Chronology of the Atmospheric Mercury in Lagoa da Pata Basin, Upper Rio Negro Region of Brazilian Amazon

Abstract

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 14 C 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.

An overview of mercury contamination research in the Amazon basin with an emphasis on Brazil

“…Examples of this shift are the Beni and Negro Rivers. Maurice-Bourgoin et al 56 and Santos et al 57 justify their study location as a search for natural background mercury in areas not impacted by gold mining.…”

Palaeofires in Amazon: Interplay between land use change and palaeoclimatic events

“…7) have been identified in the LPT-V sediment core from Lagoa da Pata (Colinvaux et al, 1996a;Santos et al, 1999;Barbosa et al, 2004;Cordeiro et al, 2011;D'Apolito et al, 2013). From 50,000 to 25,000 cal years BP, an organicrich clay with a high (14.4%) average TOC concentration indicates high lake level, with a large delivery of land-derived organic matter as evidenced by C/N weight ratio of approximately 29.0 (Meyers andIshiwatary, 1993, Meyers, 2003).…”

Reevaluation of dating results for some 14C - AMS applications on the basis of the new calibration curves available

“…Each of the calibration curves will represent a mean for the respective hemisphere, but studies regarding Equatorial locations will be better represented by each of them? An example of such a situation can be obtained in [14][15][16][17] where palaeoclimatic studies in the Amazon region are performed. For these studies the Northern Hemisphere dataset was used for calibration.…”