Spatiotemporal pattern of the East Asian monsoon hydroclimate during the 8.2 ka event inferred from a new speleothem multi-proxy record from SE China

Abstract

Many hydroclimatic records of the 8.2 ka event have been published in the East Asian summer monsoon (EASM) region. However, there are few high-quality records in southeastern China, which limits our deep understanding of the spatiotemporal variation of EASM precipitation during this event. Southeastern China is located in the front region of the East Asian monsoon circulation and particularly sensitive to the EASM changes. This study presents a high-precision (dating error <35 yrs) and high-resolution (∼3 yrs) multi-proxy speleothem record (δ¹⁸O, δ¹³C, trace elements and growth rate) spanning 9.01-7.86 ka B.P. from Shennong Cave, Jiangxi Province, Southeast China. The results show that the 8.2 ka event in southeastern China began at 8.23 ± 0.02 ka B.P. and ended at 8.03 ± 0.03 ka B.P., consistent with Greenland ice cores and other high-resolution geological records within the dating errors. The structure of the 8.2 ka event in southeastern China is characterized by an asymmetric ‘double-plunging’ structure that can be divided into three stages, which is consistent with other stalagmite records from the Asian monsoon region and shows an antiphase pattern with stalagmite records from the South American monsoon region. These features indicate that low-latitude monsoons respond rapidly to high-latitude climate changes, and the internal structure of the event has close correlations. Combined with other high-resolution records from both high and low latitudes, our results are consistent with previous conclusions that freshwater injection into the North Atlantic weakened the Atlantic Meridional Overturning Circulation, and led to a southward shift of the Intertropical Convergence Zone, a weakening of the EASM. We also found that, during the 8.2 ka event, the amplitude of δ¹⁸O variations in the EASM region shows significant differences, with smaller variations in southeastern China compared to northern China, possibly related to changes in moisture sources and regional precipitation. The multi-proxy records of stalagmite SN31 reveal a significant weakening in the intensity of the EASM, resulting in an arid hydroclimate in the study area. This contrasts sharply with the wet climate observed in the region during the 4.2 ka weak EASM period. This contrasts sharply with the wet climate observed in the region during the 4.2 ka weak EASM period, where the EASM precipitation anomalies during the 4.2 ka (or 8.2 ka) event exhibited a dipole (or tripole) pattern across eastern China. Our multi-proxy record also indicates a precursor event occurred between 8.29 and 8.35 ka B.P., as suggested in previous studies, and the study region was characterized by a dry climate. Additionally, the Shennong record shows significant cycles of 4, 10–40 and 286 yrs within the 8.2 ka event, indicating that solar activity and internal forcing mechanisms may have amplified the decadal to multidecadal variability of EASM precipitation during the 8.2 ka event.