Circulation and fluxes in the sub-polar North Atlantic

This thesis is primarily concerned with inverse techniques which are developed and applied to hydrographic data. A standard linear inverse method with an established history is chosen, the application of which is intended to calculate geostrophic reference currents. The first development of the method is a means to estimate skill in the inversion solution; this is also used to assist in solution selection. The second development of the method concerns the finding of an optimal hydrographic configuration to input to the inversion.The inverse method, with the above modifications, is applied to a data set which consists of three approximately 500-km-sided boxes of CTD stations, with vessel-mounted acoustic Doppler current profiles, collected as the U.K. Control Volume Experiment (CONVEX-91) during summer 1991 on the RRS Charles Darwin in the North Atlantic between Cape Farewell at the southern tip of Greenland and the European continental shelf west of Ireland. The East Greenland Current is represented by selected stations from the International Geophysical Year surveys of the R/V Anton Dohrn, because foul weather prevented CONVEX-91 from sampling there. Climatological wind stress data are used to estimate Ekman fluxes. We derive from the results an estimate of net (poleward) heat flux across the CONVEX-91 region (0.28±0.08 PW), and an estimate for the rate of freshwater gain by the Arctic Basin (0.17±0.04x106m3s-1). The results are compared, where possible, with work by previous authors. A quantified circulation scheme for the part of the Sub-Polar Gyre covered by the survey is presented, in which the most significant difference over previous schemes is that the Denmark Strait Overflow appears very weak - 5-6x106m3s-1, compared with ca. 13x106m3s-1.