The Tibetan Plateau exerts a major influence on Asian climate, but its long-term environmental history remains largely unknown. We present a detailed record of vegetation and climate changes over the past 1.74 million years in a lake sediment core from the Zoige Basin, eastern Tibetan Plateau. Results show three intervals with different orbital- and millennial-scale features superimposed on a stepwise long-term cooling trend. The interval of 1.74–1.54 million years ago is characterized by an insolation-dominated mode with strong ~20,000-year cyclicity and quasi-absent millennial-scale signal. The interval of 1.54–0.62 million years ago represents a transitional insolation-ice mode marked by ~20,000- and ~40,000-year cycles, with superimposed millennial-scale oscillations. The past 620,000 years are characterized by an ice-driven mode with 100,000-year cyclicity and less frequent millennial-scale variability. A pronounced transition occurred 620,000 years ago, as glacial cycles intensified. These new findings reveal how the interaction of low-latitude insolation and high-latitude ice-volume forcing shaped the evolution of the Tibetan Plateau climate.

A promising method of reconstructing palaeovegetation from pollen records uses 18 mathematical models of the relationship between pollen and vegetation, which can be 19 calibrated using the Extended R-Value (ERV) approach on datasets of modern pollen 20 assemblages and related vegetation survey data. This study presents the results of 21 calibrating the models for non-arboreal pollen types in alpine meadow habitats on the 22 Tibetan Plateau. 23Pollen assemblages from surface soil samples and surrounding vegetation data 24 were collected for 30 randomly located sites in the Zoige Basin, northeastern Tibetan 25 Plateau. ERV analysis found that the most reliable results were obtained when using 26 ERV sub-models 1 and 2 and distance-weighting the vegetation data by applying the 27 taxon-specific Prentice-Sutton method. 28The relevant source area of pollen (RSAP) for soil samples in alpine meadows of 29 the northeastern Tibetan Plateau is ca. 200 m. Relative pollen productivities (RPPs) of 30 15 non-arboreal taxa were estimated relative to Cyperaceae (RPPCyp). The taxa can be 31 divided into 3 groups according to their RPPs, those with high RPPCyp (> 1.68: 32