Advective controls on primary production in the stratified western Irish Sea: An eddy‐resolving model study

The Proudman Oceanographic Laboratory Coastal Ocean Modelling System and the European Regional Seas Ecosystem Model are applied at eddy‐resolving (∼1.8 km) scales to the stratified region of the western Irish Sea to investigate the effects of advective transport processes on the ecosystem. We find currents can transport nutrient‐rich water into the otherwise nutrient‐depleted surface layer of the stratified region, fueling intermittent production throughout the summer. The currents involved fall into three classes: large‐scale wind and density‐driven circulation, smaller‐scale eddies, and tidally mediated dispersive phenomena; all appear to play a role in this area. A model experiment without ecosystem advection does not show the intermittent surface production; summer growth only occurs at the thermocline. This experiment gives a significantly lower total annual production of 110 ± 26 g C m −2 yr −1 , compared with 150 ± 40 g C m −2 yr −1 for the full model, which is in better agreement with observational estimates of 140 g C m −2 yr −1 . We calculate summer averages of the terms in the scalar transport equation, which show that advective transport of all nutrients dominates over vertical diffusion above the thermocline in most of the stratified region. The transport of nitrate, ammonia, and phosphate is significantly greater than the transport of silicate. This can be attributed to the lack of silicate recycling in the pelagic ecosystem. Only limited and anecdotal observational evidence exists to support these model results, which points to a need for observations of high spatial and temporal resolution to investigate these processes in conjunction with further model studies.