HR: 12:05h
AN: OS22A-08    [Abstracts]
TI: Tidal Asymmetry in Amazon Estuary
AU: * Vinzon, S B
EM: susana@oceanica.ufrj.br
AF: Federal University of Rio de Janeiro, Caixa Postal 68508, Centro de Tecnologia, C-203, Rio de Janeiro, RF 21945-970, Brazil
AU: Gallo, M N
EM: marcosgallo@oceanica.ufrj.br
AF: Federal University of Rio de Janeiro, Caixa Postal 68508, Centro de Tecnologia, C-203, Rio de Janeiro, RF 21945-970, Brazil
AU: Fernandes, R D
EM: duarte@oceanica.ufrj.br
AF: Federal University of Rio de Janeiro, Caixa Postal 68508, Centro de Tecnologia, C-203, Rio de Janeiro, RF 21945-970, Brazil
AB: Estuaries and coastal areas are the last reservoir of fine sediments yield in the continental basins. One of the most interesting questions for each particular system is where the fine sediments are trapped in larger quantities. In the early 90's, a thorough measurement project was held over the Amazon Continental Shelf and coastal zone. One of the results of this project was the register of a huge amount of sediments in suspension over the Shelf, where the turbidity maximum would be located. In order to promote the formation of a turbidity maximum zone, conditions for trapping and deposition are necessary as well as a source of energy to keep sediments in suspension, in general in a feed back way. Several mechanisms can be pointed as responsible for trapping sediments in estuaries and coastal areas. Sediments are carried by currents and the question could be established as which are the main features in the hydrodynamics which contributes to the formation of the turbidity maximum? Flocculation induced by the changes in the flow structure, mainly the reduction in turbulence, can be regarded as one of the mechanisms which contribute to the formation of the turbidity maximum In fact, in-situ measurements showed floc sizes as big as 600µm over the Amazon Shelf. Other feature which strongly affects hydrodynamics and hence trapping sediments is the creation of recirculation zones, related to the estuarine morphology, this aspect, especially important in open areas, is also important in the Amazon Shelf. The role of the shear stress asymmetry and the transport capacity asymmetry both related to the salt stratification structure are also shown as important mechanisms for sediment trapping in this environment. Focusing the understanding of the dynamics of fine sediments in Amazon estuary, the tide asymmetry in the Amazon estuary is analyzed. Changes in the vertical tide asymmetry are observed along the estuary. A positive vertical tide asymmetry is observed in the estuarine region with river influence, which is not indicative of positive velocity asymmetry, as is currently considered for tidal bays, without significant river discharge. Over the Shelf, where salinity intrusion and fluid mud bottom layers occur, negative tidal asymmetry is observed. Causes for the changes of the asymmetry and their consequences for the sediment transport are addressed in this work.
UR: http:www.oceanica.ufrj.br/costeira/projetos/amazonas/index.html
DE: 3020 Littoral processes
DE: 3022 Marine sediments: processes and transport
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly