Oxygen in the Iberian margin: A modeling study

Highly productive eastern boundary coastal upwelling areas provide interesting environments to study the physical-biological interactions that govern dissolved oxygen (O2) dynamics. The Iberian Upwelling System is located in the northern limit of the North East Atlantic upwelling region, along the Iberian margin off Portugal and Spain. It presents a marked seasonality in the hydrodynamics and it is under the influence of water masses of different origin. Here, we describe the seasonal variability and spatial patterns of O2 in this system taking advantage of the 3-dimensional (3D) ocean model Regional Ocean Modeling System (ROMS). The model has been satisfactorily validated and has allowed a sound 3D description of the O2 dynamics of the coast and adjacent ocean, showing a strong seasonality in the O2 concentration of the upper water column. This seasonality is mainly caused by the deepening and shoaling of the seasonal mixed layer from winter to summer. O2 concentration is high during winter and reaches maximum values in spring due to the seasonal phytoplankton bloom. Minimum O2 values are obtained in summer and autumn. Additionally, the regional circulation of Eastern North Atlantic Central Water (ENACW) noticeably influences the O2 distribution. Over the shelf and slope, more variability is introduced by the intense hydrodynamics of the upwelling season (spring/summer), the slope poleward flow (autumn/winter) and continental runoff.