Authigenic beryllium isotopes reveal fluctuations in the East Asian monsoon over the past two millennia

Reconstructing climate variability beyond human records allows reconstruction of past and prediction of future climate change. However, a lack of high-resolution paleoclimate archives and effective climate proxies has hitherto limited reconstruction of the spatiotemporal evolution of the East Asian summer monsoon (EASM). In this study, the ratio of the meteoric cosmogenic Be-10 (Be-10(met)) to silicate-weathered Be-9 in annually laminated sediments from Maar Lake Xiaolongwan (NE China) was utilized to reconstruct EASM precipitation over the past two millennia. We find two apparent humid periods during the transitions of the Dark Age Cold Period-Medieval Climate Anomaly (DACP-MCA, -700 CE) and MCA -Little Ice Age (MCA-LIA, -1250 CE). The interval of these two humid periods is consistent with previous proposition of similar to 500-yr oscillations of EASM in Northeast Asia. Although there are some phase variabilities, the pattern of temporal variation from 400 to 1600 CE are synchronous with other regional climate records from the EASM region. However, the spatial pattern shows an anti-phase synchronization between the EASM and the transition zone between the EASM and the Indian summer monsoon (ISM), revealing a "dry northeastern and wet southwestern" mode during the MCA. The climate change fluctuations derived here from Be-10(met)/Be-9 in maar lake sediments are more straightforward than Chinese cave delta O-18 records and global temperature anomalies, providing a unique climate proxy for detecting variations of paleo-precipitation flux in specific regions. The overall slight weakening of EASM is consistent with a long-term cooling trend, which is likely regulated by solar irradiance. The apparent decrease of EASM during the transition from MCA to LIA is interpreted as the main control of explosive volcanic eruptions. The internal fluctuations and the spatiotemporal variability of precipitation are likely associated with the integrated effect of ISM and El Nino-Southern Oscillation. (c) 2023 Elsevier Ltd. All rights reserved.