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A geochemical and lead isotopic record from a small pond in a remote equatorial island, Fernando de Noronha, Brazil

Institute of Geosciences, University of São Paulo, rua do Lago, 562, São Paulo 05508-080, Brazil, soniaoli{at}usp.br

Luiz Carlos Ruiz Pessenda

14C Laboratory, Centre for Nuclear Energy in Agriculture, University of São Paulo, Caixa Postal 96, Piracicaba SP 13416-000, Brazil

Suzy Eli Marques Gouveia

14C Laboratory, Centre for Nuclear Energy in Agriculture, University of São Paulo, Caixa Postal 96, Piracicaba SP 13416-000, Brazil

Marly Babinski

Institute of Geosciences, University of São Paulo, rua do Lago, 562, São Paulo 05508-080, Brazil

Deborah Ines Teixeira Favaro

Institute of Nuclear and Energetic Research, IPEN, Caixa Postal 11049, São Paulo, Brazil

A 72 cm long core was collected from Lagoa da Viração (LV), a small pond in the Fernando de Noronha island, northern Brazil. Sediments from the lower section of the core (20—72 cm depth) contain essentially mineral matter, while in the upper section (0—20 cm depth) mineral matter is mixed with organic matter. Lithogenic conservative elements — Si, Al, Fe, Ti, Co, Cr, Cu, Ba, Ga, Hf, Nb, Ni, Y, V, Zn, Zr and REE — exhibit remarkably constant values throughout the core, with concentrations similar to those of the bedrock. The vertical distribution of soluble elements — Ca, Mg, Na, K, P, Mn and Sr — is also homogeneous, but these elements are systematically depleted in relation to the bedrock. LOI, TOC, Br, Se, Hg and Pb, although showing nearly constant values in the lower section of the core, are significantly enriched in the upper section. The concentration profiles of Br and Se suggest that they may be accounted for by natural processes, related to the slight affinity of these elements for organic matter. On the other hand, the elevated levels of Hg and Pb in recent sediments may be explained by their long-range atmospheric transport and deposition. Furthermore, the isotopic composition of Pb clearly indicates that anthropogenic sources contributed to the Pb burden in the uppermost pond sediments.

Key Words: Geochemistry • lake sediments • Fernando de Noronha • mercury • lead isotopes.

The Holocene, Vol. 19, No. 3, 439-448 (2009)
DOI: 10.1177/0959683608101393


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