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The CTD takes a picture of the water column under Tara

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The CTD takes a picture of the water column under Tara

The CTD takes a picture of the water column under Tara

As you know, Tara acts as a scientific platform for the European Damocles scientific programme. The CTD (conductivity, temperature, depth) is one the main instruments onboard Tara.

The CTD takes a photo of the water column just below the boat at a given moment. More precisely, it records water temperature and its salinity according to its depth.

A bathysounder is lowered with a winch to the bottom of the ocean. Since the beginning of the new campaign that started on 27th of September, twenty-seven profiles have been accomplished to this day. Between 300 and 3500 meters. 55 km worth of cables have been unrolled in the ocean since this date.

What is the data providing in one month and a half?
In its surroundings, the CTD records exactly the depth of water layers, for instance.
Presently, the surface layer is between 0 and minus 40 meters and has a temperature of -1,8°C. This water is relatively fresh.

Between -200 and -400 meters, a second layer is characteristic; it is called the Atlantic layer. It is much saltier with positive temperatures, +1,5°C.
Finally, between 400 meters and the Ocean bottom, a layer of deep water with equivalent salinity and negative temperatures: -0,6°C. This structure is typical of the Arctic Ocean. The brutal variations of this data mark the limits of sub marine frontiers that the scientists call thermocline for temperature and halocline for salinity. 

The advantage of the CTD is that it allows checking on the composition of this structure that varies according to several parameters. The place of collection first and climate regimes evolution afterwards.
One can check for instance thanks to the CTD that the Atlantic layer thickens  as one gets closer to this ocean.

But the CTD also opens new doors. By the quantity of collected data, it enables to fine-tune the knowledge where satellites cannot see anything. Few boats drift on the Arctic Ocean as the Tara does, the data recovered on the surface is thus very important.

Tara 2006-2007

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