EDDIES AND MIXING AT THE ICELAND FAEROES FRONT

The Iceland-Faeroes Front (IFF) is a complex boundary between seven different water masses of Atlantic, Norwegian Sea and Arctic origin. Mixing occurs on many scales several of which were observed during R.R.S. Charles Darwin Cruise 51 in July and August 1990, which has produced one of the most comprehensive quasi-synoptic data sets of this area to date. Towing the undulating CTD profiler, SeaSoar. and using a hull mounted ADCP, the cruise made a large-scale survey of parallel tracks. 50 km apart, across the whole of the IFF and three repeat small-scale surveys, of more closely spaced parallel legs 16 km apart, across a selected length of the front to observe the time development of meanders and eddies. Analysis has shown cyclonic and anticyclonic eddies at scales from 15 km to 70 km diameter. The data indicate that some of these eddies are virtually stationary. The meanders from which these eddies break. however, can be observed to move eastwards along the front in a manner typical of a region of baroclinic instability, and estimates of the phase speed and wavelength are given, These estimates are compared with theoretical models of the instability of fronts due to vertical and horizontal velocity shear. The mixing of Atlantic water north into the Nordic Seas is of great importance climatologically as it is this saline water that, by the process of intense winter cooling, sinks to form the dense water that is eventually recycled back over the Greenland-Iceland-Norway ridges into the Atlantic as North Atlantic deep waters, which then circulate globally. As one of three regions where Atlantic water is mixed north into the Nordic Seas the IFF plays an important role in this global cycle. By the use of simple analytical models of the observed eddies and an estimate of the generation rate of eddies at the IFF, the salt and heat fluxes across the IFF have been calculated. These estimates are of a similar magnitude to previous estimates of fluxes due to intrusive interleaving.