INTRA- AND INTER-ANNUAL GROWTH RATE OF MODERN STALAGMITES

Abstract

We measure the factors that determine growth rate (temperature, drip rate, calcium ion concentration) for 31 waters that feed stalagmites within six cave systems throughout Europe. Water samples were collected at a frequency of at least 1 month, to permit the modelling of both inter- and intra-annual growth rate variations, utilising the theory of Wolfgang Dreybrodt (Chem. Geol. 29 (1980) 89-105; Chem. Geol. 32 (1981) 237-245; Dreybrodt, W., 1988. Processes in Karst Systems. Springer-Verlag, Berlin 288 pp.). Inter-annual growth rates were measured using the stalagmites that were associated with the analysed water samples; growth rate was determined from annual lamina counting, specific time markers within the stalagmites, and location of bomb 14C. When compared to theoretically predicted values, a good agreement between theoretical and measured stalagmite growth rates is observed (R2=0.69). When compared to site climate and geochemical parameters, a good correlation is observed between measured growth rate and mean annual temperature for five sites (R2=0.63) and dripwater calcium content (R2=0.61), but not drip rate (R2=0.09). The good correlation with both calcium and temperature is due to soil CO2 production being primarily determined by surface temperature and soil moisture. However, when we compare our data to that in the Grotte de Clamouse, a site that has little soil cover, we observe that the growth rate-temperature relationship breaks down due to either the lack of soil CO2 production or prior calcite precipitation. Intra-annual data demonstrates that maximum growth rate occurs when calcium concentrations are high, and that this occurs under different seasons depending on the hydrology of each site. Our results demonstrate a stronger dependence of intra-annual stalagmite growth rate on dissolved calcium ion concentrations than drip rate for the range of drip rates investigated here (0.01<t<2drip s-1), but for lower drip rates, this factor becomes important in controlling growth rate. We suggest that for well-monitored and -understood sites, stalagmite growth rate variations can provide useful information for palaeoclimate reconstruction.