MODELING WATER COLUMN PROCESSES IN THE NORTH-SEA

In the North Sea advective transports are not negligible. Nevertheless , physical properties like sea surface temperature (SST) can be hindca sted with sufficient precision by vertical process water column models . Annual cycles Of SST in the southern, central, and northern North Se a can be simulated using physical upper layer models with relatively s mall RMs errors. For the Fladenground Experiment (FLEX'76) in the nort hern North Sea the RMS error is less 0.3-degrees-C for the 2 months of the experiment. This justifies the initial use, at least, of vertical process water column models in simulations for investigating transfer processes in the planktonic ecosystem. Experiments have shown that th e simulated entrainment velocities at the bottom of the mixed layer du ring summer are critically dependent on the resolution of the forcing variables. The effects of this resolution on the annual phytoplankton dynamics will be discussed. Phytoplankton dynamics are strongly influe nced by those of the zooplankton, and vice versa. Several field invest igations have shown that, seemingly, phytoplankton cannot sustain the observed stock of zooplankton in the northern North Sea: there exists a gap between the abundance of phytoplankton and the need for it to ma intain the zooplankton. Revisiting FLEX'76, the simulations with water column models of increasing complexity concerning detritus suggest th at pelagic detritus can fill the gap in food availability for the zoop lankton. If it is assumed that the zooplankton feeds also on detritus, the zooplankton experiences no food shortage.