Holocene climate change and landscape responses on the Tibetan Plateau: a comprehensive review

Glaciers on the Tibetan Plateau (TP) form the largest body of ice outsides of polar regions and are the sources of water for most major Asian rivers. Climate change and associated landscape responses over the TP have been widely investigated in past decades. However, the overall patterns of Holocene climate change and landscape responses remain unclear due to the complex atmospheric circulation over the Plateau and conflicts among various geologic records in different archives. Here we present a state of art review on records of climate change (temperature, precipitation) and responses of various landscape (glacier, lake level, aeolian deposit, vegetation etc) in order to obtain a comprehensive understanding of Holocene climate change and landscape responses over the TP. We reconstructed temperature variation based on available records of pollen assemblages, biomarkers and ice core oxygen isotopes, which shows a general cooling trend since the early Holocene and is apparently driven by summer insolation. The reconstructed precipitation based on pollen assemblages gradually increased throughout the Holocene, inconsistent with observation of both Indian and East Asian monsoon variation, suggesting either complex mechanism for precipitation changes on the TP or factors other than rainfall influencing pollen assemblages. Landscape response to climate change, e.g. increasing evidence of glacier advance since the Mid-Holocene and expansion of alpine meadow since the Early Holocene, appear to be influenced by a combination of temperature and precipitation variation throughout the Holocene. We also observed a moisture dipole based on composite evidence of lake level, aeolian sand and loess, which is supported by GCM modelling showing dipole under the interactions of the mid-latitude Westerlies and Asian Summer Monsoon.