Multi-proxy constraints on the climatic significance of trace element records from a New Zealand speleothem

Trace element concentrations and uranium isotope ratios are reported for a speleothem from the South Island of New Zealand. TIMS uranium-series dating of the speleothem indicates it to have grown from 31 000 years ago to the present, providing a continuous record of the last deglaciation. Trace elem ent abundances measured in this speleothem using ICP-MS are found to exhibi t strong temporal relationships with delta(13)C and other measured variable s, and with the environmental changes inferred from them. Strontium and bar ium concentrations are positively correlated with inferred changes in the p roductivity and extent of vegetation cover above the cave. Magnesium concen tration appears to have responded to changes in groundwater residence time, assumed to have an inverse relationship with effective meteoric precipitat ion above the cave. The degree of U-234/U-238 disequilibrium also appears t o have varied in response to hydrological changes, and together with the ma gnesium data implies a post-glacial increase in regional effective precipit ation to have culminated ca. 13 000 cal yr B.P., some 2000 years after a dr amatic post-glacial increase in forest extent previously inferred for the r egion. This increase in forest extent is thus unlikely to have been caused by a significant increase in precipitation, and is assumed to have been dri ven predominantly by a rapid increase in regional temperature, centred on 1 5 000 calendar years before present. (C) 2000 Elsevier Science B.V. All rig hts reserved.