Dating stalagmites in mediterranean climates using annual trace element cycles

Gurinder Nagra,John Hellstrom,Pauline C Treble,Andy Baker,Martin S Andersen,Petra Bajo

doi:10.1038/s41598-017-00474-4

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.

Highlights

Stalagmites are invaluable geochemical archives of past climate[1,2,3]
The principal components analysis (PCA)/peak counting method for building chronologies will be most effective if only those elements that have the clearest cycles are included, it can be seen from Fig. 2 that the choice of elements may vary between stalagmites
Similar agreement was found between results for stalagmites LAB-S1 and YD-S2

Summary

Introduction

Stalagmites are invaluable geochemical archives of past climate[1,2,3]. the sensitivity of stalagmite geochemistry to local biomass, soil and karst processes[4,5,6,7] suggests the need to validate the stalagmite record, using cave monitoring and modern stalagmites. Modern stalagmites allow us to compare the stalagmite geochemical record to instrumental climate and local environmental data[9,10,11]. This deepens our knowledge of how dripwater geochemical signals are incorporated into the speleothem calcite. Annual lamina counting is an established method in tree-rings, ice-cores, corals, lake sediments and speleothems to reconstruct annually resolved records[1] It may result in a more precise chronology if annual growth increments are resolvable and provided that there are no interruptions to growth in the record. If multiple trace elements are used and a process-based understanding of the variations within stalagmites are applied, we may derive a more confident chronology

Methods

Results

Discussion

Conclusion