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.

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Consiglio per la ricerca in agricoltura e l'analisi dell'economia agraria (CREA-IT),

Abstract. Adriatic and Ionian seas are Mediterranean subbasins linked through the Bimodal Oscillating System mechanism responsible for decadal reversals of the Ionian basinwide circulation. Altimetric maps showed that the last cyclonic mode started in 2011 but unexpectedly in 2012 reversed to anticyclonic. We related this "premature" inversion to the extremely strong winter in 2012, which caused the formation of very dense Adriatic waters, flooding Ionian flanks in May and inverting the bottom pressure gradient. Using Lagrangian float measurements, the linear regression between the sea surface height and three isopycnal depths suggests that the southward deep-layer flow coincided with the surface northward geostrophic current and the anticyclonic circulation regime. Density variations at depth in the northwestern Ionian revealed the arrival of Adriatic dense waters in May and maximum density in September. Comparison between the sea level height in the northwestern Ionian and in the basin centre showed that in coincidence with the arrival of the newly formed Adriatic dense waters the sea level was lowered in the northwestern flank, inverting the surface pressure gradient. Toward the end of 2012, the density gradient between the basin flanks and its centre went to zero, coinciding with the weakening of the anticyclonic circulation and eventually with its return to the cyclonic pattern. Thus, the premature and transient reversal of Ionian surface circulation originated from the extremely harsh winter in the Adriatic, resulting in the formation and spreading of highly dense bottom waters. The present study highlights the remarkable sensitiveness of the Adriatic-Ionian BiOS to climatic forcing.

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[1] A large (80-90 km in diameter) anticyclonic eddy centered at 43°N, 37-38°E has been the subject of complex investigation in the summer-autumn of 1999 based on measurements carried out during the ''Black Sea'99'' expedition on board of R/V Akvanavt (CTD surveys, deployment of Argos-tracked drifters), analysis of satellite imagery, and using altimetric sea level anomaly maps from merged TOPEX/POSEIDON and ERS-2 satellite data. The eddy was formed as a nearshore anticyclonic eddy (NAE) in the Sochi-Sukhumi region, separated from the coast on 6-9 April 1999, stayed at the center of the eastern basin, which is usually characterized by cyclonic circulation, during about 8 months and decayed near the Turkish coast in December 1999. A compilation of hydrodynamic situations of different years (1993,(1997)(1998)(1999) suggests that similar open sea anticyclonic eddies are frequently the elements of the circulation in the eastern Black Sea in the warm season (April-December). A positive correlation appears to be between eddies' formation and weak macroscale circulation associated with low atmospheric wind forcing. Long lifetime of open sea anticyclones is likely determined by their interaction with neighboring eddies. NAEs' separation from the coast and their transformation into open sea eddies provide horizontal mixing of the upper layer waters and results in deflection of the Rim Current offshore, formation of large meanders of the current around the eddies, and its branching when rounding such features. An example of calculation of cross-shelf water transport relating to an offshore Rim Current branch is presented. It is pointed out that an estimation of the shelf/open sea water exchange based on the box balance model does not contradict the assumption that such exchange is considerably determined by NAEs' separation from the coast.