On the complementary information provided by satellite images, Lagrangian drifters and a regional numerical model: a case study in the San Matias Gulf, Argentina

Abstract

Satellite images are of great help to understand the ocean circulation. In coastal regions, high-resolution images of chlorophyll-a (chl-a) concentration deliver a very accurate picture of the coastal currents and jets that are often transient features difficult to track otherwise. In this paper we combine clear-sky 750-m-resolution chl-a images with the trajectories of five Lagrangian drifters that have been deployed in the San Matías Gulf (SMG), Argentina, and outputs from a regional numerical model, with the objective to improve the knowledge of the surface circulation in the region. Improving the knowledge of the circulation in SMG is very important to determine critical areas for spawning and recruitment of fishing resources and the distribution of marine biodiversity. However, knowledge of the region is limited because of the scarce observations. The trajectories obtained with the drifters follow, at first order, isobath contours, confirming the presence of a closed circulation cell of approximately 70 km in diameter centered at 41.4°S, 64.5°W, in good agreement with previous studies based on hydrographic data and numerical models. The drifters also highlighted the dominant role of the tidal currents and showed speeds of up to 82 cm/s, suggesting that the dissipation of kinetic energy in the gulf is very high. Near the west coast the trajectories displayed complex circulation patterns that are in very good agreement with the high-resolution satellite images of chl-a. The joint analysis of the satellite images and drifter trajectories shows a strong jet that separates from the coast and tilts from a N-S direction to a SW-NE direction, probably due to persistent northerly winds. These features were not described before and could have important consequences for the ecology of local species.