Abstract
We present prehistoric mercury accumulation rates in a dated sediment core from Lagoa da Pata, a remote lake in São Gabriel da Cachoeira, northern Amazon. The sediment samples were subdivided for mercury and radiocarbon analyses. A group of 18 samples have been prepared at ANU for 14C dating by accelerator mass spectrometry (AMS). The dating results show a good correlation with depth in the core, down to 41,500 BP. Three distinct sections are clearly identified in the core. They consist of upper and lower organic-rich layers, separated by an inorganic layer which represents a short period of rapid accumulation around 18 ka BP. The mercury accumulation rate is found to be larger in the upper layer (18 ka to present) than in the lower one (41 ka to 25 ka), by a factor of three. The larger accumulation rate of mercury is probably associated with warmer temperatures and a higher frequency of forest fires during the Holocene.
Highlights
This work is part of a project studying paleoclimatic and paleoenvironmental changes in the Brazilian Amazon over the past 40,000 years, using geochemical tracers of natural and anthropogenic processes
We present prehistoric mercury accumulation rates in a dated sediment core from Lagoa da Pata, a remote lake in São Gabriel da Cachoeira, northern Amazon
The distribution of mercury in lake sediment cores can be used as a tracer of paleoclimatic conditions and may be a powerful tool for the interpretation of paleoclimatology and paleoecology of the region
Summary
This work is part of a project studying paleoclimatic and paleoenvironmental changes in the Brazilian Amazon over the past 40,000 years, using geochemical tracers of natural and anthropogenic processes. It has been shown that changes in atmospheric mercury deposition reflects changes in the ocean temperature and primary production (Vandal et al 1993) of average regional temperature (Marínez-Cortizas et al 1999), and of increases in the frequency of natural fires due to periods of drier climate (Lacerda et al 1999). It reflects past mining activities (Lacerda and Salomons 1998), and the evolution of industrialization (Pirrone et al 1998). Anthropogenic sources of mercury in Brazil are mainly gold mining, and industrial activities (Lacerda 1995, 1997; Lacerda and Salomons 1998) during the second half of the 20th century, but this is not the subject of the present work
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