Using the experimental
column allowed sample collection of water and gas at levels where priming of the
auto-siphon mechanisn was possible, that is to say below a depth of 270 metres.
analysis of the CO2 and CH4 content was done in situ, at the exit of the small
separator. The figures obtained by means of the Ga2000 infra-red analyser are
exact and reproducible.
We have added
the respective contents in CO2 and CH4 in the gas taken from different depths
between 270 and 400 m to the figure. One can note a small but absolutely crucial
diminution in methane content as depth increases. The difference in methane content
between the layer at 270 m (27% CH4, 73% CO2) and the layer at 400 m (20.5% CH4,
79.5% CO2) is of 7%.
In the rate of content of gas concentration one can
again remark the existence of those homogenous layers mentioned previously (notably
the 280 - 300 m layer and the 330 - 355 m layer).