A reconstruction of Holocene rainfall is presented for southwest China - an area prone to drought and flooding due to variability in the East Asian monsoon. The reconstruction is derived by comparing a new high-resolution stalagmite δ18O record with an existing record from the same moisture transport pathway. The new record is from Heshang Cave (30°27′N, 110°25′E; 294 m) and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature. Heshang lies 600 km downwind from Dongge Cave which has a published high-resolution δ18O record (Wang, Y.J., Cheng, H., Edwards, R.L., He, Y.Q., Kong, X.G., An, Z.S., Wu, J.Y., Kelly, M.J., Dykoski, C.A., Li, X.D., 2005. The Holocene Asian monsoon: links to solar changes and North Atlantic climate. Science 308, 854-857). By differencing co-eval δ18O values for the two caves, secondary controls on δ18O (e.g. moisture source, moisture transport, non-local rainfall, temperature) are circumvented and the resulting Δδ18O signal is controlled directly by the amount of rain falling between the two sites. This is confirmed by comparison with rainfall data from the instrumental record, which also allows a calibration of the Δδ18O proxy. The calibrated Δδ18O record provides a quantitative history of rainfall in southwest China which demonstrates that rainfall was 8% higher than today during the Holocene climatic optimum (≈ 6 ka), but only 3% higher during the early Holocene. Significant multi-centennial variability also occurred, with notable dry periods at 8.2 ka, 4.8-4.1 ka, 3.7-3.1 ka, 1.4-1.0 ka and during the Little Ice Age. This Holocene rainfall record provides a good target with which to test climate models. The approach used here, of combining stalagmite records from more than one location, will also allow quantification of rainfall patterns for past times in other regions. © 2008

Extreme hydrologic events such as storms and floods have the potential to severely impact modern human society. However, the frequency of storms and their underlying mechanisms are limited by a paucity of suitable proxies, especially in inland areas. Here we present a record of speleothem magnetic minerals to reconstruct paleoprecipitation, including storms, in the eastern Asian monsoon area over the last 8.6 ky. The geophysical parameter IRM_soft-flux represents the flux of soil-derived magnetic minerals preserved in stalagmite HS4, which we correlate with rainfall amount and intensity. IRM_soft-flux exhibits relatively higher values before 6.7 ky and after 3.4 ky and lower values in the intervening period, consistent with regional hydrological changes observed in independent records. Abrupt enhancements in the flux of pedogenic magnetite in the stalagmite agree well with the timing of known regional paleofloods and with equatorial El Niño−Southern Oscillation (ENSO) patterns, documenting the occurrence of ENSO-related storms in the Holocene. Spectral power analyses reveal that the storms occur on a significant 500-y cycle, coincident with periodic solar activity and ENSO variance, showing that reinforced (subdued) storms in central China correspond to reduced (increased) solar activity and amplified (damped) ENSO. Thus, the magnetic minerals in speleothem HS4 preserve a record of the cyclic storms controlled by the coupled atmosphere−oceanic circulation driven by solar activity.

Modern precipitation variability over East China is known to be characterized by meridional tripole and dipole structures, linked to atmosphere and ocean dynamics. As the instrumental data may be influenced by anthropogenic global warming, it is unclear whether the physical mechanism underlying the tripole and dipole pattern have remained constant since the pre-industrial period. Here we investigate spatiotemporal precipitation variability over the past 1150 years using three high-resolution stalagmite δ¹⁸O records from southern, central and northern China. Principal component analysis results suggest that the first principal component, reflecting large-scale Asian monsoon strength, is closely linked to solar variability. The second and third principal components, which reflect rainfall, reveal tripole and dipole patterns that persist over the last millennium and are driven by the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). We find that interactions between the monsoon, PDO, and AMO influence spatiotemporal rainfall patterns in East China.

Heshang Cave is situated in central China (30°27’N, 110°25’E; 294 m) in the middle reaches of the Yangtze Valley, a region strongly impacted by the East Asian Monsoon. It contains large annually-laminated Holocene and late Pleistocene stalagmites which capture past monsoon behaviour with seasonal resolution, and could enhance understanding of the amplitude and frequency of monsoon behaviour in different climate states. In this paper, we present results of a 3-year monitoring programme at Heshang. T loggers outside the cave agree closely with T data from nearby meteorological stations. T at the site of growth of the largest recovered stalagmite averages 18°C (identical to mean annual T outside the cave) with a seasonal amplitude of 5ºC (about one fifth of the external cycle). Rainfall measurements from a station 3 km from the cave indicate strong summer monsoon rain in 2004 and 2005, but rather weaker summer rain (by ≈30%) in 2006. Drip rate at the monitoring site has a base flow of 14 drips/minute and shows a sharp increase to ≈40 drips/minute early in the summer rains of 2004 and 2005, followed by a gradual return to base-flow as the monsoon weakens. This abrupt change presumably represents threshold behaviour in the hydrological system. This threshold is not passed in 2006 and there is no abrupt increase in drip rate, indicating the sensitivity of this site (and presumably of speleothem chemistry in this cave) to monsoon rainfall. Results are also reported from a 10-month deployment of a Stalagmate drip counter, and for CO2 levels in Heshang Cave. Overall, this monitoring work represents an essential dataset for interpretation of the chemistry of drip waters, of carbonates grown on glass slides and, ultimately, of long speleothem records of past climate from Heshang Cave.