Production of dense overflow waters feeding the North Atlantic across the Greenland-Scotland Ridge. Part 2: An inverse model

Abstract

In Part 1 of this paper ( Deep-Sea Research I, 43, 769–806) an alternative large-scale circulation scheme for the Nordic Seas and the Arctic Ocean was developed, the motivation being to explain the formation and subsequent circulation of the waters that feed the dense overflows across the Greenland-Scotland Ridge into the North Atlantic. The new scheme emphasizes the water changes following the direct advective paths of the warm Atlantic inflow to dense overflows at shallow and intermediate depths. In this paper the new circulation scheme is evaluated quantitatively in terms of an inverse box model. For each water mass, conservation statements are written for mass, heat and salt, and an optimal solution is sought that deviates the least from the observed currents and air-sea fluxes, and yet conserves mass, heat and salt. It is found that the proposed circulation scheme is consistent with the conservation statements, and with the water masses, currents and air-sea fluxes in the region. Estimates of volume transport are in this way assigned to the various branches of the proposed circulation scheme. The inverse model is also used to test various hypotheses, and in particular, it is found that the major site of dense-water formation is the Norwegian Atlantic Current east of the Greenland and Iceland Seas. It is estimated that the intensity of this direct pathway exceeds that of the open-ocean gyres 6:1. Lastly, it is found that the dense water mass formation process within the Norwegian Atlantic Current does not induce a significant seasonal signal in the volume transport. This is consistent with observations of the flow field across the Greenland-Scotland Ridge, which so far have not shown indications that the dense overflows are associated with a seasonal signal.