A 2500-YEAR RECORD OF HYDROCLIMATE VARIABILITY AS EVIDENCED BY LASER ABLATION ANALYSIS OF TRACE ELEMENTS AND STABLE ISOTOPES IN PORTUGUESE SPELEOTHEMS

Speleothems are important records of paleoclimate in karst regions as they contain trace element and stable isotope information which depend on hydroclimate variability. Speleothems of the Iberian Peninsula are of particular interest due to the relationship of Iberian hydroclimate with the behavior of the Azores High and the North Atlantic Oscillation (NAO). We investigated three well-dated speleothems from Buraca Gloriosa (BG) cave in western Portugal, ideally located within the region of influence of the Azores High, making these stalagmites suitable for use as hydroclimate proxies. Prior calcite precipitation (PCP) is presented as a dominant mechanism of stable carbon isotope and trace element variability and is attributed to higher Mg/Ca, Sr/Ca, and Ba/Ca ratios as well as increased carbon isotope (δ¹³C ) values. During drier periods, water residence time in karst bedrock is increased, increasing PCP and concentrating heavy earth metal in speleothem drip water. Spectral density analysis of trace element time series reveals longer period (multidecadal), presumably climate-driven, oscillations. Comparing Mg/Ca and P/Ca we observe an inverse relationship highlighting the dry and wet cycles in Iberian hydroclimate. In addition to these seasonal cycles, longer-term trends of arid and humid intervals over the last 2500 years are evident in the trace element records. Together, these high-resolution trace element records will complement existing carbon and oxygen isotope records from the three stalagmites and create a robust multi-proxy reconstruction of past Iberian hydroclimate.