Abstract
Abstract. One of the main purposes of the BOUM experiment was to find evidence of the possible impact of submesoscale dynamics on biogeochemical cycles. To this aim physical as well as biogeochemical data were collected along a zonal transect through the western and eastern basins of the Mediterranean Sea. Along this transect 3-day fixed point stations were performed within anticyclonic eddies during which microstructure measurements of the temperature gradient were collected over the top 100 m of the water column. We focus here on the characterization of turbulent mixing. The analysis of microstructure measurements revealed a high level of turbulent kinetic energy (TKE) dissipation rate in the seasonal pycnocline and a moderate level below with mean values of the order of 10−6 W kg−1 and 10−8 W kg−1, respectively. The Gregg Henyey (Gregg, 1989) fine-scale parameterization of TKE dissipation rate produced by internal wave breaking, and adapted here following Polzin et al. (1995) to take into account the strain to shear ratio, was first compared to these direct measurements with favorable results. The parameterization was then applied to the whole data set. Within the eddies, a significant increase of dissipation at the top and base of eddies associated with strong near-inertial waves is observed. Vertical turbulent diffusivity is increased both in these regions and in the weakly stratified eddy core. The stations collected along the East–West transect provide an overview of parameterized TKE dissipation rates and vertical turbulent diffusivity over a latitudinal section of the Mediterranean Sea. Strong TKE dissipation rates are found within the first 500 m and up to 1500 m above the bottom. Close to the bottom where the stratification is weak, the inferred vertical turbulent diffusivity can reach Kz≃10−3 m2 s−1 and may therefore have a strong impact on the upward diffusive transport of deep waters masses.
Highlights
During the last two decades, increasing evidence has shown that vertical transport is a key factor controlling biogeochemical fluxes in the ocean
Two main processes account for vertical transport: upwelling resulting from divergent Ekman transport and turbulent mixing
Anticyclonic eddies have been the subject of several studies since processes intrinsic to the eddy dynamics locally enhance the vertical transport of nutrients in the euphotic layer (McGillicudy et al, 1999; Ledwell et al, 2008)
Summary
During the last two decades, increasing evidence has shown that vertical transport is a key factor controlling biogeochemical fluxes in the ocean. Anticyclonic eddies have been the subject of several studies since processes intrinsic to the eddy dynamics locally enhance the vertical transport of nutrients in the euphotic layer (McGillicudy et al, 1999; Ledwell et al, 2008). Turbulent dissipation rates are characterized from microstructure measurements in the upper 100 m and are favorably tested against parametrization of energy dissipation based on fine-scale internal wave shear and strain This parameterization is applied in order to characterize vertical mixing within the full depth range of the eddies and the effect of possible internal wave trapping is discussed. The location of mixing hot spots and their possible impact on the Mediterranean overturning circulation is briefly discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
