Modelling of the Wyville Thomson Ridge overflow

The exchange of water between the Nordic Seas and the North Atlantic Ocean is part of the global thermo-haline circulation in which warm, saline water flows northwards in the near/surface layers while cold fresher water returns southwestwards at depth. The strength and variability of this circulation is thought to have significant consequences for the climate of northern Europe. Important exit pathways for the cold, dense bottom water are found all along the topographic barrier presented by the Greenland Scotland Ridge - the eastern section of which (between Iceland and Scotland) carries about one third of the total overflow transport into the N Atlantic. The proposed modelling project will focus on the portion of the overflow that is diverted over the Wyville-Thomson Ridge (WTR)and eventually into the Rockall Trough. The climatic importance of this branch of the overflow is already recognised by the establishment by NERC of a field monitoring programme at the site. Sets of mathematical and laboratory models will be developed to support the monitoring activity, in order to understand the processes responsible for the leakage of flow over the WTR and the pathways taken by the overflow as it crosses the WTR and finds its way to the Rockall Trough. Furthermore, the models will quantify the relative fluxes of dense bottom water overflows at different sections of the ridge under different external conditions and will explore the conditions under which the overflow is episodic in nature. The topographic control on the coupling between (i) the overflow leakage over the ridge and (ii) the main overflow transport in the adjacent Wyville Thomson Basin is of crucial importance for the resolution of the above matters and this will receive special attention in the modelling studies. The processes responsible for variability in the Wyville Thomson Ridge overflow will be delineated and the mixing associated with the final cascading descent of bottom water into the Rockall Trough will be measured for a wide range of conditions. The models will vary in domain size, from the regional scale, in which the overflow characteristics of a large part of the Faroese Channels system will be simulated, to the small scale where the detailed structure of the cascading flow and its mixing with the overlying warmer waters will be studied. An important aspect of the research is the interplay between the modelling investigations and the field data, with the predictions of the former informing the analysis of the latter and the future development of the monitoring operations.