Observations of Internal Tides at the Vitória-Trindade Ridge, South Atlantic Ocean Marcelo R. Toffoli, Afonso M. Paiva, Vladimir S. Costa, Guilherme N. Mill Journal of Geophysical Research Oceans, 2023 The Vitória‐Trindade Ridge (VTR) has been shown, based on satellite altimetry, to be an important region for the generation of internal tides (ITs) that radiate southward and northward into the South Atlantic Ocean. Here, nearly 1 year of unprecedented high‐density in situ velocity and temperature data collected at this undersampled region, were used to investigate and quantify the IT properties and variability. About 90% of the total tidal energy can be accounted for by the IT in the semidiurnal band. The data depict a dominant surface‐intensified mode‐1 vertical structure associated with progressive baroclinic waves, with a less prominent mode‐2 growing in importance from January to June. Values of energy conversion from the barotropic to the baroclinic semidiurnal tides are comparable to other important sites of IT generation in the world ocean. Energy conversion and the highly coherent energy fluxes are strongly related with the spring‐neap cycle, indicative that the observed IT are predominantly generated at the observational site. Fluxes and conversion are modulated by significant changes in the vertical stratification of the upper ocean, which are observed to occur during the different months of observations.
Observing the spread of Agulhas Leakage into the Western South Atlantic by tracking mode waters within ocean rings Luiz Alexandre A. Guerra, Guilherme N. Mill, Afonso M. Paiva Frontiers in Marine Science, 2022 The Agulhas rings transport warm and salty waters that feed the surface limb of the Atlantic Meridional Overturning Circulation. Some studies have focused on the conveying capacity of ocean eddies, and recently, the role of the Agulhas rings in advecting water masses and organisms has been explored. Here we show evidence that the Agulhas rings are responsible for the advection of mode waters from the Cape Basin to the western side of the Atlantic. We analyzed more than 3,200 temperature profiles and 2,400 salinity profiles from historical databases collocated with 52 long-lived Agulhas rings tracked from 1993 through 2016. An automated algorithm was used to identify thermostads in the profiles acquired within the rings. The data revealed mode water layers trapped inside 88% of the rings. The joint distribution of temperature and salinity indicated two types of mode waters in the range 16.2 ± 0.6°C, 35.6 ± 0.1 (Type I) and 12.9 ± 0.7°C, 35.2 ± 0.1 (Type II). The majority (67%) of the rings carrying mode waters had both types detected inside. Moreover, considering only those rings sampled west of the Mid-Atlantic Ridge, we found that 45% of them advected mode waters to the western basin. Therefore, our results demonstrate that, despite the long journey, interaction with the bottom topography and other vortices, ocean-atmosphere exchanges, and decay, the Agulhas rings are responsible for spreading mode waters initially available at the Cape Basin throughout the South Atlantic, contributing to a positive anomaly in temperature and salinity along the eddy corridor joining the Cape Basin to the Brazil Basin.
Volume and Heat Transports by North Brazil Current Rings Luana F. Bueno, Vladimir S. Costa, Guilherme N. Mill, Afonso M. Paiva Frontiers in Marine Science, 2022 A methodology that combines a 24-year long (January 1993 to December 2016) global dataset of eddy trajectories, derived from altimetry, with vertical temperature and salinity profiles from the EN4.2.0 database, derived from XBTs/MBTs, CTDs and Argo floats, was used to reconstruct the mean vertical structure of North Brazil Current (NBC) rings, and to calculate some of their properties. The number of NBC rings formed each year varied from 2 to 8, with an annual-mean formation of 5.3 ± 1.5. During the analyzed period, 112 rings were sampled at least once, at various distances from the center of the rings, leading to a total of 1323 (604) temperature (salinity) profiles available to compute the mean NBC ring, depicting a large, surface intensified, and relatively shallow ring, with intense temperature and salinity anomalies. The meridional volume transport was estimated in 1.3 Sv (1Sv = 106 m3s-1) per ring, leading to an annualized transport of ~7 ± 2 Sv. The amount of South Atlantic Water (SAW) within the mean ring was estimated in ~40 to 60% of the ring volume. According to these estimates, NBC rings may be responsible in different years for approximately 20 to 80% of the northward volume transport associated with the upper limb of the Atlantic Meridional Overturning Circulation (AMOC), and approximately 15 to 55% of the meridional heat transport in the tropical Atlantic.
Coastal Ocean Observing and Modeling Systems in Brazil: Initiatives and Future Perspectives Guilherme Franz, Carlos A. E. Garcia, Janini Pereira, Luiz Paulo de Freitas Assad, Marcelo Rollnic, et al. Frontiers in Marine Science, 2021 Coastal ocean observing and modeling systems (coastal observatories), connected with regional and global ocean systems, improve the quality of information and forecasts for effective management of safe and sustainable maritime activities. The public availability of systematic and long-term information of the ocean is an engine for the Blue Economy, boosting economic growth, employment, and innovation. An overview of some Brazilian initiatives is presented in this paper, involving universities, private companies, federal and state agencies, covering institutions from south to north of Brazil. Although these initiatives focus mainly on ocean physics, integrated efforts can extend the scope to include biogeochemistry and marine biodiversity, helping to address interdisciplinary problems. Existing initiatives can be connected, and new ones fostered, to fill in the gaps of temporal and spatial coverage of ocean monitoring in the vast oceanic area under Brazilian jurisdiction (nationally referred to as the Blue Amazon, in reference to the similar richness of the Amazon Forest). The alignment among national and regional initiatives, as well as with international programs, can be promoted if coordinated by a national-level organization, maximizing the return of public investment and socioeconomic benefits. In light of international examples, possible future institutional arrangements are discussed, leveraging from existing national public policies and international cooperation that Brazil is taking part. The United Nations Decade of Ocean Science for Sustainable Development is a timely opportunity to encourage an institutional arrangement to support and articulate an integrated network of coastal observatories in Brazil.
Internal Tide Generation at the Vitória-Trindade Ridge, South Atlantic Ocean Afonso M. Paiva, Victor B. Daher, Vladimir S. Costa, Simone S. B. Camargo, Guilherme N. Mill, et al. Journal of Geophysical Research Oceans, 2018 Sea surface height data from multiple satellite altimetric missions are analyzed in order to investigate the surface manifestation of internal tides generated at the Vitória‐Trindade Ridge (VTR), in the western South Atlantic Ocean. The VTR is formed by a sequence of submerged seamounts disposed in a west‐east alignment around 20.5°S, extending for over 1,000 km from the Brazilian continental margin to the Trindade and Martim Vaz islands. Point‐wise harmonic analysis of the along‐track sea surface height data, combined with a two‐dimensional plane wave fitting at selected subregions, depicts well‐organized northbound and southbound wave beams radiating from the VTR, and propagating as far as ~1,000 km from the ridge. Energy convergence is observed at a focal point located circa 300 km south of the VTR, associated with a lens effect due to the arc‐shaped ridge. Wavenumber spectra show highest energy associated with wavelengths of 140 and 70 km, close to the theoretical values expected for the first and second baroclinic modes, respectively. Energy fluxes for the mode 1 principal lunar (M2) constituent reach values of 2 to 3 kW/m for the southward beams and 1 kW/m north of the VTR. Judging from its surface signature, the VTR appears to be the most significant internal tide generation site in the western South Atlantic.
DAMEE-NAB: The base experiments Eric P Chassignet, Hernan Arango, David Dietrich, Tal Ezer, Michael Ghil, et al. Dynamics of Atmospheres and Oceans, 2000
