Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13？h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary. 1. Introduction The Caeté river estuary system, encompassed within the Pará-Maranh？o Basin, forms part of the largest continuous mangrove belt in the world and is characterized by a flat coastal landscape dominated by macrotidal conditions. Within this system the estuarine watercourse is well mixed due to shallow water depth, high tidal amplitude [1], and high current velocities (up to 2？m·s？1) [2]. This mangrove system is of vital importance for nationally important commercial fisheries, especially exploitation of the semi-terrestrial crab (Ucides cordatus), which is abundant within inter- and supratidal zones along the Caeté river estuary system. However, despite both the economic and ecological importance of the Caeté river estuary system, as within the majority of estuarine systems in Brazil there is still little information on the dominant physical factors that influence the hydrodynamic processes within this system and consequently little agreement between studies in both total river discharge and drainage area [2, 3]. Macrotides constitute one of the major hydrodynamic
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