Moisture - advection feedback supports strong early - to - mid Holocene monsoon 1 climate on the eastern Tibetan Plateau as inferred from a pollen - based 2 reconstruction 3 4

32 (Paleo-)climatologists are challenged to identify mechanisms that cause the 33 observed abrupt Holocene monsoon events despite the fact that monsoonal 34 circulation is assumed to be driven by gradual insolation changes. Here we provide 35 proxy and model evidence to show that moisture-advection feedback can lead to a 36 non-linear relationship between sea-surface and continental temperatures and 37 monsoonal precipitation. A pollen record from Lake Ximencuo (Nianbaoyeze 38 Mountains) indicates that vegetation from the eastern margin of the Tibetan Plateau 39 was characterized by alpine deserts and glacial flora after the Last Glacial Maximum 40 (LGM) (21–15.5 cal kyr BP), by alpine meadows during the Late Glacial (15.5–10.4 41 cal kyr BP) and second half of the Holocene (5.0 cal kyr BP to present) and by mixed 42 forests during the first half of the Holocene (10.4-5.0 cal kyr BP). The application of 43 pollen-based transfer functions yields an abrupt temperature increase at 10.4 cal kyr 44 BP and a decrease at 5.0 cal kyr BP of about 3°C. By applying endmember modeling 45 to grain-size data from the same sediment core we infer that frequent fluvial events 46 (probably originating from high-magnitude precipitation events) were more common 47 in the early and mid Holocene. We assign the inferred exceptional strong monsoonal 48 circulation to the initiation of moisture-advection feedback, a result supported by a 49 simple model that reproduces this feedback pattern over the same time period. 50