Modeling the seasonal circulation and connectivity in the North Patagonian Gulfs, Argentina

Abstract

The coastal region surrounding the North Patagonian Gulfs is considered one of the most productive areas of the Patagonian Shelf ecosystem. Despite its ecological and economical importance the physical processes that contribute to their fertilization are poorly understood. Here we expand previous studies performing a detailed analysis of the Nuevo (NG) and San José (SJG) gulfs seasonal circulation using a high-resolution numerical model. The circulation patterns in NG are characterized by two distinct modes corresponding to the summer and winter seasons. During summer, stratification decouples the upper and deeper layers of the NG, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. Differential tidal mixing in coastal and deep areas induces the subsurface circulation. As stratification weakens during fall and winter, the circulation patterns are replaced by a large wind-driven anticyclonic gyre in the south and a small cyclonic loop in the north. The western sector of SJG is dominated by two counterrotating gyres generated by tidal rectification while the eastern portion shows sluggish circulation patterns. Consequently, a meridional thermal front develops in summer and winter. Particle tracking experiments indicate that the inner portion of the southern Patagonian shelf replenish the surface layers of the NG and SJG. The deeper layer in NG is mostly renovated by local winter convection. Residence times are very different for NG and SJG; while NG is highly retentive, SJG exchanges with the San Matías Gulf are very effective. There is more connectivity between NG and the coastal region of Valdés Peninsula and the Valdés Front in summer than in winter and a weak seasonal connection between NG and SJG. The connectivity of particles released in SJG with coastal regions of San Matías Gulf are quite important in summer but declines substantially in winter.