Holocene dynamics of the Indian summer monsoon inferred from a high-resolution peat α-cellulose δ18O record on the Tibetan Plateau

Abstract

Knowledge of the variability of the Indian summer monsoon (ISM) is crucial for deciphering hydroclimate dynamics in the Asian Monsoon region during the Holocene. In this study, we present a continuous history of the ISM over the past ∼9700 years using the high-resolution δ18O composition of α-cellulose (δ18Ocell) derived from sedges in a high-altitude peatland in the south-central part of the Tibetan Plateau (TP). The results show that the δ18Ocell values increased gradually from the early Holocene, implying a weakening trend of the ISM. However, a remarkable decrease in δ18Ocell occurred after 2.0 cal ka BP, which is consistent with the recently reported '2-kyr shift' in stalagmite δ18O. Further compilation of reconstructions across Asia demonstrates that the '2-kyr shift' suggests an anomalous intensification of the ISM during the late Holocene. In addition, we propose the concept of a '2-kyr dry event' characterized by the weakest ISM intensity, lasting for approximately a thousand years. The ISM record is influenced by boreal summer insolation and ocean-atmosphere coupling in the Pacific and Indian Oceans. The '2-kyr shift' and '2-kyr dry event' in the ISM region could be linked to the SSTs of the western Arabian Sea and the Pacific warm pool, which superimposed on the reduced solar insolation. This study highlights the δ18O in peat α-cellulose responds well to monsoon intensity at our study site and the important role that ocean-atmosphere circulation plays in regulating centennial-millennial regional hydroclimate variability.