The potential impacts of climate change on the hydrography of the northwest European continental shelf

Changes in global atmospheric conditions have the potential to substantially influence shelf sea environments with far reaching consequences for their ecosystems. Here we focus on the northwest European continental shelf, and review the mechanisms by which climate change might affect the temperature, salinity and stratification of this shelf sea. We explore results from a single pair of Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS) simulations forced by the Hadley Centre regional climate model, for conditions typical of 1961-1990 and 2070-2098, under a 'business as usual' emissions scenario (SRES A1B). This provides a single, physically plausible, representation of the future and a consistent representation of the recent past. Comparing these simulations, the shelf sea regions of this model are shown to warm substantially more than the open-ocean, by between similar to 1.5 and 4 degrees C depending on location. Across the whole domain the surface waters are projected to be similar to 0.2 p.s.u. fresher by the end of the 21st century. The strength of seasonal stratification is shown to increase by similar to 20% on the shelf, compared with 20-50% in the open-ocean. The former being controlled by temperature and the latter by salinity. In shelf seas away from the direct influence of river discharge, stratification is projected to start similar to 5 days earlier and breakdown similar to 5-10 days later each year, hence extending the stratified period. An ERA-40 re-analysis forced simulation provides a reference, along with validation from gridded monthly mean data from the ICES data base