Intra-annual variation of the calcite deposition rate of drip water in Shihua Cave, Beijing, China and its implications for palaeoclimatic reconstructions

Monthly in situ monitoring of the calcite deposition rate, drip-water chemistry and surrounding cave environment was carried out at Shihua Cave, Beijing, China, through two hydrological years (from January 2006 to February 2008) to determine the seasonal variability and mechanisms of stalagmite growth in Shihua Cave. Calcite deposition rates exhibit significant intra-annual variation, with the lowest values during the summer monsoonal rainy season (July-August) and peak values from autumn to spring. The temporal change in the calcite deposition rate is negatively correlated with the drip rate, cave-air PCO(2) (CO(2) partial pressure) and Ca concentration, and positively correlated with the pH of the feeding drip water. The seasonal recharge regime of drip water is likely to be the primary control on the drip-water quality and quantity, which, in turn, control the calcite deposition rate in Shihua Cave. During the summer rainy season, periodic and intense rainstorms increase the drip rate and cave-air PCO(2), leading to drip water with a lower pH and saturation index of calcite, thereby reducing the calcite precipitation. It seems that the high cave-air PCO(2) is the dominant control on the calcite deposition rate during the rainy season. Our previous study on the dissolved organic carbon of drip water concluded that the thin luminescent bands in stalagmite laminae from Shihua Cave form during the rainy season. The lower calcite deposition rate during the rainy season further supports this suggestion. The significant intra-seasonal variability of the calcite deposition rate implies that the seasonal bias of delta(18)O of stalagmites should be considered when stalagmite delta(18)O is used as a high-resolution palaeoclimatic archive.