High-Resolution Lacustrine Records of the Late Holocene Hydroclimate of the Sikhote-Alin Mountains, Russian Far East.

There is little information about moisture changes in different altitudinal belts in mountainous regions of the southern Russian Far East. We present ecological and taxonomic compositions of the diatom flora and identify the botanical composition of peat in small mountain lake/mire complexes located in the Central Sikhote-Alin Mountains, within large landslides on the paleovolcanic slopes. Frequent changes in diatom assemblages and peat-forming plants indicate unstable hydroclimatic conditions with varying degrees of wet and dry conditions up to the overgrowth of the lakes. Frequent change in sphagnum mosses with different trophic preferences was identified. The chronology is based on 11 radiocarbon dates. Accumulation rates reached 1.7-1.9 mm/year, and the temporal resolution for the reconstructions was up to 30-40 yr. The tendencies of lake evolution depended on different scale hydroclimatic changes over the last 4400 yr. The most detailed data for the last 2600 yr were obtained from the Nizhnee Lake sequence, which is more sensitive to climatic changes. The main reason for the change in the hydrological regime of the lakes was variations in precipitation during short-term climatic changes. The sediment record of moisture fluctuations is relatively well correlated with regional patterns reflecting summer monsoon intensity and cyclogenesis activity.

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 Corg 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.