- Several mechanisms can drive vertical velocities in the coastal ocean, including wind-forcing
and through gradients in the vorticity field generated by flow-topography
interactions. A two-layer, steady, wind-driven, analytical model is applied to the major
upwelling systems of Brazil : Cabo Frio (CF) and Cabo de Santa Marta (CSM) regions.
Comparisons are made between the relative roles of wind and flow-topography interaction
in inducing upwelling over these regions. Ekman pumping is the weakest mechanism over
the shelf, but does influence the along-shelf temperature in the CF area. Away from
coastline irregularities, wind-driven upwelling (Ekman transport) dominates over all
mechanisms. However, in the vicinity of capes and coastal features, topographically driven
upwelling plays a significant role, and its transports may vary from 43% to 94% of wind-driven
upwelling. Upstream of capes, topographically driven vertical motions are
downwelling favorable and act against the wind-driven coastal upwelling, while
downstream of capes, they are upwelling favorable, where all mechanisms add up to create
strong upwelling. Peaks in total upwelling in the CF region are about twice as large as those
in the CSM area because the CF region has stronger winds and larger coastline
perturbations than in the CSM region. Observed sea surface temperatures (SST) agree well
with variability in the vertical transports where upwelling peaks are in phase with low
temperature peaks along the coast. Results suggest that on larger scales, the SST variability
along the coast is mainly controlled by wind-driven upwelling, while upwelling due to flow-topography
interaction is responsible for the smaller scale SST variability.
- Mazzini, P. L. F., and J. A. Barth (2013), A comparison of mechanisms generating vertical transport in the Brazilian coastal upwelling regions, Journal of Geophysical Research: Oceans, 118, 5977–5993. doi:10.1002/2013JC008924
|Funding Statement (additional comments about funding)
- This work was primarily supported by a
Brazil-U.S. CAPES/Fulbright scholarship to Piero Luigi Fernandes Mazzini.
Additional support was provided by the U.S. National Science Foundation
grants OCE 0851486 and OCE 0961999.