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The low-frequency linear eigenmodes of the reduced-gravity shallow-water equations with weak friction are calculated numerically and using an analytic approximation. For basins with a large variation of the Coriolis parameter, large-scale eigenmodes emerge: the eigenfrequencies are integer multiples of the frequency for the gravest mode, which, in turn, has a period given by the transit time of the slowest long Rossby wave. The efolding decay times are comparable to the period and independent of friction. These eigenmodes are excited by stochastic wind forcing and this leads to a weak peak in the spectral response near the frequency of the leastdamped eigenmode. This decadal-frequency peak is most evident on the eastern and western boundaries and in the equatorial region of the basin.

Abstract. The Persian Gulf produces high-salinity water

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Mesoscale dynamics in the Mediterranean Sea have been investigated for years, and anticyclonic eddies are regularly observed features in the Algerian Basin. Here we used the AMEDA eddy detection algorithm to track and monitor a particular anticyclonic eddy from its birth to its death. The analysis of remote sensing data sets (AVISO and sea surface temperature) revealed that this anticyclone split from an Algerian eddy, in October 2015, interacted with the North Balearic Front and merged 7 months later, in May 2016, with a similar Algerian eddy. In early spring 2016, a field experiment during the ProtevsMed 2016 cruise thoroughly investigated this eddy, when it was located near the North Balearic Front, taking high‐resolution (Seasoar) hydrological transects, several Conductivity‐Temperature‐Depth (CTD) casts, and Lowered Acoustic Doppler Profiler measurements. In addition, four drifting buoys were released in the eddy core. These in situ measurements revealed that the vertical structure of this anticyclone was made of two water lenses of very different origins (Atlantic Water above and Western Intermediate Water below) spinning together. In the vicinity of the North Balearic Front, which may act as a dynamical barrier to such oceanic structures, the eddy interacted with a subsurface anticyclonic eddy made of modal water, which fostered cross‐front exchanges generating filaments by stirring. The high‐resolution sampling revealed fine‐scale structures both adjacent to the eddy and within its core.