Amplified and suppressed regional imprints of global warming events on the southeastern Tibetan Plateau during MIS 3–2

Abstract

Large amplitude, rapid climate oscillations, the so-called Dansgaard-Oeschger (D-O) events, are characteristic of the last glacial period. However, lithological evidence of D-O warming events is rare, mainly due to their brevity. Although the Tibetan Plateau (TP) is regarded as especially sensitive to climate change owing to its fragile cryosphere and ecological systems, little is known about the variability of the Indian summer monsoon (ISM) over the TP on millennial to centennial timescales. Here, we use a well-dated loess-paleosol sequence (LPS) in the Niyang River valley on the southeastern TP (SE TP), China, to determine the patterns and timing of millennial-to centennial-scale variations in paleomonsoon strength and to identify their causes. This stratigraphic sequence developed between 39.2 and 21.8 cal kyr BP, covering the late marine isotope stage (MIS) 3/2 transition. Ten paleosol units were identified within the sequence, based on field observations, high-resolution measurements of color, grain size and magnetic properties, as well as mineralogical and geochemical evidence. These paleosol units provide unambiguous evidence of D-O-like abrupt warming events and repeated climatic instability, associated with large-amplitude, abrupt changes of the ISM system over the SE TP. The amplitudes, duration, and frequency of these abrupt ISM strengthening events over the SE TP present unique features, including irregular spacing and varying amplitudes. In general, the amplitude of ISM oscillations was larger during MIS 2 than in the late MIS 3 period. Four well-developed paleosol units suggest that ISM intensity at ∼38.7, 28.3, 25.9 and 23.5 cal kyr BP was notably higher compared to the climate of the Holocene, including the present-day. However, two substantial abrupt warming events of global scale are not recorded within the LZ2 LPS. We suggest that this was because of the amplification and suppression of global warming events over the SE TP, caused by the interplay of global and regional climatic dynamics. Warming amplification occurred during intervals with less snow and glacier ice cover, whereas warming suppression was the result of unusually large snow and glacier ice cover on the TP. We suggest that anomalous fluctuations of the India-Burma Trough of the westerlies to the south of the TP during winter may have played a crucial role in determining the snowfall, snow cover, glacier accumulation, and the transition from warming amplification to warming suppression. Therefore, the anomalous ISM oscillations in the SE TP were the result of the coupling of global and local processes.