Regional climate variability and ecosystem responses to the last deglaciation in the northern hemisphere from stable isotope data and calcite fabrics in two northern Adriatic stalagmites

Geochemical and physical changes along the growth axis of speleothems are controlled by climate as well as the dynamics of the host karst system. Discriminating between the two is one of the major challenges in assembling robust cave palaeoclimate records. Overcoming this dilemma may be achieved by investigating multiple properties from two or more speleothems from the same cave, spanning the same time interval. In this study, we use high-resolution stable oxygen and carbon isotope (delta C-13 and delta O-18), morphological and petrographic data from two calcite stalagmites (SV1 and SV7) from Grotta Savi, Italy, to help constraining the regional climate conditions during the Younger Dryas. The new SV1 record, spanning 15.3-9.4 ka, builds on a previously published low-resolution stable isotope time series. It is anchored by 22 new U-Th ages and lamina-counting, yielding a refined age model that supersedes the previous one. The SV7 record is anchored by 8 U-Th ages and spans 13.1-10.5 ka, partially overlapping the SV1 record. Together, the morphological and geochemical characteristics of SV1 and SV7 allow us to identify site-specific processes driving the isotopic variations. This enables us to explore the degree of complacency in speleothems whereby, periodically, a speleothem is insensitive to recording a climate signal, due to aquifer hydrology and network evolution. The model suggests that delta O-18 is a proxy for the infiltration amount that reaches the site of deposition, which, in the case of SV7, was buffered by the aquifer hydrology. The interpretation of delta C-13 in both stalagmites is more complex, being influenced by both temperature and hydrology. Only a comparison of the two stalagmite records allows us to recognise a decoupling between the effects of hydrology and temperature. According to our interpretation, the most distinctive climate information of the Younger Dryas was the high hydrological variability, with phases dominated by seasonal infiltration within an overall cooling trend. Our record also reveals a significant Early Holocene climate anomaly - centred at 10.4 ka - whose magnitude was possibly amplified by local synoptic conditions. Our research demonstrates the importance of investigating several complementary proxies, particularly from morphologically diverse stalagmites. When monitoring data are not available, fabric and lamina thickness can be fundamental to unravelling the dominant control of hydrology or temperature on stable isotopes. (C) 2013 Elsevier Ltd. All rights reserved.