Mudbelts of the South and Southeast Brazil: a geochemical dataset to investigate anthropogenic impact

Author(s)

Bianca Sung Mi Kim

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto Oceanográfico (IO/DIDC)
• Defense date: 2021-08-30

Examining board members

Rubens Cesar Lopes Figueira; Rodrigo Brasil Choueri; Pablo Muniz Maciel; Michel Michaelovitch de Mahiques

• Advisor: Rubens Cesar Lopes Figueira

Abstract

Mudbelts are mud deposits, located on the continental shelves, which reflect the parallel advective transport to the coast of fine suspended material. Because their composition is mostly fine material, there is a trapping potential for anthropogenic material due to the higher specific surface area of the grains. Thus, the objective was to verify the potential of mudbelts as a record of hydrodynamic and anthropogenic processes through geochemical characteristics, as well as characterizing these deposits, generating the first inventory of metals, As and 137Cs in the region. Metals and As were analyzed by ICP-OES, Hg by VGA-ICP-OES and, 137Cs by gamma spectrometry. Geochemical attributes such as particle size, total organic carbon, nitrogen, and carbon and nitrogen isotopes were also quantified to support the discussion. The levels of metals indicated an absence of contamination, however, the enrichment factor showed a slight tendency of enrichment of these metals over time. Hg showed values only in coastal samples, presenting a gradient toward deeper areas, indicating a punctual source than atmospheric influence. Results of the principal component analysis showed that there is a component linked to atmospheric sources whose behavior along the columns suggests the deposition of tetraethyl lead, added as an additive to gasoline in Brazil, between 1930 and 1989. In addition to distinguishing the southern portion of the southeast, due to the influence of the Rio de la Plata, the discriminant analysis showed that stations with similar sources grouped significantly, with Rio de la Plata as the primary source in the southernmost samples, local input, in the coastal samples near Itajaí region and, the Brazilian current, in the deeper samples from the São Paulo Bight. The 137Cs was found in all stations, as it is a nuclide exclusively from anthropogenic processes, its presence is already an indication of ii anthropogenic influence in these deposits. A multivariate statistical evaluation, together with 137Cs and Hg in the samples allowed us to conclude that the deposits found on the continental shelf are potential sinks of elements/materials arising from anthropogenic activities, and the processes that govern their distribution are strongly linked to oceanographic currents along with the atmospheric deposition. (AU)

• FAPESP's process: 17/08987-0 - Mudbelts of the South and Southeast Brazil: a geochemical dataset to investigate anthropogenic impacts
• Grantee: Bianca Sung Mi Kim
• Support Opportunities: Scholarships in Brazil - Doctorate