Understanding conditions behind speleothem formation in Korallgrottan, northwestern Sweden

Abstract

In this study we investigate and characterise the environmental factors that control active speleothem growth in Korallgrottan, northwestern Sweden, in order to get a better understanding of seepage processes in karst areas and to determine whether the fossil speleothems from this site are suitable as palaeoclimatic archives. The drip rates from fast-dripping stalactites (>100 ml/day) vary substantially with the season and the snow regime. Comparisons with measurements of river discharge and simulated ground water recharge show that the drip rate from fast-dripping stalactites can be used as an estimation of the weekly to monthly ground water recharge. Slow-dripping stalactites however, have a steadier drip rate, with almost no seasonal variations. The δ 18 O composition of the drip water from both fast- and slow-dripping stalactites show some seasonal variation (±1.2‰), but is fairly stable compared to outside precipitation (±11.1‰). The δ 18 O signal from fast-dripping stalactites is biased towards summer conditions, while the signal is dampened at slow-dripping sites and an annual or even longer signal is evident. This holds true even though calcite precipitation may not occur continuously throughout the year. Similarly, the trace elemental composition of drip water is more stable in the slow-dripping stalactites, reflecting mean annual values or longer. Generally the drip water reaches the highest saturation level during the summer and autumn when biological activity in the soil zone is most intense, and the partial pressure of carbon dioxide, which controls limestone dissolution, is high.