Production primaire au niveau de la thermocline en zone néritique de Méditerranée Nord-Occidentale |
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Authors: | G Cahet M Fiala G Jacques M Panouse |
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Institution: | 1. Laboratoire Arago, Banyuls-sur-Mer, France
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Abstract: | Vertical profiles of physical, chemical and phytoplanktonic parameters are described, at the level of the thermocline, in the area of Banyuls-sur-Mer, France. The results show that the thermocline divides two masses of water: (1) Mediterranean surface water with low nutrient concentrations and a salinity below 38.00 ‰; (2) deep, nutrient-rich upwelled water (N?NO3 >3 μat-g·l-1, P?PO4>0.3 μat-g·l-1, >38.30 ‰ S), which comes from the upper limit of the Mediterranean intermediate water, usually located at the 200 m level. Consequently, conditions are suitable for high production rates at the bottom of the thermocline, where Chl a is above 0.5 mg·m-3; dominant species are Nitzschia delicatissima and N. pungens. A diagram is presented explaining the different effects of the pycnoclines on primary production: eutrophication at the pycnocline levels is the result of passive accumulation of phytoplankton and organic matter during sedimentation, and/or of reduced diffusion of nutrients from deep waters towards the surface. |
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