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A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications
In June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full-depth CTD casts (T, S, Oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 m and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s-1 in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of −0.45. The vorticity at the eddy center reaches −0.8f. Cross-stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m2 s-1. The deep core is nutrients-depleted with concentrations of nitrate, phosphate and silicate 13–18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20–50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll-a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrate the important impact of post-convective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.
Keyword(s)
coherent eddies, submesoscale eddies, nutrients, phytoplankton, glider, Mediterranean Sea
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File | Pages | Size | Access | |
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Publisher's official version | 73 | 8 Mo |