Description and Dynamics of the Santos Bifurcation

Ágata Piffer Braga, University of Massachusetts Dartmouth, New Bedford, MA, United States, Ilson C Da Silveira, Instituto Oceanografico - University of São Paulo, Sao Paulo, Brazil and Avijit Gangopadhyay, University of Massachusetts Dartmouth, New Bedford, United States
In this study we describe the Santos Bifurcation mean pattern and investigate its
modal composition. Also we analyze and compare the local water masses transports for
the Santos Bifurcation split, in terms of annual and intraseasonal means.
The Santos Bifurcation is a mesoscale feature, at intermediate level, offshore of the southeast region in Brazil. This feature is crucial to the understanding of the Brazil Current system and it is located
in a important oil and gas exploration blocks domain, what increases even more the
demands of environmental control in the region.
In order to answer our questions we validated the Mercator Global model output with quasi-synoptic data from the OSE
Brazilian Navy cruise. The results shown virtually constant position of the bifurcation
occurrence over time, although the split transport presented variations. During May and
June the northern branch volume transport is higher, representing around 68% of the sum.
During the October and November months, the split reaches its most discrepancy, when
the southern branch is responsible for more than 74% (more than 2/3) of the sum. In the
other months, despite the transport of the southern branch is higher, it corresponds to
50-60% of the sum. Regarding the modal composition we have found that the south South
Equatorial Current is essentially barotropic, and its first and second baroclinic modes have
less than 3.5% of explained variance. On the other hand, in the Brazil Current system
the baroclinicity increases equatorward, changing from 2.84, South of the bifurcation, up
to 34%, north of the bifurcation, of explained variance. This is the first tridimensional
description of the Santos bifurcation, and its transport variability.