RESUSPENSION IN THE KATTEGAT - IMPACT OF VARIATION IN WIND CLIMATE AND FISHERY

The recurrence of various agents of fine sediment resuspension in the Kattegat Sea, notably wind-induced wave action and demersal trawling, and their seasonal variation and long-term trends have been estimated. A comparison between the sediment-water interface and the spatial distribution of theoretical wind/wave impact indicated that the sediment is resuspended by further agents at depths below the permanent halocline between 10 and 20 m depth. The climatic deterioration in 1940-1970 had a significant influence on the recurrence of wind-induced resuspension, although this was mostly limited to a 10-30% shortening of the recurrence period. On the other hand, a quantification of the effect of demersal trawling in the same period suggests a total shortening of recurrence at bottoms below the halocline by 75-85% in the autumn and winter, and with one order of magnitude (90%) in spring and summer, compared with the effect of waves only in the 1930s; resuspension caused by near-bottom uni-directional currents was not quantified. At these deeper bottoms, resuspension conditions have approached those prevailing at shallow bottoms above the halocline. © 1990.