isotopic ratios for both elements. In zone ISO 1 (40-34 cm), the isotopic composition of the sediment shows steady values around -1.5 ‰ for δ18O and -1.2‰ for δ13C. Zone ISO 2 (34-29 cm) is characterized by lower isotopic compositions, δ18O less than -1.5 ‰ and δ13C mean values ~ 1.2‰, respectively. In zone ISO 3 (29-23 cm) values are higher than in ISO 1, reaching mean values of -1.3‰ for δ18O and -1.3‰ for δ13C . Zone ISO 4 (23-15 cm) is marked by a decrease of δ18O and δ13C, with mean values of -1.8‰ and -1.9‰, respectively. Zone ISO 5 (15-8 cm) has the most enriched isotopic compositions, reaching values around -0.4 ‰ for δ18O and 0.0‰ for δ13C. The upper part of the sediment core, zone ISO 6 (8-0 cm), is characterized by decreasing values from ISO 5 with minima at the surface. DISCUSSION The isotopic composition of lake waters are controlled by the hydrological balance between inputs (groundwater, direct precipitation, surface and stream inflows) and outputs (groundwater loss, evaporation, surface and stream outflows) (Leng et al., 2005). As a consequence different types of lake physiography mean that water isotopic composition can respond differently to the same forcing (Jonsson et al., 2009). As a closed lake in a karstic catchment, topographically isolated from fluvial inflows and outflows, regional influence of surface water can be excluded from Lagunillo’s mass balance. The surface waters of Lagunillo del Tejo plot below the Global Meteoric Water Line (GMWL; Fig. 2) indicating that evaporative processes control the lake's isotopic mass balance. The fundamental controls on the isotope signature in sediment are quite well understood and documented (e.g. Leng et al., 2005; Ito, 2001). In the specific case of sediment that shows a covariant trend between δ18O and δ13C, the isotopic signal can be used as a
Becker D., Picot L. and Berger J.P. (2002) Stable isotopes (δ13C and δ18O) of charophyte gyrogonites: example from the Brochene Fluh Section (Late Oligocene-Early Miocene, Switzerland). Geobios 35:89-97. Bullón Mata T. (2012) Avenidas fluviales y precipitaciones en las cuencas de los rios Jarama-Tajo al final del siglo XVI. Boletín de la Asociación de Geógrafos Españoles 60: 77-90. Craig H. (1961) Isotopic Variations in Meteoric Waters. Science 133:1702-1703. Currey D.R. (1990) Quaternary palaeolakes in the evolution of semidesert basins, with special emphasis on Lake Bonneville and the Great Basin, U.S.A. Palaeogeography, palaeoclimatology, palaeoecology 76:189-214. Dearing J.A. and Foster I.D.L. (1986) Lake sediments and palaeohydrological studies, in: Handbook of the Holocene Palaeoecology and Palaeohydrology (Wiley ed), pp 67-90. Deocampo D.M. (2011) The Geochemistry of continental carbonates, in: Carbonates in Continental Settings: geochemistry, diagenesis and applications Developments in Sedimentology (Alonso-Zarza AM and Tanner LH eds), pp 1-59, Elsevier. Domínguez-Castro F., Ramos A.R., García-Herrera R., and Trigo R.M., 2014. Iberian extreme precipitation 1855/1856: an analysis from early instrumental observations and documentary sources. International Journal of Climatology 35:142-153. Eastwood W.J., Leng M.J., Roberts N., and Davis B. (2007) Holocene climate change in the eastern Mediterranean region: a comparison of stable isotope and pollen data from Lake Gölhisar, southwest Turkey. Journal of quaternary science
López-Blanco C., Vicente E., and Miracle M.R. (2012b) Cladocera sub-fossils and plant macrofossils as indicators of droughts in Lagunillo del Tejo (Spain) – implications for climatic studies. Fundamental and applied limnology Machado M.J., Benito G., Barriendos M., and Rodrigo F.S. (2011) 500 Years of rainfall variability and extreme hydrological events in southeastern Spain drylands. Journal of arid environments 75:1244-1253. Magny M., Gauthier E., Vanniere B., and Peyron O. (2008) Palaeohydrological changes and human-impact history over the last millennium recorded at Lake Joux in the Jura Mountains, Switzerland. Holocene (Sevenoaks) 18:255-265. Miracle M.R., and Vicente E. (1983) Vertical distribution and rotifer concentrations in the chemocline of meromictic lakes. Hydrobiologia 104: 259-267. Miracle M.R., Vicente E., and Pedrós-Alió C. (1992) Biological studies of Spanish meromictic and stratified karstic lakes. Limnetica 8:59-77. Myrbo A. (2006) The lacustrine carbon cycle and its representation in lake sediments. University of Minnesota, Minnesota. Olcina Cantos, J. (1994) Riesgos climáticos en la Península Ibérica. Acción Divulgativa, Madrid. Pérez Cueva A.J. (1994) Atlas climàtic de la Comunitat Valenciana (1961–1990). Generalitat Valenciana, Valencia. Polsenaere P. and Abril G. (2012) Modelling CO2 degassing from small acidic rivers using water pCO2, DIC and delta 13C-DIC data. Geochimica Cosmochimica Acta 91: 220-239. Rivas-Martínez S. and Loidi J. (1999) Bioclimatology of the Iberian Peninsula. Itinera Geobotanica 13:41-48.