Holocene moisture variations across China and driving mechanisms: A synthesis of climatic records

Based on the review of 33 Holocene moisture reconstructions that passed quality scrutiny, temporal and spatial patterns of regional moisture variations are delineated. The regionally-averaged moisture index from Xinjiang demonstrates that the moisture index has been persistently climbing since ∼10 ka cal BP and that the period between ∼4 and ∼0 ka cal BP is the Holocene Moisture Optimum. Comparison of the moisture index of Xinjiang region with the winter climate of northern Europe leads us to propose that the Holocene moisture variations in Xinjiang region have been controlled by the winter temperature variations in the North Atlantic region. The regionally-averaged moisture index from the Tibetan Plateau shows that the moisture has been persistently declining since ∼11 ka cal BP and that the period between ∼11.5 and 7.5 ka cal BP was the Holocene Moisture Optimum. The parallel trends between the moisture level in the Tibetan Plateau and the Indian summer monsoon strength retrieved from the Arabian Sea suggest that the Tibetan Plateau has been under influence of the Indian summer monsoon throughout the Holocene. The regionally-averaged moisture index curves from Northern China and Southern China are the delayed reflections of the East Asian summer monsoon strength to the solar radiation. That is, the peak insolation was responded by the Holocene “Oceanic Thermal Optimum” with significant time lags and the “Oceanic Thermal Optimum” was then responded by the “Holocene Moisture Optimum” in southern China and northern China also with some time lags. The differences in the moisture-index curve shapes and in the durations of the “Holocene Moisture Optimum” between northern China and southern China suggest that the strength of the East Asian summer monsoon had gradually transgressed northward in the early Holocene and gradually regressed southward in the late Holocene.