Exploration for other Lost Cities?- Measuring Gases Onboard the Atlantis

The opportunity to measure gas concentrations at sea can help guide sampling and exploration efforts of the cruise. We will bring a gas chromatograph that will allow measurement of hydrogen (H2) and methane (CH4) on sub-samples of fluid from the various samplers and from samples taken with the CTD in our efforts to explore for similar vent fields. Typically, a small volume of a fluid sample is taken into a plastic syringe (excluding contamination from air) and is then “head-spaced” (helium is added to the syringe) with a volume of very pure helium. This technique promotes the migration of insoluble gas species from the fluid into the bulk gas. Aliquots of the bulk gas are then injected into the chromatograph where the components are separated and quantified. We anticipate H2 and CH4 will be at high concentrations in this system and will serve as good indicators of active hydrothermal venting. By comparing gas concentrations of samples taken at known hydrothermal vents with those taken while exploring with other sensors (CTD), we can ensure that true “hits” were encountered-i.e new sites of venting were discovered. We also hope to take some preliminary looks for the presence of nitrous oxide (N2O) and higher order volatile organics in fluid samples while at sea to aid the microbiologists in their studies of potential microbial processes. We will be determining rates of microbial oxidation of H2 and CH4 by measuring the disappearance of these gases over time in sampled fluids (as compared to sterilized control fluids). The gas chromatograph will allow us to measure the changing concentrations.