Stable nitrogen isotope record of lacustrine sediments in Lake Onuma (Northern Japan) indicates regional hydrological variability during the past four centuries

Discriminating natural and anthropogenic forcing on hydroclimatic changes is of fundamental importance for projecting future precipitation distribution under the warming climate. A sediment core (ON12C) obtained from Lake Onuma is used to study the evolution of precipitation in Northern Japan. The age-depth model for the core is based on three identified tephra layers, combined with accelerator mass spectrometry 14C measurements of plant remnants, 137Cs dating, and lithology. Multi-proxy records, including pollen concentration, Alnus pollen percentages and C/N atomic ratios, indicate that the δ15N record reflects nitrogen availability in the catchment where precipitation may exert a significant impact. The δ15N record shows that the precipitation was gradually increasing from 1640 AD, reaching peak strength in the middle of the 19th century, followed by a dry interval during the 20th century. The reconstructed variability in the precipitation from Lake Onuma is supported by other precipitation records from the Asian monsoon region. Solar irradiance is likely responsible for the changes in the summer monsoon precipitation on the centennial timescales during the late Little Ice Age, and the winter monsoon may also have played an important role in snow precipitation. However, the 20th century anomaly indicates that the Asian summer monsoon precipitation variability might be affected by anthropogenic forcing.