Fine scales over the Brazilian coast Abrolhos Banks
The Brazil Current, the southern branch along the south Brazilian coast of the South Atlantic Subtropical gyre follows and interacts with the continental shelf, and transports poleward warm, salty, oligotrophic subtropical waters. At 16°S, it is successively deflected by the Royal Charlotte and Abrolhos Banks, generating semi-permanent systems of cyclonic and anticyclonic eddies, also interacting with intermediate equatorward flows below the thermocline. This mesoscale activity advects toward the surface rich-nutrient waters that boost primary productivity.
Brazil Current encroaching drive intrusion of South Atlantic Central Waters onto the Abrolhos Banks. These banks, an enlargement of continental shelf over 220 km, are the largest and richest modern tropical reef complex in the South Western Atlantic. “Abre os Olhos”, “open your eyes” was the saying of sailors in the past who risked being shipwrecked on these coral reef shoals. The northern flank is very shallow (10-30 m depth) and it includes an arquipelago of five islands -the largest is 1-km long and 35-m high. The topography has been modelled by the rich diversity of reefs over years. Due to the rich endemic biodiversity and unique species of coral reefs, Brazil created its first marine protected area in 1983 in order to limit the impact of local fisheries and tourism.
The Abrolhos Banks are located just south of the Trade Wind regimes and on the northern flank of the South Atlantic High. Hence, the area is under a East-NorthEast regime most of the year, that changes to East-SouthEast influence during late autumn and winter. Consistently, there is a swell regime from the central South Atlantic, with typical wave height of 1-1.5 m enters onto the Banks most of the year. Semi-diurnal tides with largest amplitude of 2.5m propagates from the south to the north of the Banks. The associated tidal currents can reach 50 cm/s in some channels and modify the overall pattern of the southward Brazil Current onto the Banks
The Abrolhos Bank, then the Vitoria-Trindade ridge are strong topographic constraints for the mean flow and generate mesoscale turbulence. Internal tide generation appears south of the ridge. However, the finer scale circulation in geostrophic balance or not, is poorly described in these areas, witnessing wind and waves influence from the South Atlantic, tidal currents, all interacting with the large and mesoscale flows.
The SWOT-Abrolhos campaign aims to characterize the fine scale circulation during mid-autumn over the Banks, provide current and waves observations to be compared with SWOT measurements and regional model simulations. Verify how the present satellite nadir altimetry constellation describe the circulation. To do so, a synoptic survey with the Brazilian Research Vessel Ciencia do Mar IV will be carried out, and two shallow moorings measuring currents and waves will be put in place for three months.
The SWOT-Abrolhos campaign will provide a new set of observations of the fine scale circulation for this area of high bio-diversity; will verify how SWOT samples this circulation ; and will allow dedicated modelling studies in order to characterize the all-scales interactions over this key-topographic region for the South Atlantic circulation.
Fig. Left Ciencia Do Mar IV (photo courtesy of the Federal University of Pernambuco). Right: Eddy Kinetic Energy from the Mercator’s GLORYS12 global reanalysis. Superimposed the SWOT pass n. 20 and the route of the ship (blue). Points (cyan) indicate CTD casts and the two moorings (red). Nadir altimeter satellite groundtracks of Sentinel-6, Sentinel-3A, Sentinel-3B, Jason-3-interleaved are respectively plotted in red, orange, cyan and green.
Principal investigators: Fabrice Hernandez (IRD/LEGOS, firstname.lastname@example.org ), Alex Costa (UFPE/DOCEAN, email@example.com ), Marcus Silva (UFPE/DOCEAN, firstname.lastname@example.org).
Associated researchers: Ariane Koch-Larrouy (IRD/LEGOS), Ramila Viera (UFPE/DOCEAN), Moacyr Araujo (UFPE/DOCEAN), Leo Bruto (UFPE/DOCEAN), Pedro Melo (UFPE/DOCEAN), Vincent Ventrepotte (CNRS/LOV).
Institutes involved in the campaign: Institut de Recherche pour le Développement (IRD), Centre National de Recherche Scientifique (CNRS), Laboratoire Mixte International TAPIOCA, Universidade Federal de Pernambouco (UFPE).
Contact point for the study site: Fabrice Hernandez (email@example.com).