CP Climate of the Past CP 1814-9332 Copernicus GmbH Göttingen, Germany 10.5194/cp-8-1781-2012 Simulated oxygen isotopes in cave drip water and speleothem calcite in European caves Wackerbarth A. 1 Langebroek P. M. 2 3 Werner M. 2 Lohmann G. 2 Riechelmann S. 4 Borsato A. 5 Mangini A. 1 Heidelberg Academy of Sciences, Heidelberg, Germany Alfred Wegener Institute, Bremerhaven, Germany Bjerknes Centre for Climate Research, Bergen, Norway Ruhr-Universität Bochum, Bochum, Germany Museo delle Scienze, Trento, Italy 05 11 2012 8 6 1781 1799 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past.net/8/1781/2012/cp-8-1781-2012.html The full text article is available as a PDF file from http://www.clim-past.net/8/1781/2012/cp-8-1781-2012.pdf

Interpreting stable oxygen isotope (&delta;<sup>18</sup>O) records from stalagmites is still one of the complex tasks in speleothem research. Here, we present a novel model-based approach, where we force a model describing the processes and modifications of &delta;<sup>18</sup>O from rain water to speleothem calcite (Oxygen isotope Drip water and Stalagmite Model – ODSM) with the results of a state-of-the-art atmospheric general circulation model enhanced by explicit isotope diagnostics (ECHAM5-wiso). The approach is neither climate nor cave-specific and allows an integrated assessment of the influence of different varying climate variables, e.g. temperature and precipitation amount, on the isotopic composition of drip water and speleothem calcite. <br><br> First, we apply and evaluate this new approach under present-day climate conditions using observational data from seven caves from different geographical regions in Europe. Each of these caves provides measured &delta;<sup>18</sup>O values of drip water and speleothem calcite to which we compare our simulated isotope values. For six of the seven caves modeled &delta;<sup>18</sup>O values of drip water and speleothem calcite are in good agreement with observed values. The mismatch of the remaining caves might be caused by the complexity of the cave system, beyond the parameterizations included in our cave model. <br><br> We then examine the response of the cave system to mid-Holocene (6000 yr before present, 6 ka) climate conditions by forcing the ODSM with ECHAM5-wiso results from 6 ka simulations. For a set of twelve European caves, we compare the modeled mid-Holocene-to-modern difference in speleothem calcite &delta;<sup>18</sup>O to available measurements. We show that the general European changes are simulated well. However, local discrepancies are found, and might be explained either by a too low model resolution, complex local soil-atmosphere interactions affecting evapotranspiration or by cave specific factors such as non-equilibrium fractionation processes. <br><br> The mid-Holocene experiment pronounces the potential of the presented approach to analyse &delta;<sup>18</sup>O variations on a spatially large (regional to global) scale. Modelled as well as measured European &delta;<sup>18</sup>O values of stalagmite samples suggest the presence of a strong, positive mode of the North Atlantic Oscillation at 6 ka before present, which is supported by the respective modelled climate parameters.

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