Seasonal variations and environmental controls on stalagmite calcite crystal growth in Heshang Cave, central China.

Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment. However, how exactly growth rates are affected by climate and environment is still unclear. We launched a monitoring and modeling program that lasted approximately 4 years on two active drip sites in Heshang Cave, central China. We collected comprehensive quantitative data on growth rates, cave temperature, CO₂ concentration, drip rate and drip-water chemistry to better understand the relationship between stalagmite growth and cave environment. By laying out glass substrates, we successfully grew stalagmite calcite crystals with rhombic characteristics, and quantified growth rates by measuring the long and short axes of calcite crystals under a microscope. Combined with coeval environmental data, we explicitly examined the roles of cave temperature, drip rate and drip-water chemistry in controlling the micro-scale growth of stalagmite calcite. Results show that growth of stalagmite calcite crystals at two drip sites exhibited similar seasonal variations -- generally faster in the summer months, at ~3 µm d^-1, and slower during the late winter to early spring, at ~1.5 µm d^-1. Variations in calcite growth rates were mainly determined by changes in cave temperature, with the growth rate increasing by 8.1%/°C and 6.6%/°C at the two locations. This indicates the potential use of stalagmite growth rates as a seasonal-resolution paleo-temperature proxy in some ventilated caves. On the other hand, the effect of drip rate and drip-water Ca²⁺ and SIC values on growth rates were not significant. [ABSTRACT FROM AUTHOR]