The LGM termination in the southeastern Tibetan plateau: View from high-frequency LGM glacier fluctuations in the Boshula mountain range

Abstract

Climate processes that operated during the end of the Last Glacial Maximum (LGM) are remarkable for its global synchroneity. Atmospheric CO₂ concentrations have been widely seen as its cause. However, the stepwise LGM deglaciation of mountain glaciers in both hemispheres complicates this view, and signifies additional factors that likely prompted the onset of LGM termination. Here, we examine LGM climate change in the Hengduan Mountains (HDM), southeastern Tibetan Plateau (TP), based on ¹⁰Be surface exposure dating of moraine boulders (n = 51). The timing of four moraine-building events is constrained to 22.8 ± 1.0 ka, 21.2 ± 0.6 ka, 20.4 ± 0.6 ka, and 19.2 ± 0.6 ka. These precisely-dated events provide convincing evidence of millennial-to centennial-scale glacial activities in the TP during the LGM. We show that these high-frequency glacier fluctuations likely reacted to a combination of changes in regional summer temperature related to sea surface temperatures as well as monsoon precipitation. The pronounced glacial retreat is dated at 19.2 ± 0.6 ka, representing the end of the LGM in the HDM. That is, the onset of LGM termination preceded the rapid CO₂ rise at ∼18 ka. We suggest that the LGM termination in the southeastern TP was initiated by ice-sheet shrinkage, which induced changes in summer temperature and monsoon precipitation via ocean-atmosphere interactions.