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Ocean-estuary exchange variability was studied from 2008 to 2014 at a low latitude coastal plain estuary, Todos os Santos Bay, Brazil, near 13°S. Wind data from Climate Forecast System Reanalysis (CFSR) were used to complement the results of a high-resolution regional ocean model, ROMS. Volume exchange occurred under two distinct circulation patterns, namely Circ + and Circ − , that matched the down-estuary (spring/summer) and up-estuary (autumn/winter) wind regimes respectively. Circ + promoted water-column stratification, while Circ − lasted longer, induced more volume exchange, and reversed the estuarine circulation. In addition, a clockwise lateral circulation (looking into the estuary) occurred during Circ + , whereas a counterclockwise lateral circulation was observed during Circ − . Connectivity was observed between Jaguaripe River and Todos os Santos Bay entrance. Increases in Jaguaripe River discharge, in conjunction with up-estuary winds, promoted a northward advection of the river plume toward the main entrance of the estuary, creating a lateral density gradient over Todos os Santos Bay' western shoal. Our results demonstrate that findings about estuarine circulation at higher latitudes are applicable to low latitude estuaries when dynamical depth and/or basin's width indicate that Earth's rotation is relevant.

Upwelling and uplift events from 2008 to 2012 were analyzed at the South Equatorial Current bifurcation region and in the Salvador Canyon near 13°S. Wind data from Climate Forecast System Reanalysis (CFSR) were used to complement the results of a high-resolution regional ocean model. Upwelling and uplift events occurred predominantly during spring and summer. Previous studies have suggested upwelling implications for fisheries and fish diversity in the region. Uplift events were, on average, longer than upwelling events. Spatially, the strongest events were found over the adjacent shelf of Todos os Santos Bay and Salvador Canyon. This was also the region with the most frequent events. Analysis of forcing mechanisms revealed that wind-driven upwelling, mainly due to upward Ekman pumping, is dominant, with current-driven upwelling providing an additional contribution. Connectivity between Salvador Canyon and Todos os Santos Bay upwelling processes was observed in 20 events, preferentially during the austral summer. This connectivity was linked to a northward coastal undercurrent, which, in turn, advected upwelled/uplifted water from the canyon to the bay-adjacent shelf area. Connectivity occurred under two conditions: i) intense canyon upwelling and ii) low influence of the Brazil Current flow on the shelf. The results of this study demonstrate that wind-driven upwelling contributes directly to the connectivity phenomenon, whereas Brazil Current encroachment inhibits this process. Hence, the results shown herein are widely applicable to upwelling regions under the influence of Western Boundary Currents and/or submarine canyons where upwelling may occur.

This study investigates the propagation of coastal trapped waves (CTWs) along the Brazilian continental shelf between 34°S and 11°S using in situ data combined with the outputs from a high-resolution ocean simulation with HYCOM. The CTWs generation area covers a wide region ranging from the Patagonian shelf to the southern Brazilian shelf. The spectral analysis of coastal sea level series between 54°S and 10.5°S shows three bands of high energy associated with periods from 5 to 12 days, 15–22 days, and 25–40 days. The energy of the CTWs decreases along their propagation for all frequency bands, showing a drastic reduction north of 22°S, due to abrupt variations in the width and depth of the continental shelf between Tubarao Bight and Abrolhos Bank. Their phase speed propagation varies along the coast, being faster (>25 m/s) in the southernmost region (between 42°S and 41°S), reaching ~11 m/s north of 41°S, and reducing to ~3 m/s further north (equatorward of 24°S). The free Continental Shelf Wave theory supports the notion that the intense deceleration north of 24°S can be explained by the narrowing of the continental shelf. The stratification parameter indicates that the Brazilian continental shelf has a barotropic response to wind-generated disturbances.

Estuaries may have ideal technical conditions for tidal energy conversion: strong currents and proximity to the coast and urban/industrial infrastructures. This is the case of the estuary Baia de Todos os Santos, for which a numerical tidal potential density assessment was done. This study used a high resolution numerical configuration of the ocean model ROMS forced with realistic surface and lateral forcing, as well as with tides and river discharges into the bay. Strong currents were found along the main axis of the bay, particularly at the centre and left side of the bay’s main entrance, and for a considerable time fraction. In these regions, speeds higher than 1 m s −1 were found during about 30% of the time leading to a power density around 1300 W m −2 at the surface layer, reaching peaks higher than 2500 W m −2 . The energetic flow at the left side of the inlet is affected by a remarkable sand ridge, the St. Antonio Bank, which intensifies the flow between the shoal and the coast. Operation time versus tidal power (OTP) diagrams for the bay’s entrance show that even with a sharp reduction of operation time (50%) it is still possible to extract a high portion (95%) of the total power density available. Using tidally filtered time series of speed and power density, three important oscillations were found: fortnight associated with M 2 +S 2 spring-neap cycle; semi-annual caused by the S 2 +K 2 interference and responsible for about 1/4th of the total power density; and annual oscillation related with external forcings. The residual flow contributes substantially to the total power density. This contribution is however highly spatially variable, reaching at the bay’s entrance 33% and 17% at the isobaths 10 and 25 m, respectively (at sites separated 2.5 km). Besides the bay’s entrance, some regions inside the bay were identified as potentially interesting for tidal stream energy, but its study requires observations and also additional developments in the modelling configuration.

The use of Expendable Bathythermographs (XBTs) is widespread throughout the world’s oceans. 15 XBT high-density transects are located only in the Atlantic Ocean. However, the only transect that exclusively monitors the Brazil Current (BC) is the NOAA/AOML AX97 transect, running from Rio de Janeiro to Trindade Island. The BC is the Western Boundary Current linked to the circulation of the South Atlantic subtropical gyre. Surface velocity field based on the AX97 XBT data reference transect and two different altimetry datasets (AVISO and ATOBA) are compared with the objective of assessing the impact of different horizontal resolution altimetry products on averaged BC dynamical features. Furthermore, a sensibility study is performed considering different approaches to estimate BC volume transports. Data from 43 AX97 cruises, covering the period from Jan/2004 to Dec/2013 were used. AVISO (ATOBA) data are daily (weekly) and present a spatial resolution of 1/4° (1/12°). AX97 geostrophic velocity values were calculated based on XBT data using the isopycnal of σ θ = 26 . 8 kg/m3 as the reference level of no motion, whereas the altimetry surface geostrophic velocities were obtained based on maps of absolute dynamic topography. About 80.5% (74.4%) of the time, at least one altimetry dataset observed the BC core at AX97 region. ATOBA dataset presented a better performance if compared to AVISO when the BC is highly unstable. Also, in coastal areas, where the flow frequently changes direction, a high-resolution altimetry product (ATOBA) tends to represent the horizontal structure of the BC better than AVISO, where BC horizontal pattern is smoother. Finally, the merge between AX97 data and altimetry datasets presented some inconsistencies when surface currents are in opposite directions. It is recommended to combine AX97 data with another type of data acquired in deeper regions, where near-zero velocities will propagate a smaller error along the water column.

Upwelling events observed from the years 2003 to 2011 were analyzed. Our focus was on the Abrolhos–Campos region (ACR, 15°S–23°S), which is located along the Brazilian Margin and influenced by a western boundary current, the Brazil Current (BC). Satellite sea surface temperature, National Centers for Environmental Prediction (NCEP) and Global Forecast System (GFS) wind data were used to complement the results of a high-resolution regional oceanic model to investigate the occurrence of and the mechanisms responsible for intense upwelling events in this region. These events were more frequent from 20°S to 23°S. Over 90% of the identified upwelling events were influenced by favorable wind stress. Surface Ekman transport was found to be more important for the region from Prado (17°S) to Marataizes (21°S), whereas upward Ekman pumping played a more important role from 22°S to 23°S. Current-driven upwelling processes associated with the location of the BC as well as its velocity and meso-scale activity were also analyzed. The results showed that these mechanisms are highly influenced by the local topography. Topographic effects exerted via the acceleration of the BC are more obvious in the southern ACR, while in the Prado region, BC cyclonic meanders tend to be more relevant. Moreover, eddy-driven upwelling increases in the southward direction after the passage of the Vitoria-Trindade Ridge (20°S), an important submarine chain, which acts to constrain and modulate the southward flow of the BC.

The inner shelf circulation on the Abrolhos Bank is investigated using four years (2002–2005) of moored current and bottom pressure observations from two sites in conjunction with wind data from a nearby meteorological station. This is one of the longest projects monitoring current and sea level along the Brazilian coast. The time variability of the local circulation and main forcings are described. For the first time, both the seasonal and the interannual variabilities are addressed, as are the impact of remote forcing. The cross-shore pressure gradient in the region is mostly set up by along-shore winds, whereas the sub-inertial cross-shore momentum balance is essentially geostrophic, with smaller contributions from the cross-shore wind stress. The along-shelf momentum balance is ageostrophic and mainly occurs between the wind and bottom stresses. South-southwestward along-shore currents occur between October and January, whereas stronger north-northeastward currents are observed in fall and winter. This seasonal cycle is driven by the N–S migration of the South Atlantic High between the seasons. An increasing frequency of the southern winds and, consequently, northward currents are observed between 2002 and 2005 and are related to both the number of fronts reaching the region and the remote effect of fronts that did not cross the area. The cross-shore circulation is weak and mainly forced by the tides. It is suggested that long-period shelf waves that propagate into the region change the inner shelf current field and sea level.

The Regional Ocean Modelling System (ROMS) with embedded nesting capabilities based on AGRIF, configured with a refined grid (1/36°) and realistic forcings (6-hourly winds and surface fluxes, daily large scale oceanic forcings and tides), was implemented to describe the seasonal circulation within the Eastern Brazilian Shelf (EBS) between 10°S and 16°S and its interaction with the mesoscale dynamics associated with the Western Boundary Currents (WBC) which flow over the slope: the Brazil Current/North Brazil Current-Undercurrent (BC/NBC–NBUC), as well as the contribution of the forcing mechanisms on the generation of the shelf/slope currents. The model results show, based on the methodology adopted, that for the northern limit (10°S) the northward flow is the dominant pattern while the southward flow appears as a shallow flow confined to the top 50 m of the water column during the spring/summer seasons. The surface circulation at the inner- and mid-shelves in this region is mostly influenced by the wind forcing, while at the shelf-break the currents are mainly driven by the slope currents during all seasons. In the middle (14°S) and southern (16°S) domains, there is an alternate dominance of the southward/northward flows for the first 150 m of the water column, with the dominance of the southward (northward) flow between October–February (March–September) at 14°S. However, the annual net transport in these regions is oriented southwards. On the other hand, in the sub-surface ( ∼ 150 – 400 m ) the dominance of the northward flow is clear. At 14°S, the inner-shelf circulation is mainly driven by the wind forcing and the mid-shelf circulation is forced by both the wind and the flow over the slope, while the currents at the shelf-break are more influenced by the currents at the slope. Finally, the inner- and mid-shelf currents at 16°S are mainly driven by the wind forcing, while the shelf-break currents present a poor correlation with the wind and a strong influence of the WBC dynamics.

The circulation at the Eastern Brazilian Shelf (EBS), near 13°S, is discussed in terms of the currents and hydrography, associating large-scale circulation, transient and local processes to establish a regional picture of the EBS circulation. The results show that the circulation within the continental shelf and slope region is strongly affected by the seasonal changes in the wind field and meso/large-scale circulation. Transient processes associated to the passage of Cold Front systems or meso-scale activity and the presence of a local canyon add more complexity to the system. During the austral spring and summer seasons, the prevailing upwelling favorable winds blowing from E–NE were responsible for driving southwestward shelf currents. The interaction with the Western Boundary Current (the Brazil Current), especially during summer, was significant and a considerable vertical shear in the velocity field was observed at the outer shelf. The passage of a Cold Front system during the springtime caused a complete reversal of the mean flow and contributed to the deepening of the Mixed Layer Depth (MLD). In addition, the presence of Salvador Canyon, subject to an upwelling favorable boundary current, enhanced the upwelling system, when compared to the upwelling observed at the adjacent shelf. During the austral autumn and winter seasons the prevailing downwelling favorable winds blowing from the SE acted to total reverse the shelf circulation, resulting in a northeastward flow. The passage of a strong Cold Front, during the autumn season, contributed not only to the strengthening of the flow but also to the deepening of the MLD. The presence of the Salvador Canyon, when subject to a downwelling favorable boundary current, caused an intensification of the downwelling process. Interestingly, the alongshore velocity at the shelf region adjacent to the head of the canyon was less affected when compared to the upwelling situation.

The Camamu Bay (CMB) is located on the narrowest shelf along the South American coastline and close to the formation of two major Western Boundary Currents (WBC), the Brazil/North Brazil Current (BC/NBC). These WBC flow close to the shelf break/slope region and are expected to interact with the shelf currents due to the narrowness of the shelf. The shelf circulation is investigated in terms of current variability based on an original data set covering the 2002–2003 austral summer and the 2003 austral autumn. The Results show that the currents at the shelf are mainly wind driven, experiencing a complete reversal between seasons due to a similar change in the wind field. Currents at the inner-shelf have a polarized nature, with the alongshore velocity mostly driven by forcings at the sub-inertial frequency band and the cross-shore velocity mainly supra-inertially forced, with the tidal currents playing an important role at this direction. The contribution of the forcing mechanisms at the mid-shelf changes between seasons. During the summer, forcings in the two frequency bands are important to drive the currents with a similar contribution of the tidal currents. On the other hand, during the autumn season, the alongshore velocity is mostly driven by sub-inertial forcings and tidally driven currents still remain important in both directions. Moreover, during the autumn when the stratification is weaker, the response of the shelf currents to the wind forcing presents a barotropic signature. The meso-scale processes related to the WBC flowing at the shelf/slope region also affect the circulation within the shelf, which contribute to cause significant current reversals during the autumn season. Currents at the shelf-estuary connection are clearly supra-inertially forced with the tidal currents playing a key role in the generation of the along-channel velocities. The sub-inertial forcings at this location act mainly to drive the weak ebb currents which were highly correlated with both local and remote wind forcing during the summer season.