Physical Versus Anthropogenic Control of Nutrient Concentrations in the Irish Sea

A three-dimensional, density resolving model (the Proudman Oceanography Laboratory Coastal Ocean Modelling System; POLCOMS) has been applied to the study of long term variability in salinity and nutrient concentrations in the Irish Sea. Analyses of time series of observational data collected at two sites in the Irish Sea considered the variability to reflect either changes in anthropogenic loading or climatic variability. In this modelling study, the latter supposition is investigated in more detail by considering the response of salinity and tracers in the Irish Sea to variability in climatic forcing. A series of theoretical simulations investigated the roles of tide, wind, baroclinic and far field forcing in the transport and dispersion of nutrients in the Irish Sea. Far field forcing acted to transport and retain the tracer close to the main sampling site in the central Irish Sea (Cypris station). The baroclinic component of flow restricted westward transport of nutrients, with the dominant flow predicted along the coast northwards and out of the region. Direct wind forcing caused high frequency movement of near coastal water masses with high tracer concentrations, thus inducing high frequency variability in predicted concentrations at the Cypris station. Increases in freshwater inflows also caused a shift in these high concentration waters, but at a lower frequency.