Report of a three-year monitoring programme at Heshang Cave, Central China

Abstract

Heshang Cave is situated in central China (30º27'N, 110º25'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 18ºC (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 CO 2 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. February 2008 influences. High rainfall during strong monsoon years can lead to severe flooding, so prediction of the onset and strength of the monsoon is an important goal to aid in planning for agriculture and water resources. These scientific and societal goals amply justify the study of speleothem records from Central China and have motivated extensive work on a variety of Chinese caves in recent years (e.g. Wang et al., 2001 Wang et al., 2005 Hu et al., 2008). KeywordsHeshang (meaning "monk" in Mandarin Chinese) was first visited for scientific purposes in the late 1990s, and speleothem samples first recovered in 1998. Early work on these samples demonstrated the potential of the cave for reconstruction of the past East Asian monsoon at very high resolution for at least the last 20 kyr. Publications on the cave have, to date, established the chronology of two speleothems (Hu et al., 2005; 2008), investigated the use of dissolved Si as a paleo-proxy in speleothems (Hu et al., 2005), established a quantitative Holocene record of rainfall in Central China (Hu et al., 2008), and investigated the reconstruction of past climate at seasonal resolution using Heshang speleothems (Johnson et al., 2006).

Radiocarbon evidence for decomposition of aged organic matter in the vadose zone as the main source of speleothem carbon

“…One expedition to the recharge zone in August 2004 described the soil at the recharge zone as 30 cm deep with reasonably dense vegetation (Hu et al, 2008a), which is consistent with the site at which sampling was conducted. Soil was collected from a site near the cave entrance during the field trip in March 2010 in 5 cm depth intervals until the bedrock was reached.…”

“…Speleothem calcite for the twentieth century record of a 14 C was drilled parallel to growth lamina as powder using a New Wave Research micromill. The age model for the twentieth century is based on annual layer counting described in Hu et al (2008a).…”

Links between the East Asian monsoon and North Atlantic climate during the 8,200 year event

“…These features allow reconstruction of the Asian monsoon at comparable resolution and temporal accuracy as observations in the Greenland ice cores. Heshang Cave has also been extensively monitored 16 so that the nature of the geochemical response to changing conditions is well understood 17 . Further details of the cave and the stalagmite used for this study (HS-4) are provided in the Supplementary Information.…”

Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling

“…Heshang cave is clearly more open and better ventilated than Dongge cave leading to greater heat and moisture exchange between the inside and outside cave (Hu et al, 2008b). During similar dry conditions, the evaporation effects in Heshang cave are expected to be more significant than in Dongge Cave, and the drier the condition, the heavier HS4 δ 18 O values expected, leading to lower or even negative δ 18 O values between DA and HS4.…”

“…Dongge is a cave consisting of branches with twists and turns, while Heshang is a much simpler cave with a nearly straight main passage, and a 20 m high entrance (Hu et al, 2008b). Heshang cave is clearly more open and better ventilated than Dongge cave leading to greater heat and moisture exchange between the inside and outside cave (Hu et al, 2008b).…”