LONG-TERM CHANGES OF THE ANNUAL CYCLES OF METEOROLOGICAL, HYDROGRAPHIC, NUTRIENT AND PHYTOPLANKTON TIME-SERIES AT HELGOLAND AND AT LV ELBE 1 IN THE GERMAN BIGHT

Long-term series of meteorological standard observations at LV ELBE 1, together with those of temperature, salinity, plant nutrients and phytoplankton biomass at Helgoland Reede in the German Bight, are investigated with respect to the changes of the annual cycles during the 23 years from 1962 to 1984. Most meteorological and oceanographic parameters exhibit unchanged annual cycles within natural variability, except for the air and sea surface temperatures which show an overall increase of about 1°C per 23 years. Conspicuous changes in the annual cycles are observed for the nutrients phosphate, nitrate, nitrite (all strongly increasing) and silicate (decreasing). Phytoplankton biomass increased as a result of the extreme increase of flagellates, although diatoms decreased slightly. This and the shifting and shortening of the nutrient depletion phases are indicative of a strong change in the ecosystem. The changes seem mainly to be because of anthropogenic eutrophication, over-riding possible influences of large-scale climatic changes. © 1990.