Source waters contribution to the tropical Atlantic central layer: New insights on the Indo-Atlantic exchanges

Azar, Elias; Piñango, Andrés; Wallner-Kersanach, Mônica; Kerr, Rodrigo

doi:10.1016/j.dsr.2020.103450

Cited by 10 publications

(30 citation statements)

References 65 publications

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“…Tropical Surface Waters (TW) are present in the mixed layer (top ∼100 m), which are characterized by warm and high salinity waters. Intermediate waters are represented by the North Atlantic Central Water (NACW) and South Atlantic Central Water (SACW), both presented between ∼200 and ∼600 m. − NACW is formed at the south flank of the Gulf Stream, while SACW is formed by the confluence of Brazil and Malvinas currents at 35°S and by different modal waters, including the Southern Tropical Indian Modal Water (STIMW) and flows within the SAC until it merges into SEC at 10°S. , Below the SACW, the Antarctic Intermediate Water (AAIW) extends from ∼600 m to more than 1200 m depth. In the Atlantic, it is formed near the Drake Passage, but the region also receives AAIW from the Indian Ocean through the Agulhas Current leakage; it is transported by the South Atlantic subtropical gyre .…”

Section: Methodsmentioning

confidence: 99%

Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean

Miranda

Leonel

Benskin

et al. 2021

Environ. Sci. Technol.

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The dispersion of perfluoroalkyl substances (PFAS) in surface and deep-water profiles (down to 5845 m deep) was evaluated through the Western Tropical Atlantic Ocean (TAO) between 15°N and 23°S. The sum concentrations for eight quantifiable PFAS (∑ 8 PFAS) in surface waters ranged from 11 to 69 pg/L, which is lower than previously reported in the same area as well as in higher latitudes. Perfluoroalkyl carboxylic acids (PFCAs) were the predominant PFASs present in the Western TAO. The 16 surface samples showed variable PFAS distributions, with the predominance of perfluorooctanoic acid (PFOA) along the transect (67%; 11 ± 8 pg/L) and detection of perfluoroalkyl sulfonic acids (PFSAs) only in the Southern TAO. Perfluoroheptanoic acid (PFHpA) was often detected in the vertical profiles. PFAS distribution patterns (i.e., profiles and concentrations) varied with depth throughout the TAO latitudinal sectors (North, Equator, South Atlantic, and in the Brazilian coastal zone). Vertical profiles in coastal samples displayed decreasing PFAS concentrations with increasing depth, whereas offshore samples displayed higher PFAS detection frequencies in the intermediate water masses. Together with the surface currents and coastal upwelling, the origin of the water masses was an important factor in explaining PFAS concentrations and profiles in the TAO.

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Section: Methodsmentioning

confidence: 99%

Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean

Miranda

Leonel

Benskin

et al. 2021

Environ. Sci. Technol.

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“…4; note that f < 0). At the same time, warmer waters (Stramma and England, 1999;Azar et al, 2020) are also found in the west as the SACW in the upper 400 m (this depth slightly varies between datasets), which corresponds to a positive vertical shear of the northward velocity (Eq. 3).…”

Section: Salinity and Temperature Contributions To The North Brazil Undercurrentmentioning

confidence: 99%

“…The STUW is defined by a subsurface salinity maximum in the vertical directions, while the AAIW is defined by a salinity minimum in the vertical directions. The SACW is composed of subtropical mode water 18 (STMW18), which is the warmest among all types of subtropical mode waters (Souza et al, 2018;Azar et al, 2020) in the South Atlantic ocean. The uCDW is expressed as a temperature minimum in the vertical directions (Reid, 1989).…”

Section: Introductionmentioning

confidence: 99%

Influence of Salinity and Temperature Gradients on the Variability of the North Brazil Undercurrent

et al. 2021

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The North Brazil Undercurrent (NBUC) is a narrow (<1°) northward western boundary current in the tropical South Atlantic Ocean. It carries a large volume of water (>16 Sv) and plays an important role in the Atlantic Meridional Overturning Circulation and the South Atlantic Subtropical Cell. Strong salinity and temperature fronts occur over the NBUC region. The role of temperature and salinity gradients on the genesis of NBUC variability has never been explored. This study uses three high-resolution (≤0.1°) and one low-resolution (=0.25°) model outputs to explore the linear trend of NBUC transport and its variability on annual and interannual time scales. We find that the linear trend and interannual variability of the geostrophic NBUC transport show large discrepancies among the datasets. Thus, the linear trend and variability of the geostrophic NBUC are associated with model configuration. We also find that the relative contributions of salinity and temperature gradients to the geostrophic shear of the NBUC are not model dependent. Salinity-based and temperature-based geostrophic NBUC transports tend to be opposite-signed on all time scales. Despite the limited salinity and temperature profiles, the model results are consistent with the in-situ observations on the annual cycle and interannual time scales. This study shows the relationship of salinity-based and temperature-based geostrophic NBUC variations in the annual and interannual variability and trend among different models and highlights the equal important roles of temperature and salinity in driving the variability of NBUC transport.

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“…The western tropical Atlantic Ocean (WTAO) water column is composed by water masses from different sources and transport processes (Azar et al 2021;Pickard & Emery 1990), each one having their own physical properties (Tomczak & Large 1989). Water masses are formed in certain regions in the ocean, where they acquire the physicochemical properties that characterize them (e.g., Azaneu et al 2013;Emery, 2001;Ferreira & Kerr, 2017;Kerr et al 2018;Santos et al 2016;Souza, Kerr & Azevedo 2018;Tomczak 1999).…”

Section: Introductionmentioning

confidence: 99%

“…(Braga & Niencheski 2006;Kress & Herut 2001;Oudot et al 1999;Sardessai et al 2010). The most common biogeochemical parameter applied to characterize water masses is the dissolved oxygen concentration (Silva et al 2010), but dissolved inorganic nutrients may also be used (Azar et al 2021;Pérez et al 1998;Souza, Kerr & Azevedo 2018). Pérez et al (1998) analyzed dissolved inorganic nutrients, along with dissolved oxygen and inorganic carbon in the upper and middle portions of the northeast subtropical Atlantic east of the Azores.…”

Section: Introductionmentioning

confidence: 99%

Biogeochemical Characteristics of Western Tropical Atlantic Ocean Water Masses

Vieira¹,

Cunha²,

Pinho³

et al. 2022

Anu. Inst. Geociênc.

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Water masses are commonly identified according to their conservative parameters. However, there are also studies that use non-conservative parameters, together with the conservative ones, to refine the water masses identification. The aim of this study was to analyze the chemical properties of the water masses in the western tropical Atlantic Ocean (WTAO) according to their inorganic nutrient concentration: nitrate-NO3–, phosphate-PO43–, and silicic acid-Si(OH)4, to set a regional descriptive framework of the water column in view of future comparative studies. We collected full-depth water column samples from 18 oceanographic stations from a latitudinal transect along 38°W, from 02°S to 15°N during the PIRATA-BR XVII and XVIII campaigns, in November 2017 and 2018. We have also used the regional data available from GLODAPv.2 data product to improve the water masses characterization. Six water masses were identified in the region based on their values of potential temperature, salinity, potential density, and neutral density observed in the study area according to the CTD-O2 data: Tropical Surface Water (TSW); South and North Atlantic Central Water (SACW and NACW, respectively); Antarctic Intermediate Water (AAIW); North Atlantic Deep Water (NADW); and Antarctic Bottom Water (AABW). Regarding the nutrient content within each water mass, our results showed that TSW corresponds to a surface oligotrophic water; NACW and SACW have intermediate nutrient concentration values between TSW and AAIW; AAIW showed the highest concentration of phosphate-PO43– (~ 1.35 µmol kg–1) and nitrate-NO3– (~30 µmol kg–1); AABW, on the other hand, was the water mass with the highest silicic acid-Si(OH)4 concentration (~ 80 µmol kg–1), as well as high nitrate-NO3– (~ 25 µmol kg–1) and phosphate-PO43– (~ 1.80 µmol kg–1) concentrations. Additionally, the water column between 300 and 650 m displays an increase in phosphate-PO43– concentrations north of 5oN, associated to a low dissolved oxygen area coupled to the North Equatorial Under Current (NEUC). Long-term, sustained hydrographic and ocean biogeochemistry observations are key to understand how climate change is affecting the ocean, and this study is a contribution to that.

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Source waters contribution to the tropical Atlantic central layer: New insights on the Indo-Atlantic exchanges

Cited by 10 publications

References 65 publications

Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean

Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean

Influence of Salinity and Temperature Gradients on the Variability of the North Brazil Undercurrent

Biogeochemical Characteristics of Western Tropical Atlantic Ocean Water Masses

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