An inventory of salty and warm subsurface intrusions in the South Brazil Bight

Author(s)

Silva, Danilo Augusto ; Sasaki, Dalton Kei ; Dottori, Marcelo ; Silveira, Ilson Carlos Almeida da ; Belo, Wellington Ceccopieri ; Martins, Renato Parkinson

• Document type: Journal article
• Source: CONTINENTAL SHELF RESEARCH; v. 259, p. 14-pg., 2023-04-12.

Abstract

Subsurface intrusions of salty and warm waters onto the shelf can potentially impact the thermodynamics and biogeochemistry of these relatively shallow water environments. Such thermohaline intrusions are usually associated with double diffusive processes and can enhance the vertical and lateral fluxes. In this work, we characterized subsurface intrusions of Tropical Waters (TW) at the South Brazil Bight (SBB) -a mid-latitude continental shelf, which were detected based on salinity vertical profiles from a historical dataset. We found the intrusions tend to follow the pycnocline and are relatively common year-round, occurring at 27% of the dataset, with a maximum salinity highly correlated with the maximum stratification. Intrusions have different along-shelf characteristics, varying with the shelf width and depth. North of Sao Sebastiao Island (SSI) - at the central portion of the SBB -, intrusions were thicker, saltier, and shallower than the ones found at the south of SSI. These differences could be related to the variations of the Coastal Water (CW) and South Atlantic Central Water (SACW) volume along the shelf and throughout the year. We found that intrusions' thickness presents an inverse correlation with stratification, resulting in thinner intrusions in more stratified environments. This inverse correlation suggests double-diffusively driven intrusions. We apply the Turner Angle method to investigate whether the environment is susceptible to double diffusive processes. This analysis suggests that thermohaline intrusions in the SBB might not be primarily double diffusive. However, the dominance of different double diffusion processes -diffusive convection (salt fingering) at the upper (lower) layer -suggests that these processes influence intrusion growth, steady-state, and erosion. Nonetheless, the mechanism responsible for the initial density perturbation remains unknown and further studies are needed to explore the relationship between the Brazil Current dynamics and thermohaline warm and salty subsurface intrusions. (AU)

• FAPESP's process: 21/13124-6 - The Santos Basin hydrodynamics: the interaction between the Brazil current and the Agulhas eddies
• Grantee: Ilson Carlos Almeida da SIlveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 10/05124-1 - The role of the remote wind forcing in the São Paulo continental shelf dynamics
• Grantee: Marcelo Dottori
• Support Opportunities: Regular Research Grants