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East Asian summer monsoon (EASM) rainfall impacts the world’s most populous regions. Accurate EASM rainfall prediction necessitates robust paleoclimate reconstructions from proxy data and quantitative linkage to modern climatic conditions. Many precisely dated oxygen isotope records from Chinese stalagmites have been interpreted as directly reflecting past EASM rainfall amount variability, but recent research suggests that such records instead integrate multiple hydroclimatic processes. Using a Lagrangian precipitation moisture source diagnostic, we demonstrate that EASM rainfall is primarily derived from the Indian Ocean. Conversely, Pacific Ocean moisture export peaks during winter, and the moisture uptake area does not differ significantly between summer and winter and is thus a minor contributor to monsoonal precipitation. Our results are substantiated by an accurate reproduction of summer and winter spatial rainfall distributions across China. We also correlate modern EASM rainfall oxygen isotope ratios with instrumental rainfall amount and our moisture source data. This analysis reveals that the strength of the source effect is geographically variable, and differences in atmospheric moisture transport may significantly impact the isotopic signature of EASM rainfall at the Hulu, Dongge, and Wanxiang Cave sites. These results improve our ability to isolate the rainfall amount signal in paleomonsoon reconstructions and indicate that precipitation across central and eastern China will directly respond to variability in Indian Ocean moisture supply.

A record from Wanxiang Cave, China, characterizes Asian Monsoon (AM) history over the past 1810 years. The summer monsoon correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes. It was generally strong during Europe's Medieval Warm Period and weak during Europe's Little Ice Age, as well as during the final decades of the Tang, Yuan, and Ming Dynasties, all times that were characterized by popular unrest. It was strong during the first several decades of the Northern Song Dynasty, a period of increased rice cultivation and dramatic population increase. The sign of the correlation between the AM and temperature switches around 1960, suggesting that anthropogenic forcing superseded natural forcing as the major driver of AM changes in the late 20th century.

Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave, Wudu, Gansu, variation of monsoonal precipitation in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed. Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves, suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation, controlled by “amount effect” of the precipitation. Variation of the monsoonal precipitation during the past 100 years can be divided into three stages, increasing from AD 1875 to 1900, then decreasing from AD 1901 to 1946, and increasing again thereafter. This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents. This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977, with higher monsoonal precipitation corresponding to cold PDO phase and vice versa at decadal timescale. The monsoonal precipitation variation is out of phase with the PDO after AD 1977, probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77. These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction. This relationship will aid to forecast future hydrological cycle for the AM monsoon region, and to improve forecasting potential of climatic model with observation data from cave.

Speleothems from Wanxiang Cave, China (33°19′ N, 105°00′ E), located near the northern limit of the East Asian summer monsoon, provide high-resolution records of paleomonsoon variability. We present a simple model for interpreting δ18O shifts in speleothems from this region in which the δ18O of speleothem calcite is inversely related to monsoon intensity. In contrast to observations at higher latitudes, atmospheric temperature has little effect on δ18O of precipitation near Wanxiang Cave. Furthermore, the temperature dependence of calcite-water δ18O fractionation acts in the opposite sense, most likely canceling out the effect of local temperature variations on speleothem δ18O. Given this, the maximum δ18O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5‰. Accordingly, it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7‰ range observed in fossil Wanxiang Cave speleothems. Two stalagmites, WXSM 51 and WXSM 52, exhibit more positive δ18O during stadial periods (marine isotope stages [MIS] 8, 6, 5d, 5b, and 2) than during interstadial periods (MIS 9, 5a, 5c, 5e). Thus, East Asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods. We present detailed δ18O records from MIS 5a-5b and 5c-5d. During the MIS 5d-5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b-5a transition, monsoon intensity increased abruptly at about 85.7 ka, when δ18O decreased by approximately 4‰ in 200 years. Monsoon variability, inferred from the MIS 5c-5d and MIS 5a-5b records, closely coincides with global climate changes observed in the GISP2, Vostok, and SPECMAP records, and with the Northern Hemisphere insolation curve. This suggests that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in Northern Hemisphere incident solar radiation. The MIS 5a-5b and 5c-5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that δ18O of speleothems from Wanxiang Cave is a valid proxy for past changes in monsoon intensity. © 2006 Elsevier B.V. All rights reserved.

Abstract: Speleothems from Wanxiang Cave, China (33°19′ N, 105°00′ E), located near the northern limit of the East Asian summer monsoon, provide high-resolution records of paleomonsoon variability. We present a simple model for interpreting δ 18O shifts in speleothems from this region in which the δ 18O of speleothem calcite is inversely related to monsoon intensity. In contrast to observations at higher latitudes, atmospheric temperature has little effect on δ 18O of precipitation near Wanxiang Cave. Furthermore, the temperature dependence of calcite–water δ 18O fractionation acts in the opposite sense, most likely canceling out the effect of local temperature variations on speleothem δ 18O. Given this, the maximum δ 18O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5‰. Accordingly, it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7‰ range observed in fossil Wanxiang Cave speleothems. Two stalagmites, WXSM 51 and WXSM 52, exhibit more positive δ 18O during stadial periods (marine isotope stages [MIS] 8, 6, 5d, 5b, and 2) than during interstadial periods (MIS 9, 5a, 5c, 5e). Thus, East Asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods. We present detailed δ 18O records from MIS 5a–5b and 5c–5d. During the MIS 5d–5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b–5a transition, monsoon intensity increased abruptly at about 85.7 ka, when δ 18O decreased by approximately 4‰ in 200 years. Monsoon variability, inferred from the MIS 5c–5d and MIS 5a–5b records, closely coincides with global climate changes observed in the GISP2, Vostok, and SPECMAP records, and with the Northern Hemisphere insolation curve. This suggests that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in Northern Hemisphere incident solar radiation. The MIS 5a–5b and 5c–5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that δ 18O of speleothems from Wanxiang Cave is a valid proxy for past changes in monsoon intensity. [Copyright &y& Elsevier]