DRIP-WATER HYDROLOGY, GEOCHEMISTRY AND FLUORESCENCE AT STUMP CROSS CAVERNS, YORKSHIRE, ENGLAND

Stump Cross Caverns is an upland cave situated in a high fractured outlier of Carboniferous limestone in central England. The site is overlain by both thin peats and gley soils, with a heather-bog-upland grass vegetation, with limited sheep grazing and also some reforestation. Rainfall occurs all year with little seasonal variability, and mean annual temperature is ~7 °C. This research aims to make a long term (4 years to date) integrated study of drip water hydrology, geochemistry and fluorescence at the site, with emphasis on stalagmite forming drip waters where the stalagmites might be later used for palaeoclimate analysis. Five sensors have been deployed in the caverns since 1998 at drip sites that have a wide range of discharges. Each of the monitored drips has a different response to surface climate. As expected, sites with a higher mean drip rate have a greater drip variability and a more rapid response to surface rainfall. More surprisingly, two sites show a non-linear response, with very rapid increases in dripping after some high rainfall events, for one drip this is despite a relatively low drip rate. Geochemical results were obtained from both one-off samples throughout the cave as well as high frequency temporal sampling of four drip sources at or adjacent to the logger sites. Results demonstrate a mean calcium concentration of 50-110 ppm, with a spatial variability similar to seasonal variability. Strontium shows a strong seasonal trend, with high Sr at low drip rates. Fluorescence results show that fluorescence wavelength varies between sites both seasonally and over longer time trends. Sites that are adjacent have similar evolution through time, with drip waters above the grazed moorland having a different trend than the other sites. Overall it is observed that (1) Slower drip sites are less variable and more lagged as expected, with non-linear drip responses to surface rainfall occurring but possibly confined to one section of the cave due to local hydrology. (2) Geochemistry suggests that the Strontium - drip rate relationship has significant potential, and that it could be used in stalagmites to reconstruct past drip rates. (3) Fluorescence data suggests that this signal, at least today, is locally variable due to human impacts.