CALIBRATING HYDROCLIMATE PROXIES IN A SOUTHERN PORTUGUESE SPELEOTHEM

Stable isotopes archived in calcium carbonate cave deposits such as stalagmites have been widely used to reconstruct past climates. However, various processes can influence the isotope signal recorded in speleothems, potentially obscuring climate signals. Stalagmite oxygen isotopes can record the d¹⁸O values of regional precipitation and hence hydroclimate, but processes such as soil and karst water evaporation, mixing, and seasonally biased carbonate precipitation may complicate the target signal. Stalagmite carbon isotopes can record soil metabolism, which is also related to hydroclimate, but are also impacted by kinetic effects during degassing and calcite precipitation. Here we compare high-resolution oxygen and carbon isotopes in a small stalagmite (5 cm in height) with a modern top from Companheira cave in in southern Portugal. The sample was sectioned and milled at a 10-20 mm resolution along a 1 cm wide track in the central growth axis using a Mercenteck Micromill. Samples were analyzed on a Thermo Gas Bench II coupled to a Thermo Delta Advantage isotope ratio mass spectrometer. Speleothem isotope data will be compared with regional precipitation and air temperature from the Algarve region. These data will allow us to test if speleothem calcite accurately reflects precipitation amounts. Such comparison will provide more confidence in a reconstruction of hydroclimate in southern Portugal. These time series will allow for a more comprehensive evaluation of dynamical changes in the regional climate system through time, particularly in the spatial extent and intensity of the Azores High, a system which strongly impacts precipitation in this region.