Framing Continental Shelf Waves in the southern Adriatic Sea, a further flushing factor beyond dense water cascading

Davide Bonaldo,Sandro Carniel,Mirko Orlić

doi:10.1038/s41598-017-18853-2

Davide Bonaldo, Sandro Carniel + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-18853-2

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Abstract

Continental Shelf Waves (CSWs) are oscillatory phenomena migrating along the continental margins, controlled by the interplay of rotation and bathymetric gradients. Here we combine observational data from five moored current meters and high-resolution hydrodynamic model fields for describing the generation and propagation of CSWs along the Southern Adriatic Margin (SAM, eastern Mediterranean Sea), where the possibility of their occurrence has been theoretically hypothesised but not experimentally observed up to now. Results show that in spring 2012 a train of CSWs with 35–87 km wavelength and 2–4 day period was generated on the northern sectors of the SAM and propagated southwards along its western slope. Along their path, CSWs modify their apparent frequency and oscillation mode as an effect of the background current and scattering caused by changes in the continental margin morphology. This signal appears as a persistent feature triggered by the inflow of a dense water vein formed in the northern Adriatic Sea, propagating upwelling and downwelling patterns along broad sectors of the continental slope. CSWs thus appear as an additional remote-controlled mechanism for cross-shelf exchange of water, sediment and nutrients in the SAM, besides the well-acknowledged dense water downflow along preferential pathways driven by local topographic constraints.

Highlights

Topographic waves are a category of oscillatory features associated with a modulation in the potential vorticity field induced by topographic gradients into a quasi-geostrophic flow[1,2,3] in the ocean
In this study we focus on a particular kind of topographic waves propagating along the continental margin and trapped thereby as an effect of the pronounced bathymetry, usually referred to as Continental Shelf Waves[11,12,13,14] (CSWs), in the southern Adriatic Sea (Fig. 1a,e)
In this work we provide a dynamical characterisation of these pulsing features and their implications for continental margin processes and regional circulation

Summary

Introduction

Topographic waves are a category of oscillatory features associated with a modulation in the potential vorticity field induced by topographic gradients into a quasi-geostrophic flow[1,2,3] in the ocean. Along with the development of a sound theoretical framework for such waves, their dynamics and implications for coastal dynamics were progressively explored by means of observational campaigns, generally relying on current meter arrays deployed as single or composite moorings[4,5]. This permitted to highlight, for instance, the role of topographic waves in modulating heat and momentum fluxes below the thermocline on the Gulf Stream[4,6] and coastal upwelling along the Australian coasts[7]. The possible occurrence of CSWs on the Southern Adriatic Margin (SAM) was theoretically postulated back in 199017, but up to now never experimentally demonstrated

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