chemistry below the ocean floor.

During dives, Gas Tight Bottles are opened only when their intake is in the flow of vent. At the end of Jason dive, they are brought to the surface and attached to an analytical vacuum system which removes any air between the Gas Tight intake and vacuum. The vacuum system then separates the sample into different components. The proper sequence of expanding and contracting of bellows, and opening and closing of the valves, collects the gas for quantification.