Submarine fluid sampling

To collect gas samples a plastic funnel (30 cm diameter) is placed (with a 12 kg ballast around the lower ring) on the gas vent. Then the funnel is connected to a glass flask filled with air at a pressure which is greater than the expected hydrostatic pressure to prevent sea water from entering the sample. This system allows one to change flasks underwater in order to collect multiple samples for each vent. The same device is also used to collect gas samples in NaOH-filled flasks. In this case the external section of the flask valve is filled with distilled water to avoid sea water contamination. A traditional glass sampler, filled with water collected close to the vent, is used for dissolved gas. In regards to hot water sampling from underwater springs, the main difficulty is due to the low water flux. In order to avoid seawater contamination, a evacuated glass flask connected to a steel hose is used. Once the hose is fixed in the spring outlet, a 60 cl syringe connected by a 3 way valve, is used to expel the seawater from the hose and then fill the evacuated flask with only the geothermal water. In this case, seawater contamination is as low as reasonably achievable.

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