Continuous measurements of hydrographic and hydrochemical parameters in surface waters of the Baltic Sea and the North Sea in march and april 1991

In March/April 1991 hydrographic parameters (salinity, temperature) and hydrochemical parameters (concentrations of phosphate, nitrate, nitrite, ammonia, silicate and pH) were measured continuously in the surface water of the Baltic Sea and the North Sea. The hydrographic parameters were determined by means of a TS,pH probe and the chemical parameters were determined by means of an Auto Analyser. The cruise track through the Baltic Proper, the western Baltic Sea, the transition area to the North Sea and the North Sea with the mouth of the river Elbe was around 2050 nautical miles long and included some 2100 data-points. The different phases of the Baltic Sea's spring diatom bloom were inferred from the different nutrient concentrations measured; a comparison with the hydrographic data revealed that the bloom was largely unconnected to the hydrography. The same situation was encountered in the North Sea except that the spring bloom there had already reached a later phase. In those regions of the Baltic Sea where a plankton bloom had already occurred or was still under way, strong patchiness of the hydrochemical parameters was also observed; it was sometimes possible to relate it to the topography. This patchiness was far less pronounced in the North Sea and in regions of the Baltic Sea where conditions were still wintry. This paper discusses the advantages and possible applications of the method of continuous measurement of hydrochemical parameters across large areas with high temporal and spatial resolution