Lateral diffusivity coefficients from the dynamics of a SF6 patch in a coastal environment

Type Article
Date 2016-01
Language English
Author(s) Kersale M.1, Petrenko A. A.2, 3, Doglioli A. M.2, 3, Nencioli F.4, Bouffard J.5, Blain S.6, 7, Diaz F.2, 3, Labasque T.8, Queguiner B.2, 3, Dekeyser I.2, 3
Affiliation(s) 1 : Univ Bretagne Occidentale, Lab Phys Oceans, UMR CNRS Ifremer IRD UBO 6523, Brest, France.
2 : Aix Marseille Univ, CNRS INSU, UM 110, IRD,MIO, F-13288 Marseille, France.
3 : Univ Toulon & Var, CNRS INSU, UM 110, IRD,MIO, F-83957 La Garde, France.
4 : Plymouth Marine Lab, Plymouth PL1 3DH, Devon, England.
5 : RHEA ESA ESRIN, I-00044 Frascati, Italy.
6 : Univ Paris 06, Univ Paris 04, Lab Oceanog Microbienne, Observ Oceanol,UMR7621, F-66650 Banyuls Sur Mer, France.
7 : Observ Oceanol, Lab Oceanog Microbienne, CNRS, UMR7621, F-66650 Banyuls Sur Mer, France.
8 : Univ Rennes 1, Geosci Rennes, UMR CNRS 6118, F-35042 Rennes, France.
Source Journal Of Marine Systems (0924-7963) (Elsevier Science Bv), 2016-01 , Vol. 153 , P. 42-54
DOI 10.1016/j.jmarsys.2015.09.003
WOS© Times Cited 2
Keyword(s) Lateral diffusivity coefficient, SF6 tracer, Lagrangian referential, Coastal area
Abstract The dispersion of a patch of the tracer sulfur hexafluoride (SF6) is used to assess the lateral diffusivity in the coastal waters of the western part of the Gulf of Lion (GoL), northwestern Mediterranean Sea, during the Latex10 experiment (September 2010). Immediately after the release, the spreading of the patch is associated with a strong decrease of the SF6 concentrations due to the gas exchange from the ocean to the atmosphere. This has been accurately quantified, evidencing the impact of the strong wind conditions during the first days of this campaign. Few days after the release, as the atmospheric loss of SF6 decreased, lateral diffusivity coefficient at spatial scales of 10 km has been computed using two approaches. First, the evolution of the patch with time was combined with a diffusion-strain model to obtain estimates of the strain rate (γ = 2.5 10- 6 s- 1) and of the lateral diffusivity coefficient (Kh = 23.2 m2s− 1). Second, a steady state model was applied, showing Kh values similar to the previous method after a period of adjustment between 2 and 4.5 days. This implies that after such period, our computation of Kh becomes insensitive to the inclusion of further straining of the patch. Analysis of sea surface temperature satellite imagery shows the presence of a strong front in the study area. The front clearly affected the dynamics within the region and thus the temporal evolution of the patch. Our results are consistent with previous studies in open ocean and demonstrate the success and feasibility of those methods also under small-scale, rapidly-evolving dynamics typical of coastal environments.
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