Aspects of the circulation in the Rockall Trough

An investigation is made of the circulation and structure of the water masses in the Rockall Trough in spring, combining the results of a recent synoptic survey (May 1998) with those from a high-resolution ocean circulation model. In the near-surface layer, saline flows are carried northwards by a “Shelf Edge Current” around the eastern slopes, possibly with some branching in the northern Trough. Fresher waters from the west inflow between 52 and 53°N and partially mix with these saline flows in the southern Trough, so that waters of intermediate salinity are also swept northwards. In the southern approaches to the Trough, Labrador Sea Water (LSW) also flows strongly in from the west between 52 and 53°N, and while much of this turns south, a proportion penetrates north to join a cyclonic gyre in the Trough extending to 56.5°N. The northwestern limb of this gyre is fed by, and mixes with, more saline waters which result from overflows across the Wyville–Thomson Ridge. Furthermore, salinity and CFC data suggest episodic inflow of LSW into the central Trough. The circulation of the North East Atlantic Deep Water in the Trough follows a cyclonic pattern similar to, and lying below, that of the LSW. The Wyville–Thomson Ridge overflows in the model extend to higher densities than in the survey, are topographically steered southwestward down the Feni Ridge system, and eventually join a deep cyclonic circulation in the North East Atlantic basin. Overall, the model and the observations are in good agreement, particularly in the central Rockall Trough, and this has allowed conclusions to be drawn which are significantly more robust than those which would result from either the survey or the model alone. In particular, we have been able to infer cyclonic circulation pathways for the intermediate and deeper waters in the Rockall Trough for (we believe) the first time. The study has also contributed to an ongoing community effort to assess the realism of, and improve, our current generation of ocean circulation models.