Footprints of mesoscale eddy passages in the Strait of Otranto (Adriatic Sea)

Abstract

[1] The footprints of mesoscale eddies propagating through the Strait of Otranto are documented from current meter records, and their formation mechanism is hypothesized. Bottom-mounted Acoustic Doppler Current Profilers data, collected during 5 months (November 2006 through April 2007) at a transect in the core of the outflowing Adriatic Dense Water, reveal energetic events that manifest as vertically uniform current vector rotations on a time scale of about 10 days. At the two moorings close to the center of the strait, coherent current vector rotations were in opposite senses. Simulation of the passage of an idealized cyclonic or anticyclonic rigid circular eddy confirms that these opposed rotations could be associated with passages of eddies in the southward direction. Characteristic parameters of the eddies were estimated: the duration was several days, the peak azimuthal velocity was around 10–20 cm/s, and advection velocity below 15 cm/s was predominantly in the southwestward direction. Cyclones were bigger (diameter 30–36 km) than anticyclones (14–24 km), and they traveled at greater depths. The eddy passage left a prominent signal in the thermohaline and turbidity properties. This latter is probably due to sediment resuspension by strong currents and to the advection of the suspended particles through an upstream located canyon. The eddy formation is explained in terms of stretching of the high potential vorticity water column outflowing the Strait of Otranto, a mechanism similar to that observed in the Denmark Strait overflow. Another possible explanation is the baroclinic instability of the overflow layer which results in the eddy formation.