Gas from the seafloor? Pourquoi pas ?

Beside carbon dioxide, the most important greenhouse gas, methane contributes about 15% to global warming. In order to find out how fast this processes goes on, the methane cycle including sources and sinks has to be better understood. Whereas the terrestrial sources are fairly well known, marine sources are still poorly constrained : What is the fate of methane discharged from coastal sediments, submarine mud volcanoes, hydrothermal vents and gas hydrate fields ? Is it oxidized rapidly by microbes in the water or does it make it to the sea surface and, thus, into the atmosphere ? Against this background it is one aim within the EU project EXOCET/D to improve a state of the art underwater methane sensor which is also highly interesting for the offshore industry.

During the Momareto cruise a German team from the Alfred Wegener Institute for Polar and Marine Research (AWI) and from the small company Franatech / Capsum carries out an "in situ calibration" of the sensors : Victor 6000 allows to use the sensors in combination with the newly developed Pepito water sampler at the methane rich vents of the MoMAR site. Sensor signals can be directly compared to the methane concentration determined by gas chromatography from the Pepito water samples. Since the target area is well investigated all other necessary parameters are known. These optimal conditions are hardly achievable in a laboratory. Thus the scientists are happy to progress with their instrument that exhibits another piece in the mosaic of knowledge.

Methane sensors installed in Victor 6000’s tool sled. They are in line with the newly developed water sampler Pepito allowing a direct comparison of sensor signals and water sample methane measurements.



Uli Hoge, engineer at the AWI, tests the tubings that guide water in line through the sensors into the Pepito sampler.

Jens Gronemann, engineer at Franatech / Capsum, sets up the CH4 sensor array in the lab.

Eberhard Sauter, geochemist at the AWI, appreciates the opportunity to carry out deep-sea tests with Victor 6000.
Technically, it is much easier to bring the sensor to the deep than realizing in situ conditions in a lab (pressure, low temperatures, realistic methane concentrations, exclusion of air bubbles...).


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