Hydrological uncertainties in the modelling of cave drip-water δ18O and the implications for stalagmite palaeoclimate reconstructions

In this paper we review our current understanding of karst drip-water hydrology, emphasising the extent of non-linear and non-stationary process dynamics that render stalagmite palaeoclimate reconstructions using a statistical pseudo-proxy approach difficult to implement. We outline an approach to attribute the uncertainty that arises specifically as a consequence of variable water routing through the overlying soil, epikarst and karst aquifer. This is based upon the development of a monthly lumped parameter karst hydrological model which we use to demonstrate the range of modelled drip-water discharges possible from a single climate input. Refinement of the model, to include precipitation delta O-18, enables us to determine the theoretical range in drip-water and stalagmite delta O-18 for three sites with contrasting climates: northern temperate (NW Scotland), monsoonal (Ethiopia), and Mediterranean (Gibraltar). For actual climate (monthly mean temperature; monthly total precipitation; monthly mean precipitation delta O-18), we compare model simulations of karst groundwater storage and drip-water delta O-18 to demonstrate our ability to model different climate regimes realistically. We also investigate the delta O-18 variability associated with specific karst water reservoirs that differ in their capacity and drainage mechanisms. delta O-18 variability is then compared to stalagmite delta O-18 record from the three regions for the last similar to 45 years. We conclude by reviewing the implications of our hydrological model for stalagmite delta O-18 Quaternary palaeoclimate reconstructions over different timescales and sampling resolutions. (C) 2010 Elsevier Ltd. All rights reserved.