A quantitative description of the Norwegian Atlantic Current by combining altimetry and hydrography

Abstract

In this study, we quantified the mean flow and the variability in the Norwegian Atlantic Current (NwAC), including the individual branches, with associated error estimates. We accomplished this by combining repeated hydrographic data in the Svinøy section (at 62° N off the coast of Norway toward the northwest) with absolute dynamic sea surface topography data for the period from 1992–2009. The analysis shows a two-branched structure of the NwAC in this section, with calculated absolute velocities that are largely in accordance with the independent current measurements. The mean volume flux of the NwAC was estimated to be 5.1 ± 0.3 Sv (Sv = 106 m3 s−1). In terms of branches, the estimated 3.4 ± 0.3 Sv in the eastern branch is slightly below previous estimates. The estimated volume flux in the western branch is 1.7 ± 0.2 Sv, but a lack of robust estimates makes a comparison difficult. There is a significant seasonal cycle in the volume transport (the winter maximum is almost twice as large as the summer minimum) with a major contribution from the eastern branch. On the inter-annual scale, the volume flux and temperature are significantly and negatively correlated in both the western branch and in the total. Examining the results showed that increased volume flux is followed by a decrease in the stability of the upper water column, averaged over the Norwegian Sea, and a delay in the phytoplankton spring bloom at the Ocean Weather Station M (66° N, 2° E), by a lag of 1 year. The cause of this decrease in stability, whether a direct effect of the increased volume flux or a consequence of indirect effects, is however beyond the scope of this study.