The reduction of biological production induced by mesoscale 2 mixing: a modelling study in the Benguela upwelling

Recent studies, both based on remote sensed data and coupled models, showed a reduction of biological productivity due to vigorous horizontal mixing in upwelling systems. In order to better understand this phenomenon, we have considered a system of oceanic flow in the Benguela area coupled with a simple biogeochemical model of Nutrient-Phyto-Zooplankton (NPZ) type. For the flow three different surface velocity fields are considered: one derived from satellite altimetry data, and the other two from a regional numerical model at two different spatial resolutions. We computed horizontal particle dispersion in terms of Lyapunov Exponents, and analyzed their correlations with phytoplankton concentrations. Our modelling approach confirms that in the south Benguela, there is a reduction of biological activity when stirring is increased. Two-dimensional offshore advection seems to be the dominant process involved. In the northern area, other factors not taken into account in our simulation are influencing the ecosystem. We provide explanations for these results in the context of studies performed in other Eastern Boundary upwelling areas.I.H-C was awarded a FPI grant from MICINN to visit LEGOS. V.R thanks funding from OCEANTECH project (CSIC PIF-2006) to visit IFISC. V.R. was partly supported 417 by a DGA grant and an Australian Research Council Grant DP1093510 while nishing this work. I.H-C, C.L and E.H-G acknowledge support from MICINN and FEDER through Hiresubcolor project.Peer reviewe