Pathways of surface oceanic water intrusion into the Amazon Continental Shelf

The Amazon Continental Shelf (ACS) is a shallow region (< 100 m), with a maximum width of 330 km, which encloses the northern portion of the Brazilian continental shelf and has great ecological and climatic importance on a global scale. Although important scientific efforts have been made to understand the hydrodynamics of the ACS and the dispersion of the Amazon River plume, there are still few studies that address surface oceanic water intrusion into the ACS. This study describes the existence of preferential surface oceanic water intrusion pathways into the ACS along 3 sectors: Maranhão (MA shelf), Pará (PA shelf) and Amapá (AP shelf). The analysis is based on: (i) 306 surface drifter trajectories along 1344 km of the ACS (provided by the Global Drifter Program) and (ii) 20 years of Lagrangian simulations (with Parcels model forced by currents from the reanalysis GLORYS). The results show that the MA shelf sector is the main pathway for surface oceanic water intrusions into the ACS, corresponding to 56% of the intrusions, followed by PA shelf (43%) and AP shelf (1%). During the austral summer, intrusions occur with a higher frequency in PA and AP shelf. The MA shelf shows weak seasonality in the intrusions. The temporal variability of particle intrusion rates into the ACS is directly related to the variability of the trade winds, and the meso-scale circulation associated with the North Brazil Current and the North Equatorial Countercurrent.