Smoothseafloor During the campaign, a treasure hunt of a kind somewhat unusual has mobilized some of us. This was to identify and locate on the bottom of the sea of signs of current activity hydrothermal. Such activity is often characterized by an emission, on the ocean floor, fluids that differ sharply from the surrounding seawater at temperatures and concentrations of metals and methane often much higher. In hydrothermal areas, such fluids resulting from the processing of seawater that has seeped through cracks in the oceanic crust to great depths and gradually warmed and enriched in metals and methane in contact rocks it has helped transform one another.
For this, explored the depths, fins, mask and snorkel no longer sufficient. Players use a CTD or CTD (Conductivity, Temperature, Depth) the name of the sensors installed on that instrument in its simplest configuration. This device suspended from a cable electrocarrier (left) for transmitting data is continuously lowered from the surface to the seabed at a speed of about 1 meter per second. During the descent, traders scrutinize carefully (photo middle left) to screen the profiles (that is to say, the evolution with depth) measurements delivered in real time by the sensors (temperature, conductivity and turbidity particular). The sensitivity and accuracy of the sensors can detect small abnormal variations in the patterns. In open ocean environment, that is to say far from shore, these anomalies may correspond with high probability events of hydrothermal activity. To confirm this, the sea water located at the depth of the anomaly is then removed through special bottles installed on the device and whose closure is triggered on demand by scientists.
Once the CTD back on board, sampling (see photo middle right) are made for assays of methane and dissolved manganese (pictured right) made either on board or ashore to return campaign. The identification of concentrations greater than that corresponding to the average composition of sea water reveals the presence of more or less near a hydrothermal vent. The operation is then repeated as many times as necessary to identify the best area to locate precisely the issue responsibly. But it is better to be lucky or otherwise dispose of a lot of time and patience because the underwater currents can transport indices over long distances and in unexpected directions and the game is a bit like finding a needle in a haystack.
Often scientists need to give up before reaching their goal. This is for another time or for another team who can benefit from the information collected.
Between the CPC, the spirit of explorers discovering our leaves, however, not lead them. They lead one second treasure hunt: the best bottles in the cellar of the Marion Dufresne. And then the results are much more sensitive ...
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