Abstract
The eastern Tibetan Plateau (TP) is a climatically sensitive area affected by the Indian Summer Monsoon (ISM). A new pollen record from a lacustrine sediment in Mao County shows that the study area was covered mainly by shrubs and herbs during the last deglaciation, indicating open and sparse forest grasslands. Hydrophilous herbs were mainly dominated by Cyperaceae, Poaceae, Myriophyllum, Polygonum and Typha, and they gradually increased from 18.7 to 16.8 ka, suggesting a transition to a more humid climate. This corresponds to climate cooling over the same period. From 16.8 to 14.6 ka, hydrophilous herbs continued to increase, coincident with a general ameliorating trend indicated by δ18O records from East Asia. Between 14.6 and 14.0 ka, the mean content of hydrophilous herbs reached peak in the sequence, corresponding to relatively high δ18O values during this period. From ~14.0 to 12.9 ka, the abundance of hydrophilous herbs decreased significantly. Over the same period, the Greenland ice core shows a decrease in δ18O and low-latitude cave stalagmites in China record an increase in δ18O. This implies that longitudinal temperature gradients increased and drove the southward retreat of the ISM, which in turn drove a continuous decrease in the abundance of hydrophilous herbs in the study area. From 12.9 to 11.6 ka, the mean content of hydrophilous herbs decreased to the lowest (8.3%) in the whole sequence, indicating a cold and dry climate in the study area. A positive shift in δ18O records during 11.6–10.6 ka was matched by a significant increase in the abundance of hydrophilous herbs in the study area, indicating a warm and humid climate trending. Hence, the ISM has had a significant impact on the climate of the eastern TP since the onset of deglaciation around ~16.8 ka.
Highlights
The Cenozoic collision of the Indian and Asian plates resulted in uplift of the Tibetan Plateau (TP) and the formation of a steep eastern margin of the plateau, where the elevation decreases from >5000 m to ~600 m over a distance of ~50 km [Fig 1]
Longitudinal temperature gradients increased from 14.0 to 12.9 ka in the Northern Hemisphere and drove the southward retreat of the Indian Summer Monsoon (ISM) circulation. We propose that this resulted in a decrease in hydrophilous herbs from 14.0 to 12.9 ka [Fig 4A], accompanied by drought in the middle Yangtze region, with some fluctuations [Fig 4F]
Hydrophilous herbs showed a clear change which can be correlated with existing records
Summary
The Cenozoic collision of the Indian and Asian plates resulted in uplift of the Tibetan Plateau (TP) and the formation of a steep eastern margin of the plateau, where the elevation decreases from >5000 m to ~600 m over a distance of ~50 km [Fig 1] We investigate the well-dated Xinmocun lacustrine section to reveal the climatic conditions of the last deglaciation by analyzing variations in the pollen record. This record is correlated with other contemporary records from the eastern Asia, and the controlling mechanism of climate change during this period is addressed
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