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Abstract:
In order to better understand the organic content of microbands in speleothems, seasonal variations in the organic concentrations of vadose drip waters were examined in relation to climatic and environmental variables. Seasonal variations in the organic concentrations of the vadose waters were observed by documenting the fluctuations of Dissolved Organic Carbon (DOC) and its corresponding fluorescence. Tracer dye tests established that the larger drips depositing calcite in Marengo Cave were fed by waters with a short residence time. A strong seasonal variation in DOC concentrations and natural fluorescence was detected at quickly responding sites. Slow, constant drip sites displayed a weaker seasonality. Further investigation is required to distinguish low fluorescing DOC and to determine if the same fluorophors identified in the vadose water can be identified in the organics trapped in the recipient calcite. The overall conclusions are that fluorescence is well correlated with DOC when the fluorescence range is high but it is not a strong indicator of DOC at low fluorescence values; that the value of fluorescence as a predictor of DOC may vary significantly with individual sampling sites; and that the highest fluorescence values occur in springtime and the weakest in summer and fall.