Abstract
Anthropogenic climate change is expected to strengthen upwelling events worldwide, driven by an increase of upwelling-favorable winds. However, Earth System Models (ESM) tend to underestimate regional processes due to their coarse grid resolution, which can lead to local biases. We use a high-resolution ocean model ({1/12}^{circ }) forced by results from the Max-Planck-Institute-ESM to analyze the impact of the RCP8.5 emission scenario on the upwelling of South Atlantic Central Water (SACW) in the South Brazil Bight (SBB). We find a stronger Ekman forcing and a higher spread of SACW over the shelf, but this does not translate into higher vertical velocities at the bottom of the mixed-layer in the end of the century. The increased winds’ effect is essentially balanced by an increase in water column stability due to the surface warming. This is particularly important during austral summer, when this process tends to weaken the upwelling. Vertical velocities decrease significantly along the shelf break. Here, the upwelling regime is governed by the Brazil Current (BC) and slight changes in transport induce large responses in upwelling strength. The consequences are increased sea surface temperatures over most of the shelf, although mitigated by the SACW upwelling and kept below global projections. However, temperatures decrease along Cabo Frio. In this region, shelf break upwelling dominates and is enhanced by a local increase in the BC transport. This highlights the importance of regional processes and, more specifically, of changes in the BC transport for the upwelling in the SBB.
Highlights
The South Brazil Bight (SBB) is located between Cabo Frio and the Santa Marta Cape ( 23◦ to 28.5◦ S, Fig. 1) (Castro and Miranda 1998)
Uncertainties associated with the internal variability within our simulations can be disregarded, and the calculated median based on the ensemble members can be used as a representative case for the Hist/RCP8.5 scenario
We presented further evidence of two distinct upwelling regimes in the SBB
Summary
The South Brazil Bight (SBB) is located between Cabo Frio and the Santa Marta Cape ( 23◦ to 28.5◦ S, Fig. 1) (Castro and Miranda 1998). Of note is that the sudden change in coastline orientation creates intense meso-scale activity along the main BC flow, with a general conversion of eddy- to mean-kinetic energy (Oliveira et al 2009) This meso-scale activity has been suggested to induce shelf break upwelling in the region, through the development of cyclonic meanders that propagates southward from Cabo Frio (Campos et al 2000; Castelao et al 2004; Castro et al 2006). These meanders would be formed due to barotropic shear instabilities associated with topographic Rossby waves (Silveira et al 2000) developed along the BC.
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