Transports along and across the north-west European shelf edge
John Huthnance1, Jo Hopkins1, Sam C Jones2, Ben R Loveday3, Peter I Miller4, Marie Porter5, John Simpson6, Carl Spingys7, Nataliya Stashchuk8, Vasiliy Vlasenko8, Karen Guihou1, Mark E Inall9 and Weidong Xu10, (1)National Oceanography Centre, Marine Physics and Ocean Climate, Liverpool, United Kingdom, (2)Scottish Marine Institute, Oban, United Kingdom, (3)Plymouth Marine Laboratory, Remote Sensing Group, Plymouth, United Kingdom, (4)Plymouth Marine Laboratory, Remote Sensing Group, Plymouth, PL1, United Kingdom, (5)Scottish Association for Marine Science, Oban, United Kingdom, (6)Bangor University, Ocean Sciences, Bangor, United Kingdom, (7)University of Liverpool, United Kingdom, (8)University of Plymouth, Plymouth, United Kingdom, (9)SAMS, Oban, United Kingdom, (10)King's College, London, United Kingdom
Abstract:
The project FASTNEt – Fluxes across sloping topography of the North East Atlantic – has made a variety of measurements in three contrasted sectors of shelf edge: the Celtic Sea south-west of Britain, the Malin-Hebrides shelf west of Scotland and the West Shetland shelf north of Scotland. Previous studies established the existence of flow along the continental slope in these areas, more persistently poleward in more northern sectors. Modelling is under way to diagnose and estimate the contribution of various processes to transports and exchange along and across the slope.
This presentation describes estimates obtained so far; overall transport estimates from drifters and moored current meters; effective “diffusivity” from drifter dispersion and salinity surveys; other estimates of velocity variance contributing to exchange. In addition to transport by the along-slope flow, possible process contributions which may be estimated include internal waves and their Stokes drift, tidal pumping, eddies and Ekman transports, in a wind-driven surface layer and in a bottom boundary layer.
Overall estimates of exchange across the shelf edge are large, several m2/s (Sverdrups per 1000 km). However, the large majority of this is in tides and other motion of comparably short period, and is only effective for water properties that evolve on a time-scale of a day or less. Exchange due to motion with periods exceeding two days was of order 1 m2/s (2 m2/s) at the Celtic Sea (Malin) shelf edge from short-duration moorings: 11(12) days respectively. An 11-month mooring in deeper water (1000 m) off the Celtic Sea gave equivalent monthly values from 8 to 20 m2/s.
