Fewer Phytoplankton…

On each of these graphs, each dot represents the concentration of chlorophyll, that is to say the concentration of phytoplankton. «We can immediately observe a clear development», explains Anne Goffart. «At the end of the 1970’s there was a “blossoming” of phytoplankton each spring, which was the time when the nutrient-rich layer rose from the bottom of the sea. These last few years, this phenomenon has almost disappeared! And the disappearance is progressive. » How can this decrease in growth be explained? The researchers know that they can eliminate the theory of local causes as the waters are practically free of man-made pollution. If the phytoplankton in the bay of Calvi have disappeared, this means that the result stems from another general source independent of local factors.

As it is the wind that causes the nutrient-rich water to rise toward the surface, Anne Goffart has correlated the data concerning the wind with the concentration of phytoplankton, and more particularly the number of winter days with strong wind and the concentration of chlorophyll. We can thus conclude: during the years where there is a lot of wind in January and February, the phytoplankton develops; conversely during the years when the wind is rare, there is no phytoplankton. And the relation between these factors is very marked. Each time the wind reaches a peak in winter, the nutrients in the water column rise. In other words, the growing shortage of phytoplankton is due to a general climatic reason: the change in the wind system in the bay and along the western coast of Corsica.

This data is of great interest to the other oceanology laboratories, which have not been able to avail of data over such a long period, and are thus incapable of distinguishing some climatic signals from others, particularly those which stem from human activity. «The concentrations in question are indeed very weak. If you are in the vicinity of a water purification plant, which is, for example, discharging water which is a million times richer in nutriments than natural water, it is evident that this will completely obscure those variations due to climate change. The oceanographers are therefore interested in our data in order to use them in mathematical models which would explain what happens in case of modifications in the wind system», continues Anne Goffart.