Wind, tides, and waves in a shallow coral reef system: observations and modeling of circulation in Tamandaré (Brazil)

Coral reef circulation is governed by the combined effects of waves, tides, winds, and reef morphology, which have significant implications for sediment transport, connectivity, and ecosystem resilience. This study presents the first investigation of the hydrodynamics of the Tamandaré reef system in northeastern Brazil, a shallow, channelized fringing reef subject to persistent trade winds. In situ observations and a coupled depth-averaged hydrodynamic and wave model (Delft3D-SWAN) suggest that circulation within the inner reef lagoon is strongly associated with wind forcing at subtidal timescales, while tidal water-level variations strongly modulate current intensity through changes in water depth. Although energetic offshore waves are present, wave forcing appears to play a more limited direct role at the measurement site and at the resolved timescales, although its contribution at the reef scale, particularly through unresolved processes such as infragravity motions, cannot be excluded. Depth-averaged currents display coherent seasonal reversals, with a dominant subtidal mode accounting for more than 80-90% of the observed variance and closely linked to wind variability. Numerical simulations reproduce persistent inflow through reef channels and seasonally varying outflow pathways, contextualizing the observations spatially. Collectively, these results are consistent with a wind-driven, tidally modulated circulation regime, underscore the influence of reef morphology on forcing dominance, and provide a physical baseline for understanding circulation in trade wind-influenced reef systems.