Dating stalagmites in mediterranean climates using annual trace element cycles

Abstract

Speleothems may preserve geochemical information at annual resolution, preserving information about past hydrology, environment and climate. In this study, we advance information-extraction from speleothems in two ways. First, the limitations in dating modern stalagmites are overcome by refining a dating method that uses annual trace element cycles. It is shown that high-frequency variations in elements affected by prior calcite precipitation (PCP) can be used to date speleothems and yield an age within 2-4% chronological uncertainty of the actual age of the stalagmite. This is of particular relevance to mediterranean regions that display strong seasonal controls on PCP, due to seasonal variability in water availability and cave-air pCO2. Second, using the chronology for one stalagmite sample, trace elements and growth-rate are compared with a record of climate and local environmental change i.e. land-use and fire, over the 20th century. Well-defined peaks in soil-derived trace elements and simultaneous decreases in growth-rate coincide with extreme annual rainfall totals in 1934 and 1974. One of which, 1934, was due to a recorded cyclone. We also find that bedrock-derived elements that are dominated by PCP processes, reflect a well-known period of drying in southwest Australia which began in the 1970's.