Near‐surface circulation of the Nordic seas as measured by Lagrangian drifters

Abstract

In the period June 1991 to August 1993, 107 Argos tracked, drifters drogued to 15 m depth, were released in the Nordic seas (or Greenland, Iceland, and Norwegian Seas). The drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the Iceland‐Faroe Frontal zone and of the Norwegian coast and along the continental margins and their extensions to the Barents Sea and Spitsbergen. The Norwegian Atlantic Current is composed of three distinct streams (two continental margin and one coastal branches) which join into one single swift mean current west of the Lofoten and Vesterålen Islands, where the strongest measured currents are in excess of 110 cm s−1. In addition to the general cyclonic gyre circulation in the Nordic seas, the drifters indicate smaller cyclonic circulation patterns in all the major subbasins, i.e., the Iceland plateau, the Norwegian, the Lofoten, and the Greenland basins. No surface signature of the East Icelandic Current is disclosed by the drifters. Interpolated and low‐pass‐filtered position data were used to construct maps of 15‐m‐depth ensemble mean velocity, velocity variability, and residence time. Vigorous eddy fields are dominant in the strong currents and in the Lofoten basin. Eulerian correlations indicate that they tend to propagate to the west. In contrast, the Iceland plateau appears quiescent, both in the mean and eddy velocities. Single‐particle diffusivities are computed and are found to be in the range 1–7 × 107 cm2 s−1. The corresponding Lagrangian timescale and space scale are 1–3 days and 10–40 km, respectively. These Lagrangian drifter measurements compose the first basin‐scale, accurate near‐surface velocity data set of the Nordic seas.