Frontal systems in the German Bight and their physical and biological effects

Abstract Results of an interdisciplinary study on fronts in the German Bight are presented. During normal summer conditions a frontal system is a permanent feature north of the East Frisian Islands. It separates well mixed coastal water from stratified North Sea water. In the transition zone one observes a cold salty belt with a front towards the well mixed and a separate front towards the stratified regime. Fronts of the river plume type occur in the eastern part of the bight. Upwelling water in the region of the old Elbe Valley near Helgoland is separated from surrounding water by well developed fronts. Physical observations are discussed together with biological implications as accumulation of organisms and the role of fronts for the distribution of zoo- and phyto-plankton communities. It is shown that strong fronts are not necessarily associated with high biomass accumulation. In a case study an intensive phytoplankton bloom is traced back to small horizontal inhomogeneities in the surface layer.