Over the last 30 years, speleothems have been increasingly investigated for their potential use as palaeoenvironmental and palaeoclimatic indicators. Particular attention has focussed on the oxygen isotopic variations in speleothem calcite as a proxy for temperature, based on the temperature dependent fractionation of stable oxygen isotopes between water and precipitated calcite. The method requires the isotopic composition of past waters to be either known or accurately estimated. As speleothems are deposited from percolating rainwaters, an adequate expression is required to describe changes in the long-term averaged isotopic composition of precipitation with time.

Quantitative and semi-quantitative approaches to the derivation of palaeotemperatures from speleothems have to date met with limited success, owing to the difficulty in quantifying the parameters that control oxygen isotope variability in speleothem calcite. This has led to the extensive interpretation of speleothems as representing qualitative palaeotemperature signals, where the direction and magnitude of change in the isotopic composition of speleothem calcite is interpreted as long term surface temperature variations at the site.

Here we use the modern isotopic data from six Australian and New Zealand IAEA/WMO stations to characterise variations in the isotopic composition of regional rainfall. The dominant climatic factors controlling the modern isotopic variability in the region are constrained. An expression for the spatial and temporal variations in the isotopic composition of precipitation, and a speleothem temperature equation for the region are presented. The equation was evaluated at sites of known modern calcite composition before being applied to two published New Zealand speleothem 18O records, the only ones from the region which span the LGM.

The results suggest LGM temperatures Å6°C cooler than present in New Zealand, with cold conditions between 30 and 21 ka with several minor warming events. This is followed by a progressive warming from 18 to ca. 13 ka, reaching a temperature maximum of ~1°C at ~9 ka. The late Holocene appears to be characterised by temperatures slightly cooler than present. Good agreement is obtained with other independent records from the Southern Hemisphere, in particular the Antarctica ice core records.