Eddy-induced cross-shelf export of high Chl-a coastal waters in the SE Bay of Biscay

• Published in: Remote sensing of environment Vol. 205; pp. 290 - 304
• Main Authors: Rubio, Anna, Caballero, Ainhoa, Orfila, Alejandro, Hernández-Carrasco, Ismael, Ferrer, Luis, González, Manuel, Solabarrieta, Lohitzune, Mader, Julien
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01-02-2018; Elsevier BV
• Subjects: Altimetry; Basins; Coastal effects; Coastal environments; Coastal waters; Cross-shelf transport; Cyclonic winds; Eddy currents; Exports; FSLE; High-Frequency Radar; Infrared analysis; Infrared tracking; Lagrangian Coherent Structures; Lagrangian connectivity maps; Ocean basins; Ocean mesoscale eddies; Quantitative analysis; Radar; Radar data; Radar signatures; Relative vorticity; Remote sensing; Satellite data; Satellite tracking; Satellites; Shelves; Vorticity; Wind-driven currents; Bay of Biscay; High-Frequency Radar; Cross-shelf transport; FSLE; Ocean mesoscale eddies; Lagrangian Coherent Structures; Lagrangian connectivity maps; Remote sensing
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2017.10.037

Different remote sensing data were combined to characterise a winter anticyclonic eddy in the southeastern Bay of Biscay and to infer its effects on cross-shelf exchanges, in a period when typical along shelf-slope currents depict a cyclonic pattern. While the joint analysis of available satellite data (infrared, visible and altimetry) permitted the characterisation and tracking of the anticyclone properties and path, data from a coastal high-frequency radar system enabled a quantitative analysis of the surface cross-shelf transports associated with this anticyclone. The warm core anticyclone had a diameter of around 50km, maximum azimuthal velocities near 50cms−1 and a relative vorticity of up to −0.45f. The eddy generation occurred after the relaxation of a cyclonic wind-driven current regime over the shelf-slope; then, the eddy remained stationary for several weeks until it started to drift northwards along the shelf break. The surface signature of this eddy was observed by means of high-frequency radar data for 20 consecutive days, providing a unique opportunity to characterise and quantify, from a Lagrangian perspective, the associated transport and its effect on the Chl-a surface distribution. We observed the presence of mesoscale structures with similar characteristics in the area during different winters within the period 2011–2014. Our results suggest that the eddy-induced recurrent cross-shelf export is an effective mechanism for the expansion of coastal productive waters into the adjacent oligotrophic ocean basin.
•Mesoscale winter eddies foster offshore export of coastal productive waters.•Anticyclonic eddies are recurrent features linked to poleward current pulses.•Multiplatform remote sensing data enable the study of mesoscale coastal processes.•Lagrangian diagnostics on HF radar data provide quantification of coastal transport.