TAMIRES DE ARAUJO MORA

TAMIRES DE ARAUJO MORA

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Applications of radon and radium isotopes to determine submarine groundwater discharge and flushing times in Todos os Santos Bay, Brazil
2017 - HATJE, VANESSA; ATTISANO, KARINA K.; SOUZA, MARCELO F.L. de; MAZZILLI, BARBARA; OLIVEIRA, JOSELENE de; MORA, TAMIRES de A.; BURNETT, WILLIAM C.
Todos os Santos Bay (BTS) is the 2nd largest bay in Brazil and an important resource for the people of the State of Bahia. We made measurements of radon and radium in selected areas of the bay to evaluate if these tracers could provide estimates of submarine groundwater discharge (SGD) and flushing times of the Paraguaçu Estuary and BTS.We found that there were a few areas along the eastern and northeastern shorelines that displayed relatively high radon and low salinities, indicating possible sites of enhanced SGD. A time-series mooring over a tidal cycle at Marina do Bonfim showed a systematic enrichment of the short-lived radium isotopes 223Ra and 224Ra during the falling tide. Assuming that the elevated radium isotopes were related to SGD and using measured radium activities from a shallow well at the site, we estimated groundwater seepage at about 70 m3/day per unit width of shoreline. Extrapolating to an estimated total shoreline length provided a first approximation of total (fresh þ saline) SGD into BTS of 300 m3/s, about 3 times the average river discharge into the bay. Just applying the shoreline lengths from areas identified with high radon and reduced salinity results in a lower SGD estimate of 20 m3/s. Flushing times of the Paraguaçu Estuary were estimated at about 3e4 days based on changing radium isotope ratios from low to high salinities. The flushing time for the entire BTS was also attempted using the same approach and resulted in a surprisingly low value of only 6e8 days. Although physical oceanographic models have proposed flushing times on the order of months, a simple tidal prism calculation provided results in the range of 4e7 days, consistent with the radium approach. Based on these initial results, we recommend a strategy for refining both SGD and flushing time estimates.
Evaluation of the activity concentrations of Ra-226, Ra-228 and Pb- 210 in sediments from Antarctica, in the admiralty bay region
2016 - MORA, T.A.; OLIVEIRA, J.; FIGUEIRA, R.C.L.; MAHIQUES, M.M.; SOUSA, S.H.M.
The natural radionuclides of U-238, U-235 and Th-232 series have been used as tracers in research of oceanic processes and management of the coastal region. Some of the natural radionuclides are especially used as tracers of the flux of particulated material into the ocean, which occur both in the water column and/ or in the sediment. The Ra-226, Ra-228 and Pb-210 have helped scientists understand some environmental phenomena occurring on the planet. In this study we performed a radiochemical characterization of a sedimentary column called (1B) of 248 cm collected in the Admiralty Bay, South Shetland archipelago – Antarctica region to determine the activity concentrations (mBq g-1) of Ra-226, Ra-228 and Pb-210 and the its application in a geochronological model to calculate the sedimentation rate. The sediment samples were submitted an acid leaching and then the radiochemical separation of Ra-226, Ra-228 was performed by coprecipitation of the Ba(Ra)SO4 and sequential separation of the Pb-210 by co-precipitation of PbCrO4. These precipitates were measured in gas-flow low background proportional detector. The Ba(Ra)SO4 was measured after 21 days of the precipitation and the PbCrO4 precipitate were measured after 10 days from the final date precipitation. The Pb-210 was detected via gross beta counting of its Bi-210 decay products. The time interval of 21 days for Ra-226 measurement was required for its achieve secular equilibrium with their daughters and the contribution of alpha emitting radioisotopes Ra-223 an Ra-224 were nil. This time interval was also enough to allow the equilibrium Ra-228/Ac-228. The activity concentration of Ra-226 ranged from 11±1 (mBq g-1) to 54±5 (mBq g-1), and the Ra-228 ranged from 48±5 (mBq g-1) to 155±13 (mBq g-1). With the values obtained from activity concentrations of Ra-226 and Pb-210, it was determined the activity concentration of unsupported Pb-210, which is Pb that comes from the atmosphere. The activity concentration of Pb-210 ranged from 7±1 (mBq g-1) to 458±23 (mBq g-1), while unsupported Pb-210 ranged from 7±3 (mBq g-1) to 434±25 (mBq g-1). Based on CIC (Constant Initial Concentration) geochronological model, the sedimentation rate of 0.59±0.05 cm year-1 was estimated in the sedimentary column (1B) coming from the Admiralty Bay region.
Avaliação da concentração de atividade de Ra-226, Ra-228 e Pb-210 em sedimentos provenientes da Antártica na região da Baía do Almirantado
2015 - MORA, TAMIRES de A.
Os radionuclídeos naturais das séries radioativas do 238U, 235U e 232Th são frequentemente utilizados como traçadores em estudos ambientais para a compreensão da dinâmica que ocorre no ambiente marinho e terrestre, como por exemplo, em pesquisas de processos oceânicos e gerenciamento da região costeira. No ambiente marinho, estes radionuclídeos podem ser empregados para estimar fluxos biogeoquímicos de partículas e de nutrientes que ocorrem tanto na coluna dágua, quanto nos sedimentos. Várias pesquisas aplicam a distribuição e o respectivo desequilíbrio dos radionuclídeos naturais no meio ambiente, inclusive em modelos geocronológicos para se obter informações históricas em testemunhos sedimentares. Nesse estudo, realizou-se a caracterização radioquímica das distribuições de 226Ra, 228Ra e 210Pb de uma coluna sedimentar denominada 1B (248 cm de comprimento), coletada na Baía do Almirantado, Antártica. A metodologia utilizada incluiu a lixiviação ácida de amostras de sedimentos, seguida de separação radioquímica sequencial de 226Ra e de 228Ra pela co-precipitação com Ba(Ra)SO4 e de 210Pb pela co-precipitação com PbCrO4. Todas as medidas foram realizadas pela contagem alfa e beta total dos precipitados obtidos, em um detector proporcional de fluxo gasoso de baixa radiação de fundo. As concentrações de atividade de 226Ra e 210Pb foram empregadas para se estimar a atividade de 210Pbnão-suportado presentes no perfil sedimentar 1B. Considerando-se as concentrações de atividade de 210Pbnão-suportado obtidas e a aplicação do modelo CIC(Constant Initial Concentration), foi possível determinar a taxa de sedimentação de 0,59±0,05 cm/ ano.
Activity concentration analysis of Ra-226, Ra-228 and Pb-210 in a sedimentary profile of Admiralty Bay, South Shetland archipelago - Antarctica
2015 - MORA, TAMIRES de A.; OLIVEIRA, JOSELENE de; FIGUEIRA, RUBENS C.L.
Determination of Ra-226, Ra-228 and Pb-210 in sedimentary samples of Admiralty Bay - Antarctica
2015 - MORA, TAMIRES de A.; OLIVEIRA, JOSELENE de; FIGUEIRA, RUBENS C.L.
Evaluation of the activity concentration of sup(226)Ra, sup(228)Ra and sup(210)Pb in sediments from Antarctica in the Admiralty Bay Region
2015 - MORA, TAMIRES de A.; OLIVEIRA, JOSELENE de; FIGUEIRA, RUBENS C.L.; MAHIQUES, MICHEL M.; SOUSA, SILVIA H.M.