The first part of the C-SWOT campaign is dedicated to measurements in the Cassidaigne submarine canyon, located in the Gulf of Lion, Northwestern Mediterranean Sea, 7 km off Marseilles.
By Lénaïg Brun
Presentation of the Cassidaigne canyon
The Cassidaigne submarine canyon is located in a very active circulation area. First, the water masses are forced by strong westerly (Mistral) or easterly wind events which may generate upwelling or downwelling processes in the canyon. Second, the Northern Current, the main circulation in the Northwestern Mediterranean Sea, flows over the Gulf of Lion off the coast. Under specific events such as southeasterly storms, a branch of this current may enter the Gulf of Lion and interact with the Cassidaigne canyon. Finally, the morphology of this canyon differs from the other canyon in the Gulf of Lion. It is 15 km length and 6 km wide. Its gorge is characterized by a bottleneck of 2 km wide.
Why studying the Cassidaigne canyon?
The Cassidaigne canyon constitutes an interesting area to study from various point of views:
- It is a dynamical region favoring exchanges of water masses, nutrients, temperature, sediments and even pollutants such as microplastics form the surface to the deep sea and inversely.
- The bottom of the canyon is sediment-rich whose transport depend on the canyon dynamics.
- It hosts a large variety of marine ecosystems such as cold-water corals.
How do we study the Cassidaigne canyon?
To identify and analyze the hydrodynamic processes at play in the Cassidaigne canyon, it is necessary to gather data on the current direction and intensity at different locations in the canyon. To do so, 5 ADCP (Acoustic Doppler Current Profiler) moorings are placed along the canyon axis at various depths. They will be placed in the canyon for one year to gather a maximum of data on the hydrodynamic processes at play, depending on the season.
How does it work?
An ADCP is a measurement device allowing to calculate the current direction and intensity in the water column. It emits a signal across the water column through 4 beams oriented perpendicularly to the flow. When the signal meets an obstacle or a particle (whose movement correlates with the movement of the flow), it is reflected back to the ADCP, thus giving an information on the flow.