The Nordic Seas circulation and exchanges.
The Nordic Seas provide the main oceanic connection between the Arctic and the deep global oceans via dense overflows between Greenland and Scotland, into the North Atlantic. An understanding of the circulation and exchanges of this region is vital for any consideration of the implications of high latitude climate change to variability in the Atlantic thermohaline circulation and consequences for regional (European) climate. This thesis makes use of a unique data set of near synoptic hydrographic and LADCP (lowered acoustic Doppler current profiler) measurements across the entire region during summer 1999. The box inverse method is applied to this hydrographic data, using computed geostrophic velocities referenced to detided LADCP measurements. The full summer Nordic Sea flux field (volume, heat and freshwater) is quantified, studying both the exchanges across the openings to the Nordic Seas, and the interior circulation. The total volume transports imply an inflow of 1.3 ± 0.5 Sv to the Nordic Seas from the Arctic Ocean, and a net export of 1.2 ± 0.5 Sv across the Greenland-Scotland Ridge into the North Atlantic. Within the Nordic Seas 4.0 ± 1.3 Sv of the warm saline inflow (s0 < 27.8) are converted to more dense waters, with the majority of the transformation (and ocean-atmosphere heat loss) occurring over the southern part of the Nordic Seas. The total heat convergence within the Nordic Seas is 137 ± 44 TW, giving an average flux of 51 ± 16 W m–2, and the net input of freshwater to the Nordic Seas is 0.059 ± 0.019 Sv. The sensitivity of the summer circulation and fluxes is investigated; considering the formal error estimates from the inverse model, together with the errors implied from inverse and oceanographic sensitivity tests. Supplementary winter data is used to construct a winter circulation providing an indication of significant seasonal variability. This infers that an estimate of the annual mean fluxes based on summer data alone cannot be justified.