Search

Terrestrial palaeo-temperature data are of great value in improving our understanding of past climate and they provide a basis for evaluating climate simulations. Such data are, however, poorly constrained for long time-scales. In addition to the scarcity of high-quality continuous time-series, finding proxies with a clear response to past temperature changes and developing appropriate reconstruction methods are major challenges. We present a new and robust method – Locally-weighted Weighted-average partial least squares (LW-WAPLS) to reconstruct quantitative temperature changes based on a high-resolution 1.74-Ma pollen record from the Zoige Basin on the eastern Tibetan Plateau, where the vegetation today is mainly controlled by temperature. The reconstructed mean annual (MAT) and warmest month (MTWM) temperatures reveal a general cooling trend with two major shifts at ~1.54 and 0.62 Ma BP, and regular glacial-interglacial variability ranging from ~ − 4 to 2 °C and from 8 to 16 °C, respectively. They indicate ~4–5 °C (MAT) and ~ 5–6 °C (MTWM) magnitudes of glacial-interglacial temperatures. Both statistical and ecological evaluations validate the reliability of the reconstructions. The reconstructions provide important insights into the spatial aspects of long-term terrestrial temperature change. LW-WAPLS shows advantages over both the traditional modern analogue technique and non-linear transfer-function methodologies such as WAPLS for reconstructing the broad-scale climate changes for the Zoige Basin, by combining the strength of both methods. The LW-WAPLS approach potentially provides a robust tool to develop pollen-based climate reconstructions over long time-scales. • LW-WAPLS approach is a powerful tool for the quantitative reconstructions of climate on glacial-interglacial scales. • Temperature reconstructions of the eastern Tibetan Plateau reveal the stepwise cooling trend with two major shifts at 1.54 and 0.62 Ma BP and with ~4-5oC (MAT) and 5-6oC (MTWM) magnitude. • Our long-term temperature reconstruction fills a data gap in mid-latitude terrestrial regions • The results provide valuable data for model simulations to elucidate the climate mechanisms [ABSTRACT FROM AUTHOR]

Existing pollen records reveal that a shift from tree-rich to herb-dominated vegetation occurred on the eastern Tibetan Plateau (TP) during the mid-to-late Holocene, which gave rise to the modern vegetation pattern. However, given the complex climatic regulation of vegetation growth, the main climatic controls on arboreal vegetation in the eastern TP still need to be explored. In this study, a 387.5 cm sediment core covering the last 12.6 cal ka was recovered from Emu Co on the eastern TP. Based on pollen analysis in conjunction with the modern analogue technique, the role of various climate factors influencing past vegetation changes was modelled. Our results show that, during 12.6–9.5 cal ka BP, the study area experienced an arid and cold climate, with a sparse vegetation cover, as evidenced by the high abundance of herbaceous pollen and low total pollen concentration. A cold-tolerant deciduous broadleaved arboreal component, dominated by Betula , began to expand at ca. 9.5 cal ka BP, replacing herbaceous vegetation habitat, suggesting a gradual warming and wetting trend. Controlled mainly by rising temperatures, evergreen coniferous tree components develop from 8.7 to 5 cal ka BP, with Picea pollen reaching its maximum abundance. After 5 cal ka BP, the herbaceous vegetation re-expands under the combined pressure of lower temperatures and reduced precipitation. Declining arboreal pollen abundance in the mid-to-late Holocene is prevalent in the available fossil pollen records, but the main drivers have regional peculiarities: in the east-central region of the TP near Emu Co, lower temperatures may have played a more important role in the retreat of trees than reduced precipitation. Conversely, arboreal retreat and vegetation change in the north-east and south-east regions may be related to the weakening of the Asian summer monsoon circulation and seasonal climate changes caused by the East Asian winter monsoon and Indian summer monsoon, respectively. • A Holocene pollen record from the forest/meadow ecotone on the Tibetan Plateau. • Arboreal pollen reduces strongly at ca. 5 cal ka BP on the eastern Tibetan Plateau. • The importance of temperature and precipitation for arboreal decline varies by region. [ABSTRACT FROM AUTHOR]