The summer gyre in the Western Irish Sea: Shelf sea paradigms and management implications

A cyclonic, near-surface gyre has been discovered above the deep western Irish Sea basin. The gyre, present in spring and summer each year, is formed when stratification isolates a dome of cold bottom water which then drives a baroclinic circulation. Simultaneous observations using ship-mounted, broad-band acoustic Doppler current profiler, towed undulating CTD (conductivity, temperature, depth) and satellite-tracked drifting buoys reveal the detailed horizontal and vertical structure of the gyre. Gyre dynamics have been investigated using a three-dimensional, steady, diagnostic circulation model with realistic bathymetry. The role of the gyre within the existing Bowden-Simpson paradigm of shelf circulation is discussed. Knowledge of seasonal gyre systems is important when formulating management strategies. For example, there is evidence that the Irish Sea gyre acts as a retention system for the planktonic larvae of the commercially valuable Norway lobster ( Nephrops norvegicus , Linnaeus 1758) which inhabits the geographically isolated mud patch beneath the gyre. Moreover, in the event of an accidental summer-time spill, the gyre could also act to retain contaminants, suggesting that this system is at disproportionate risk from environmental damage.