Seasonal stratification in the northwest European shelf seas

Abstract

The seasonal stratification in the northwest European shelf seas has been studied using a two-layered thermal model combined with an observational database. The model, which includes the effects of surface heating, wind mixing and tidal stirring, was run with a 1 day time step to reproduce the seasonal cycle of the temperature structure of the shelf seas. The computed temperatures were then compared with a temperature database, derived from 45,000 XBT profiles, and showed an agreement of better than 1°C for most regions of the shelf. The predictions were less accurate in parts of the northern North Sea where the stratification is linear with depth and the two-layer model represents a poor approximation to the thermal structure. The effects of anomalous seasons, e.g. a severe winter, were modelled and estimates made of the persistence of such events on the thermal structure during subsequent months. The results suggest that anomalous seasons can effect water temperatures for time scales of the order of 1 year. The method of inverse analysis was applied to the heat balance of the shelf seas and seasonal patterns of the residual circulation were determined. The winter circulation pattern, in particular, was in good agreement with estimates derived from observation and wind-driven models.