Prehistoric and technogenic loads of Hg in raised and blanket peats from the lower Amur River basin, eastern Asia†

Prehistoric and modern records of Hg in peats from the lower Amur River basin, eastern Asia, were investigated. The Hg accumulation rates (AR) of two ¹⁴C-dated cores from Holocene raised and blanket peats were determined. The low and monotonous Hg AR values of the raised peats determined in the lower part of the core (mean 1.9 μg Hg per m² per year) represent prehistoric Hg inputs from the atmosphere. A sharp increase in Hg AR was determined upward of 52 cm depths (～1600 year BP) (max 17.0 Hg μg per m² per year), which apparently reflects the modern increase in global Hg emissions. The Hg loads in the blanket peats were apparently defined by a combined input from the atmosphere and the watershed followed by diagenetic redistribution. One major peak (max 12.0 μg Hg per m² per year) coincided with increased C_org contents in herbaceous and sphagnum peat formed in the warming and wet climate of the early Holocene. Another peak (11.8 μg Hg per m² per year) correlated both with the accumulation of Fe/Mn compounds and the warm and wet climate of the Holocene Climate Optimum. Minima Hg AR values coincided with the weakening of the East Asia Monsoon and cold and dry climate periods. In the uppermost layers, the Hg AR increased again up to 7.3 μg Hg per m² per year, most likely due to anthropogenic pollution.