Terminal pleistocene organic carbon anomaly in Lake Biwa sediments linked to potential anthropogenic fires: Implications for early human impact on large lake systems

Abstract

Lacustrine sedimentary records serve as valuable archives for reconstructing past fire histories and associated limnological changes. Lake Biwa, the largest freshwater lake in Japan, displays a distinct anomaly in total organic carbon (TOC) concentrations around 13 ka, the origin of which remains uncertain. Previous studies have proposed a potential link between this anomaly and elevated charcoal concentrations, suggesting intensified fire activity. However, the precise temporal relationship between these phenomena remains unclear. In this study, we conducted continuous, high-resolution analyses of TOC contents and charcoal concentrations from sediment cores to investigate their association. Our results reveal a clear synchrony between the TOC anomaly and heightened charcoal concentrations around 13 ka. Quantitative analysis indicates that the direct contribution of charcoal to TOC is negligible. We propose that frequent fire activity during this period likely destabilized soils, enhancing the influx of terrestrial organic matter into the lake and driving the observed TOC anomaly. Notably, the timing of increased fire activity coincides with the earliest evidence of human settlement in the region. Given the absence of similarly elevated charcoal concentrations at other times, our findings suggest that these fires were likely anthropogenic. This study provides one of the earliest potential examples of human-induced impacts on large freshwater lake ecosystems.