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Abstract:
In the last decades speleothems have been established as a robust palaeoclimate archive using the U-disequilibrium dating method to construct accurate age-depth models. Advantages in dating methods and high spatial resolution of proxy measurements promote speleothems as an important palaeoclimate archive in high temporal resolution. Proxies such as stable isotopes (δ13C, δ18O) and trace elements can provide new insights into palaeoclimatological changes and changes in vegetation and soil. In addition to other palaeoclimate archives, speleothems occur worldwide in carbonate host rocks can add important information to local and regional palaeoclimate. Several precise 230Th/U-datings on Cueva Victoria speleothems were performed using a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). In addition, samples for stable carbon and oxygen isotopes (δ13C, δ18O) were micro milled with high spatial resolution using an isotope ratio mass spectrometer (IRMS). Laser ablation (LA)-ICP-MS technique was used to perform trace element measurements in very high spatial resolution. South-eastern Spain is one of the driest regions in Europe and high temporal resolution palaeoclimate archives are absent in this region, although they could provide important new information on hydrological changes from glacials to interglacials. 230Th/U-dating of Cueva Victoria speleothems shows preferred growth phases during interglacial phases. This indicates more humid conditions in combination with higher temperatures and is also displayed by more negative δ18O values in speleothems. These δ18O values are mainly influenced by temperature, amount effect and the source for rainwater, the proximate sea. Another important speleothem proxy is the carbon isotope composition (δ13C) reflecting vegetation type and microbiological soil activity above the cave. Concordant with δ18O values, δ13C values are more negative within warm phases as a result of a vegetation increase. However, during the Holocene, elevated δ13C values indicate less favourable conditions for the vegetation. High summer insolation during the Holocene (9.7 - 7.8 ka) enhances seasonality and, as a result, summer drought is prolonged and extended to the growing season in springtime, which is in agreement to other Mediterranean palaeoclimate archives. Since the end of the last interglacial during Marine Isotope Stages 5 to 3, climate is strongly influenced by millennial Northern Hemisphere temperature changes by the warm Dansgaard/Oeschger (DO) and cool Heinrich events. Warm DO events are accompanied by humid conditions and an increase in vegetation density, which is reflected by very negative speleothem δ13C and δ18O values. Cold phases, however, show less negative speleothem isotope values or even growth interruptions, which indicate very dry conditions. Cueva Victoria speleothems provide the first robust terrestrial palaeoclimate archive in this semi-arid region and they respond sensitively to changes in palaeoclimate, predominantly during warm phases. Fast changes in stable isotopes (δ13C, δ18O) with respect to Northern Hemisphere climate changes highlight their potential as a proxy for palaeoclimate reconstruction in the semi-arid south-eastern Spain.
