Azti-Tecnalia explores for the first time the inside of ocean eddies located off the Basque-Cantabrian coast
This small submarine was off the Basque-Cantabrian coast between the end of July and end of September measuring salinity, temperature, dissolved oxygen, chlorophyll content and water turbidity. The data gathered will provide Azti-Tecnalia experts with greater knowledge about this type of oceanic structures and the effect they may exert on the marine ecosystem, mainly on the eggs and larvae of the species that spawn in the area. The eddies in the Bay of Biscay had so far been studied by means of satellite imagery, oceanographic models and drifting buoys. What is new about the Azti-Tecnalia campaign lies in the in situ, three-dimensional observation of the eddy by means of the Glider submarine vehicle, which moves vertically in the waters following a zigzag immersion/emersion. During the mission, when the oceanographic vehicle reached the surface, it sent all the gathered information back to the R&D centre via satellite. That way it was possible to observe that these eddies significantly modify the depth of the seasonal thermocline, as well as chlorophyll concentration and water turbidity. However, despite knowing that they have a depth of over 1,000 metres, the researchers are unable yet to determine their total vertical extension exactly, nor where they originate. To complement Glider’s measurements, during the so-called GESEBB campaign wo drifting buoys were deployed on the centres of the eddies in order to calculate their turning speeds and to study their retention capacity. All this information will enable experts to determine how these eddies affect the marine species inhabiting pelagic waters –the ones closest to the surface–. Scientists reckon that eddies could affect the marine ecology in the area firstly due to their role on the marine dynamics, and secondly, due to their capacity to retain plankton, as for example eggs and larvae of various fish species that spawn close to the sampled area. The research will also make it possible to find out the effect of these eddies on the structure of the water column. Depending on their rotation sense, they cause the surfacing of deep water. Deep water masses tend to have a high nutrient concentration, and when they surface to depths where solar energy allows photosynthesis to take place, it encourages the production of primary organic matter. Ocean eddies are the marine equivalent of atmospheric areas of low and high pressure. They can modify the general oceanic circulation of the area, and transport heat, particles and biogeochemical properties from their origin area. So the eddies produced in coastal areas, which later drift to open ocean may carry contaminants, nutrients, larvae of different species, etc. The studied eddies do not pose any hazard for shipping since they rotate weakly and they , are geographically located from the coast as far as 45ºN and between 2º30’W and 4º30’W. These oceanic structures are produced over the winter and last several months. They routinely migrate westwards although depending on the ocean conditions, some years stationary eddies may form and remain off our coasts for months. Azti-Tecnalia’s research campaign has European Union funding through the JERICO project of the 7th Framework Programme, and from the Department for Economic Development and Competitiveness of the Government of the Basque Autonomous Community (region). The Basque Autonomous Community Government’s Directorate for Emergency Response and Meteorology of the Department of Security, the Spanish Maritime Safety Agency –SASEMAR, and the National Institute for Sciences of the Universe-INSU/CNRS (France) are collaborating on this initiative.
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