Long-term fire activity under the East Asian monsoon responding to spring insolation, vegetation type, global climate, and human impact inferred from charcoal records in Lake Biwa sediments in central Japan

Abstract

Records of sedimentary charcoal provide fire histories for assessing the relationship between fires and climate conditions, vegetation, human impact, and other factors. We analyzed charcoal particles in sediments from Lake Biwa in central Japan, dating back to 150,000 years ago. The sediments are well dated, homogenous, and had a constant sedimentation rate, making them ideal for assessing the long-term fire history through charcoal concentration analysis. Low charcoal concentrations in the glacial periods of Marine Isotope Stage (MIS) 2 and 6 indicate that few fires occurred in the periods under the cold climatic conditions. Variations in the microcharcoal concentration between 40,000 and 130,000 years ago, with a periodicity of 21,000–23,000 years, correspond to variations in the spring insolation in central Japan, vegetation type, and global climate, suggesting that the long-term fire activity in central Japan was determined mainly by spring insolation and vegetation type under the influence of global climate change. This finding suggests that insolation changes induced by precession cycles could influence a long-term phenomenon in an area as a direct local effect. Between 16,000 and 3000 years ago, sediments were characterized by an extraordinarily high concentration of large charcoal particles (>50 μm) and the predominance of elongated charcoal particles, suggesting that grassland fires (presumably anthropogenic) occurred frequently in the lakeside area. The frequent fire occurrence presumably contributed to the inflow of a large amount of organic materials, resulting in changes in the aquatic environment of Lake Biwa and/or its adjacent area.