On the formation and evolution of Cabo Frio upwelling

Authors

Arthur Ramos - Centro de Hidrografia da Marinha
Leandro Calado - Instituto de Estudos do Mar Almirante Paulo Moreira

Abstract

Among the upwelling systems along the Brazilian coast, probably the most well known and studied is the one near Cabo Frio. Occurring in both spring and summer, this upwelling system is stronger during the summer but more frequent in spring due to the presence of strong northeast winds in the region.

These winds force the rise of the South Atlantic Central Water (SACW) near Cabo Frio. The presence of the SACW in the coastal zone may cause a gradient of around 10°C between onshore and offshore areas. In addition to the winds, the Cabo Frio region has some physical features that contribute to upwelling events. These include: a wider continental shelf, an abrupt change in coastline direction, and the interaction between the upwelling and meso-scale system via Brazil Current meanders.

Although well studied in its path along the coast of Rio de Janeiro, the upwelling plume around the Cabo Frio Islands and around the city of Arraial do Cabo is not well understood. This presentation investigates the upwelling formation mechanisms and the plume pathways in this region.

ROMS is used to simulate the dynamics of the upwelling plume around Cabo Frio Islands. A one-way (coarse to fine) nesting approach was used. Three experiments were conducted: one with only the tide as a forcing, one with only the wind, and one with both forcings. The results show that i) wind is the most important mechanism in the area; ii) SACW enters in the Cabo Frio Island bay along the bottom of the north channel; and iii) cold water is constrained by the bathymetry in the south channel. The SACW could also be seen around the Cabo Frio Islands, outside the bay. At the surface, the wind prevents the entrance of the upwelled SACW in the island bay and follows its path to the south.