Moisture-advection feedback supports strong early-to-mid Holocene monsoon climate on the eastern Tibetan Plateau as inferred from a pollen-based reconstruction
2014
Herzschuh, Ulrike | Borkowski, Janett | Schewe, Jacob | Mischke, Steffen | Tian, Fang
(Paleo-)climatologists are challenged to identify mechanisms that cause the observed abrupt Holocene monsoon events despite the fact that monsoonal circulation is assumed to be driven by gradual insolation changes. Here we provide proxy and model evidence to show that moisture-advection feedback can lead to a non-linear relationship between sea-surface and continental temperatures and monsoonal precipitation. A pollen record from Lake Ximencuo (Nianbaoyeze Mountains) indicates that vegetation from the eastern margin of the Tibetan Plateau was characterized by alpine deserts and glacial flora after the Last Glacial Maximum (LGM) (21–15.5calkyr BP), by alpine meadows during the Late Glacial (15.5–10.4calkyr BP) and second half of the Holocene (5.0cal kyr BP to present) and by mixed forests during the first half of the Holocene (10.4–5.0calkyr BP). The application of pollen-based transfer functions yields an abrupt temperature increase at 10.4calkyr BP and a decrease at 5.0calkyr BP of about 3°C. By applying endmember modeling to grain-size data from the same sediment core we infer that frequent fluvial events (probably originating from high-magnitude precipitation events) were more common in the early and mid Holocene. We assign the inferred exceptional strong monsoonal circulation to the initiation of moisture-advection feedback, a result supported by a simple model that reproduces this feedback pattern over the same time period.
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