Methods of study of variables and processes of marine sedimentary dynamics with natural and artificial radionuclides

Author(s)

Paulo Alves de Lima Ferreira

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC)
• Defense date: 2018-08-31

Examining board members

Rubens Cesar Lopes Figueira; Tufic Madi Filho; Michel Michaelovitch de Mahiques; César de Castro Martins

• Advisor: Rubens Cesar Lopes Figueira

Abstract

The occurrence of natural and artificial radionuclides in the environment can be used as a tool for studies of marine sedimentary dynamics, as these nuclides record environmental processes at both spatial and temporal scales. Within this context, this work aimed at demonstrating the use of natural (210Pb, 226Ra, 230,232Th, 234,238U) and artificial (137Cs) radionuclides in studies of sedimentary dynamics with gamma spectrometry as sole analytical technique. This was done through the application of several mathematical models and methods of radionuclides\' data interpretation. The first application was a quantitative assessment of sedimentation in the Santos-São Vicente coastal system, studying its spatial variations during the last century. Another application was the use of the occurrence and spatial distribution of 137Cs as a stratigraphical tool for age studies in coastal systems of the South Atlantic Ocean. With the results of a mathematical model it was possible to infer values of radionuclide deposition that showed a latitudinal pattern in the levels of this element, consistent with international reports of fallout atmospheric deposition. Finally, a model of sedimentation and age determination based on the relationships between Th and U isotopes was used to estimate sedimentation rates in Quaternary cores from two passive continental margins (South Atlantic western margin and South China Sea margin). The model was validated by statistical comparison with data of stable oxygen isotopes and bio/magnetostratigraphy. The results of this model showed periods with an increase on the 230Th excess activity that could be related to variations on Th deposition rate and the influence of Milankovitch orbital cycles on Th and U deposition. (AU)

• FAPESP's process: 14/08016-6 - Study methods of parameters and processes of marine sedimentary dynamics with natural and artificial radionuclides
• Grantee: Paulo Alves de Lima Ferreira
• Support Opportunities: Scholarships in Brazil - Doctorate