234Th vertical profiles at the são paulo bight as a prospective tracer to estimate export fluxes and particle dynamics (2006)
- Authors:
- USP affiliated authors: FURTADO, VALDENIR VERONESE - IO ; SARAIVA, ELISABETE DE SANTIS BRAGA DA GRACA - IO
- Unidade: IO
- Assunto: OCEANOGRAFIA QUÍMICA
- Language: Inglês
- Abstract: The natural U and Th decay series present several nuclides with half-lives varying from fractions of a second to a few years. This series include many isotopes of radon, polonium, bismuth, lead and thalium and these radionuclides have usually short lives to demonstrate considerable disequilibrium with respect to their precursors. By the other hand, there are in these series nuclides with half-lives that make them useful in tracing a variety of oceanic processes that occur on short time scales. This group includes isotopes of thorium: 234Th (half-life = 24.1 d), 227Th (18.6 d), 228Th (1.9 y); radium: 224Ra (3.64 d), 223Ra (11.1 d); radon: 222Rn (3.8 d) and polonium: 210Po (138 d). From this group, the Th isotopes and 210Po are particle-reactive, while radium and radon tend to remain in solution. Due to its behavior, Th and Po are useful in quantifying the rate of scavenging from solution onto particles and the processes governing the dynamics of particles in the ocean, while Ra and Rn are appropriate tracers for fluid processes such as advection and diffusion. The application of Th isotopes and 210Po as tracers for particle-associated processes have in common the fact that each one is produced by a longer lived parent which is stably dissolved or tends to remain in solution longer than its progeny. In the particular case of Th, the nascent atom can quickly hydrolyze and sorb onto available particle surfaces. In fact, Th has one of the strongest affinitiesfor particle surfaces of all the elements, with a Kd of approximate 106 - 107. Between the short-lived Th isotopes, 234Th has been the focus of the major attention and application to study particle fluxes and deposition in the ocean in the past ten years. This paper presents the determination of 234Th in seawater samples collected at the São Paulo Bight. Seawater samples were collected in February 2003 at four locations: Baía de Ilha Grande (RJ), Ubatuba (SP), São Sebastião (SP) and Santos Bay (SP). Since this study consisted in a preliminary survey on 234Th concentrations at the southern Brazilian coastal area, in each location we initially established a horizontal profile with distances varying from 0 km to 100 km offshore. For these horizontal profiling purposes, surface seawater samples were collected using a 5 L Niskin polypropylene bottle from a rosette. At the wet lab, 2 L of each sample was measured using a graduated cylinder and samples weretransferred to a polyethylene bottle for MnO2 precipitation. Samples for nutrients and particulate matter determination were also collected in all stations. At the latest station, usually 100 km offshore, water samples were collected throughout the water column to a depth of 100 m. Some samples were collected in replicate to evaluate the reproducibility. 234Th was assessed using an improved small volume technique based on its co-precipitation with MnO2. The MnO2 precipitate obtained was filtered in quartz paper and the 234Thactivity was determined via gross-beta measurement of its high energy daughter 234mPa. After 6 half-lives (144 days) the precipitate was measured again, in order to determine the final background count of the geometry employed. This technique included the addition of 229Th as a yield monitor, and recoveries were estimated by using ICP-MS. The procedure adopted showed average recoveries of 80 %.
- Imprenta:
- Source:
- Título: resumos
- Conference titles: Simpósio Nacional de Oceanografia, 3
-
ABNT
OLIVEIRA, Joselene et al. 234Th vertical profiles at the são paulo bight as a prospective tracer to estimate export fluxes and particle dynamics. 2006, Anais.. São Paulo: Instituto Oceanográfico, Universidade de São Paulo, 2006. . Acesso em: 06 maio 2025. -
APA
Oliveira, J., Povinec, P. P., Braga, E. de S., & Furtado, V. V. (2006). 234Th vertical profiles at the são paulo bight as a prospective tracer to estimate export fluxes and particle dynamics. In resumos. São Paulo: Instituto Oceanográfico, Universidade de São Paulo. -
NLM
Oliveira J, Povinec PP, Braga E de S, Furtado VV. 234Th vertical profiles at the são paulo bight as a prospective tracer to estimate export fluxes and particle dynamics. resumos. 2006 ;[citado 2025 maio 06 ] -
Vancouver
Oliveira J, Povinec PP, Braga E de S, Furtado VV. 234Th vertical profiles at the são paulo bight as a prospective tracer to estimate export fluxes and particle dynamics. resumos. 2006 ;[citado 2025 maio 06 ] - Características e distribuição do fósforo sedimentar no verão de 2003 no sistema estuarino-lagunar de Cananéia-Iguape, Estado de São Paulo, Brasil.
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