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.