Forcing and mixing processes in the Amazon estuary: A study case

Abstract

The research area of this paper is located at the estuary of the Amazon River (Brazil), more precisely at the river mouth (parallels 00° 30'N and 1° 30'N and meridians 049° 00' W and 050° 00'W). This paper presents the results of air movement analysis on the surface atmospheric circulation over the Mouth of the Amazonas River, salinity and temperature measures as well as measurements of currents, carried out along a longitudinal section in the navigation canal region of the Northern Bar of the Amazon River (Barra Norte do Rio Amazonas) in June 2006, during the river flood season in the quadrature tide. This paper purports to contribute towards better interpreting the dynamics effect in hydrodynamic, meteorological and hydrographical parameters at the river mouth. The conclusion drawn from an examination of the issues and related research is that: a) the saline wedge-type stratification can be seen approximately 100km away from the mouth of the Amazon River during the end of the rainy season in the quadrature tide; b) probably, at Amazon estuary quadrature entrainment processes are predominant and are the ones responsible for increased salinity in surface layer, whereas turbulence scattering mixing is secondary to it. c) The large flow of fresh water from the Amazon River at the end of the rainy season implies the displacement of the front saline position over the internal Amazon continental platform. d) The tidal wave shows a positive asymmetry in the canal, with floods lasting less than the ebb tide. This asymmetry decreases towards the ocean, eventually becoming reversed in the presence of a saline wedge. The speeds, however, have a negative asymmetry, with more intense ebb tides, due to the river flow and is more evident by the existence of quadrature tides. e) The progressive behavior of the tidal wave in its propagation in the Northern Channel as well as the effect of morphology on the discharge were observed, with the canal configuration causing the first four anchoring points of the tide to propagate in a straight direction. f) The average climatology of the wind shearing vector shows that it is predominantly zonal over the Atlantic. g) The shearing intensification near the coastal area is according to the zonal wind intensification pattern. The Amazon estuary has unusual characteristics in relation to many established paradigms of estuarine physics; therefore, many more detailed studies are necessary to understand this system’s turbulent processes.