Summer/winter stratification variability in the central part of the South Brazil Bight

• Quantification of the summer/winter bulk stratification variability in the central South Brazil Bight.
• Demonstration that the inner and middle shelves would be vertically well mixed were not for the buoyancy advection.
• Identification of the two main buoyancy advections, one at the inner shelf and the other at the outer shelf.

Analysis of the hydrographic data collected during seven consecutive high resolution summer/winter cruises in the central part of the South Brazil Bight off the coastal city of Ubatuba confirmed an observable summer/winter stratification variability of the shelf waters. The maximum bulk stratification occurred at mean distances of 85.6 km and 39.1 km from the coast in the austral winter and summer cruises, respectively. Estimates of the equivalent mixing power of the physical processes that increase or decrease the stratification in the inner and middle shelves showed that both shelf regions would be vertically well mixed were it not for buoyancy advection. In the inner shelf, buoyancy advection was associated with the along-shelf transport of low salinity waters originating from river runoff. In the middle shelf, buoyancy advection was due to the oceanic South Atlantic Central Water intrusions toward the coast.