Comparison of high resolution sub-annual records of trace elements in a modern (1911-1992) speleothem with instrumental climate data from southwest Australia
Date
2003
Authors
Treble, Pauline
Shelley, Michael
Chappell, John
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Elsevier
Abstract
High spatial resolution measurements of Mg, P, U, Sr, Ba and Na using 193-nm excimer laser-ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern Australia. The age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew (1911-1992). This chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content. Eleven laser-ablation transects across a ∼0.5 mm wide section of the speleothem growth axis were measured. Cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record. P and U positively, and Mg inversely, mimic the sudden 20% decrease in annual rainfall experienced by this region since 1965. We argue that P from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil, owing to the low P retention capacity of southwest Australian soils. Both vegetation activity and the transport of vegetation-derived HPO42- are sensitive to rainfall. Groundwater P concentration may also influence the transport of U through the strong affinity between phosphate and uranyl ions. Mg appears to be sensitive to groundwater residence time as this affects drip-water Mg/Ca composition by preferential loss of Ca during drier episodes when calcite precipitates before reaching the stalagmite. The effects of groundwater residence time may also be important for Sr on inter-annual scales. However, the behaviour of Sr on the annual cycle is opposite to Mg but compatible with Ba and Na, which are shown to depend on speleothem growth rate.
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Keywords: climate cycle; laser method; magnesium; phosphorus; proxy climate record; speleothem; trace element; uranium; water chemistry; Australia Annual cycle; Inductively coupled plasma; Laser ablation; Magnesium; Phosphorus; Rainfall; Speleothem; Trace element; Uranium
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Earth and Planetary Science Letters
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Journal article
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2037-12-31
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