September 1998 had one of the lowest amount of sunshine hours since the beginning of regular weather data measuring. The month's mean temperature of 14 °C coincided with the long term mean temperature. The air temperature was clearly below average. October was the wettest in this century's history.
While the mean surface temperature in September was higher than the long term month average (1971 - 93) at 14.0 °C, the month of October was normal (mean temperature 12.0 °C), and November was too cold (mean temperature: 9.3 °C).
A wide variety of diatoms, flagellates and ciliates was observed along the Lower Saxony coast. Potential toxic Dinophysis were counted with 200 individuals/Liter at only one station (Jade). In October and in November, the concentration of the phytoplankton decreased with the falling water temperature. Dinophysis were found in the Harle (100 Ind./L) in the beginning of October and in the Ems (100 Ind./L) in the second half of October. At the end of October and the beginning of November, the Odontella sinensis levels increased from many to numerous. With winterly water temperatures in November, species that prefer cold temperatures appeared in greater numbers.
At the end of October, the bulkcarrier MS PALLAS stranded near Amrum. About 50 tons of Diesel oil and heavy fuel oil spread into the Wadden Sea. The total number of birds terminally affected by the oil pollution was estimated at 10800.
At the network station LT Kiel, the surface temperature in September was 14.7 °C below the value of the last year. Mid-October the temperature was 11.4 °C, lower than the previous October, and the last part of October was 9.6 °C, higher than the previous year. In November, the cold weather
led to a greater cooling of the water column to 4.5 °C. Hydrogen Sulphide was measured in Bornholm Basin, Gdánsk Deep, in the Faroe Deep and in the Gotland Deep. At the measuring station Seebrücke Heiligendamm, many different species of developing dinoflagellates were observed from August through September. In October, the phytoplankton biomass was low. In the south Baltic Sea centric diatoms and dinoflagellates
were dominating the phytoplankton from the end of September to the beginning of November. In the plankton of the Bodden of Rügen blue-green algae continued to dominate the rare algae community.