Chemical changes and primary production in upwelled water off Northwest Africa

• Published in: Deutsche Hydrographische Zeitschrift 1980-09, Vol.33 (5), p.192-198
• Main Author: Weichart, Günter
• Format: Article
• Language: English
• Subjects: Marine
• ISSN: 0012-0308; 1616-7228
• DOI: 10.1007/BF02226320

A grid of stations in the sea area off Nouakchott is used for the study of temporal changes in upwelled water after this water has reached the surface. In order to exclude waters which do not belong to the upwelling system of the investigated area, only stations with nearly the same salinity in the surface layer (10 m depth) as was found in the fresh upwelling water are considered. The chemical data of the surface layer are plotted against the corresponding temperatures. The daily increase of temperature in the mixed surface layer of the upwelled water provides the connection between the temperature scale and the desired time scale. The changes of the chemical variables with time are discussed. They look quite similar to the changes which were observed in the open North Sea during the first phase of a spring phytoplankton bloom. From the slopes of the pH, nitrate + nitrite, and phosphate regression lines the net primary production is computed. The result stands in fair agreement with the data published in the literature and with SUP-14 C experiments in the same area. Under the conditions chosen, the chemical changes in the upwelled water at the surface seem to be governed much more by primary (and secondary) production than by vertical and horizontal mixing with the underlying and surrounding waters.