Nonlinear Processes in Oceanic and Atmospheric Flows


Marine ecosystem dynamics and horizontal stirring and mixing.

Author: V. Garçon, CNRS.

Names and affiliation of other authors:
V. Rossi (LEGOS), C. López (IFISC), J. Sudre (LEGOS), E. Hernández-García (IFISC)

Oral or poster: Oral presentation

Eastern boundary upwelling zones constitute the largest contribution to the world ocean productivity. They include the Canary and Benguela upwelling systems in the Atlantic ocean and the California and Humboldt upwelling systems in the Pacific ocean. Upwelling areas are spatially heterogeneous, populated with a large variety of mesoscale and sub-mesoscale structures such as fronts, filaments, plumes and eddies. Exchange processes in the transitional area between the shelf and offshore areas are controlled by these sub- and mesoscale structures. They play a major role in modulating the biomass, rates and structure of marine ecosystems. These upwelling systems represent natural SOLAS laboratories. We will present here results from a lagrangian approach based on Finite Size Lyapunov Exponents (FSLE) using altimetric and scatterometric data to estimate the spatial and temporal variations in the lateral stirring and mixing of tracers in the upper ocean within the four upwelling systems.
When investigating links with chlorophyll a concentration as a proxy for biological activity in these upwelling systems, results show that surface horizontal stirring and mixing vary inversely with chlorophyll standing stocks. FSLEs lead to a clear clustering of the systems suggesting that one may use them as integrated and comparative indices for characterizing horizontal dynamical features in all eastern boundary upwellings.

*Satellite images from NASA and ESA

Nonlinear Processes in Oceanic and Atmospheric Flows. July 2-4, 2008. Castro Urdiales, Cantabria, Spain.