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Free Content Mode waters and subduction rates in a high-resolution South Atlantic simulation

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Water mass production and destruction in the subtropical South Atlantic gyre is studied. A high resolution numerical model is used to examine regional mode water formation and estimate the associated instantaneous and mean subduction rates. Primitive equation dynamics expressed in depth following (sigma) coordinates are employed.

The main hydrographic and kinematic features of the South Atlantic are faithfully reproduced by the model. In particular, the principle current systems appear and the model exhibits a sequence of ventilated potential vorticity minima on density surfaces coinciding with those of observed South Atlantic mode waters. The formation sequence within the model of these mode waters is described. Net formation rates are estimated using a pseudo-Lagrangian method and by diagnosing the time history of subsurface water mass volumes.

Maximum formation rates occur in the density bands of the mode waters. It is argued that the roots of the model mode waters are found along open ocean late winter outcrops, rather than in the waters entering the gyre from the Brazil Current/Malvinas Current Confluence region. Eddies generate interannual variability in mode water formation and precondition the waters in the outcrop regions for convection. On the other hand, the eddy kinetic energy of the Confluence region is too intense to permit a direct connection between deep convection cells in the western boundary current and those in the open South Atlantic that directly form mode water.

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Document Type: Research Article

Publication date: March 1, 1999

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  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
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