On the Role of Western Boundary Currents to Fertilize Adjacent Continental Shelves at Interannual Scales: A Case Study in the Southwestern Atlantic

Abstract

Exchanges between continental shelves and open ocean basins regulate the transport of heat, salt, and nutrients. In the Southwestern Atlantic, the western boundary current known as the Malvinas Current (MC) fertilizes the outer shelf through recurrent slope-water intrusions. Here we analyze the 2003–2024 interannual variability of satellite chlorophyll-a around 41°S, where the inflection of the 100-m isobath promotes these incursions. The first Empirical Orthogonal Function mode explains 43% of the variance and exhibits a spatial pattern consistent with the MC intrusion zone. Backward Lagrangian simulations reveal that low-chlorophyll periods correspond to waters advected by the onshore MC jet, whereas high-chlorophyll years are linked to offshore-origin parcels likely richer in nutrients. Sea-level anomaly composites indicate that mesoscale eddies near 40°S can block or deflect the MC, favoring intrusions onto the shelf. These results provide new quantitative evidence that variability in boundary-current pathways strongly modulates interannual changes in chlorophyll-a over continental shelves.