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Structure and position of the bottom salinity front in the Amazon Estuary

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Abstract

This paper aims to study the spatial and temporal variability of the haline structure in the Amazon River mouth. A baroclinic three-dimensional numerical model (Delft3D) is configured in order to obtain a yearlong data set of salinity for the domain of interest. The results are analyzed along a cross-shore transect at the Amazon North Channel. A model-based system description is presented considering the differences between average modeled salinities for different scenarios, dry/wet for river discharge, neap/spring for tides, and windy/calm for wind forcing. These results are also presented as Hovmöller graphics, evidencing their relation with forcings. A statistical model is fitted in order to quantify the importance of the three main forcings—namely river discharge, tide, and wind—in the bottom salinity front position. The main conclusions are as follows: (i) Neap tides favor stratification, estuarine circulation, and the landward displacement of the front. River discharge has low influence on bottom salinities. Landward winds promote an increase in surface salinity and reduction at the bottom. (ii) From a maximum displacement of ∼100 km, the bottom salinity front position presents astronomical ranges of 23.2 km for semidiurnal constituents and 66.8 km for long-term constituents. (iii) Time lags (in days) found between forcings and the bottom salinity front position were 2.5 for tidal range, null for discharge, and 6.25 for NE–SW winds. (iv) The statistical model confirmed the major relevance of the astronomic tidal effect over the salinity front dynamics (r 2 = 80 %), surpassing the partial influence of winds (r 2 = 30 %) and river discharges (r 2 = 21 %).

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Acknowledgments

This study was made possible through grants by FINEP (554616/2010-6) and CNPq (309288/2011-8 and 490410/2010-3). Gail Kineke is acknowledged for making available a data set from AmasSeds project. The first and third authors were supported by CAPES Foundation (Ministry of Education).

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Authors and Affiliations

  1. Ocean Engineering Program, COPPE, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

    Ernesto Molinas, Susana Beatriz Vinzon, Carla de Paula Xavier Vilela & Marcos Nicolas Gallo

  2. Water Resource and Environmental Engineering Department, Polytechnic School, Federal University of Rio de Janeiro, LDSC - Centro de Tecnologia, Ilha do Fundão, CEP 21949-900, Rio de Janeiro, RJ, Brazil

    Susana Beatriz Vinzon

Authors
  1. Ernesto Molinas
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  2. Susana Beatriz Vinzon
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  3. Carla de Paula Xavier Vilela
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  4. Marcos Nicolas Gallo
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Correspondence to Ernesto Molinas or Susana Beatriz Vinzon.

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Responsible Editor: Rockwell Geyer

This article is part of the Topical Collection on Physics of Estuaries and Coastal Seas 2012

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Molinas, E., Vinzon, S.B., de Paula Xavier Vilela, C. et al. Structure and position of the bottom salinity front in the Amazon Estuary. Ocean Dynamics 64, 1583–1599 (2014). https://doi.org/10.1007/s10236-014-0763-0

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