Interdisciplinary paleovegetation study in the Fernando de Noronha Island (Pernambuco State), northeastern Brazil

The aim of this research was to reconstruct vegetation changes (with climate inferences) that occurred during the Holocene in the Fernando de Noronha Island, Pernambuco State, northeastern Brazil. The research approach included the use of geochemical (mineralogy, elemental), carbon isotopes (δ13C, 14C) and pollen analyses in soil organic matter (SOM) and sediments collected in Lagoa da Viração and Manguezal do Sueste. The carbon isotopes data of SOM indicated that there was no significant vegetation changes during the last 7400 BP, suggesting that the climate was not the determinant factor for the vegetation dynamics. The pollen analysis of the sediment of a core collected in the Lagoa da Viração showed the absence of Quaternary material in the period between 720 BP and 90 BP. The mineralogical analysis of deeper layer showed the presence of diopside indicating this material was developed "in situ". Only in the shallow part of the core were found pollen of similar plant species of the modern vegetation. The geochemistry and isotope results, in association with the sediment type and pollen analyses of sediment samples of Manguezal do Sueste, indicated variations in the vegetation and in its location since the middle Holocene. Such variations can be associated with climatic events and sea level oscillations and also with anthropogenic events considering the last five hundred years.

Esta pesquisa teve o objetivo de reconstruir trocas de vegetação (com referências climáticas) que ocorreram durante o Holoceno na ilha de Fernando de Noronha, Estado de Pernambuco, nordeste do Brasil. Para o desenvolvimento da pesquisa utilizou-se de análises geoquímicas (minerais, elementar), isótopos do carbono (δ13C, 14C) e análises polínicas em solos e sedimentos coletados na Lagoa da Viração e no manguezal do Sueste. Os isótopos do carbono dos solos indicaram que não houve trocas significativas de vegetação durante os últimos 7400 anos AP, sugerindo que o clima não foi um fator determinante para a dinâmica da vegetação. A análise polínica dos sedimentos da Lagoa da Viração mostrou ausência de elementos quaternários no período entre 720 AP e 90 AP. A análise mineralógica das camadas mais profundas mostrou a presença de diopsídeo, indicando que este material foi desenvolvido"in situ". Somente na parte superficial do testemunho foram encontrados palinomorfos de plantas similares à vegetação moderna. Os resultados geoquímicos e isotópicos, em associação com o tipo de sedimento e as análises polínicas das amostras de sedimento do Manguezal do Sueste, indicaram variações na vegetação e na sua localização desde o Holoceno médio. Tais variações podem estar associadas a eventos climáticos e oscilações do nível do mar e também a eventos antrópicos considerando os últimos quinhentos anos.

Atmospheric mercury deposition over Brazil during the past 30.000 years

Atmospheric Hg deposition over Brazil is presented for the past 30,000 years as a tracer of the different natural and anthropogenic processes affecting the atmospheric environment of Brazil. During most of the prehistoric period, atmospheric deposition rates were rather constant with an average of about 2 mug m(-2) yr(-1). Peak deposition, ranging from 4 to 6 mug m2 y(-1), occurred at least during two periods between 3,300 and 3,600 BP and between 8,500 to 12,000 BP, and during the last glacial maximum (LGM), at about 18,000 years BP. These periods were characterized by drier, colder climates with high frequency of fores fires, as shoen by correlation with coal and pollen distribution data. During the colonial period Hg atmospheric deposition rates were much higher, about four times the prehistoric background and reached 6 to 8 mug m(-2) yr(-1). These increasing Hg deposition rates can only be explained by the large Hg emissions in South and Central America from Spanish silver mines, which emitted to the continent's environment about 200,000 tons of Hg from 1580 to 1820. During the present century, Hg deposition rates varied according to the region of the country. In the Amazon region, where gold mining is the major source of Hg emission to the atmosphere, deposition rates increased continuously during the last 40 years, reaching 8 to 10 mug m(-2) yr(-1). In the industrialized Southeast, Hg deposition was higher during the mild 1960s and 1970s, ranging from 80 to 130 mug m(-2) yr(-1), but decreased to 20 to 30 mug m(-2) yr(-1) in the 1990s, due to the enforcement of emission control policies. However, where Hg emissions are mostly from urban, nonpoint sources, such as along the high urbanized coastal area, Hg deposition, although smaller, increased steadily from the 1940s reaching a maximum at surface sediment layers of about 40.0 mug (-2) yr(-1). The results presented suggest Hg as a reliable tracer of natural (paleoclimatic changes) and anthropogenic (industrial and mining emissions) processes able to affect the atmosphere in Brazil.