Late Quaternary Climate Variability and Change from Aotearoa New Zealand Speleothems: Progress in Age Modelling, Oxygen Isotope Master Record Construction and Proxy-Model Comparisons

摘要

We re-evaluated speleothem isotope series from Aotearoa New Zealand that were recently contributed to the Speleothem Isotopes Synthesis and AnaLysis (SISAL) database. COnstructing Proxy Records from Age Models (COPRA) software was used to produce Bayesian age models for those speleothems. The new age modelling helped us examine Late Quaternary temporal coverage for the national speleothem network, and also supported our exploration of three different isotope master record generation techniques using Holocene 18O data from Waitomo. We then applied the output from one of the isotope master record techniques to test an application case of how climate transfer functions can be developed using climate model simulated temperatures. Our results suggest Holocene 18O trends at Waitomo capture air temperature variations weighted toward the primary season of soil moisture (and epikarst) recharge during winter. This interpretation is consistent with the latest monitoring data from the Waitomo region. Holocene 18O millennial-scale trends and centennial-scale variability at Waitomo likely reflect atmospheric circulation patterns that concomitantly vary with surface water temperature and the isotopic composition of the Tasman Sea. A climate model simulation context for the Holocene millennial-scale trends in the Waitomo 18O isotope master record suggest that site is sensitive to changes in the subtropical front (STF) and the Tasman Front. Our comparison of isotope master record techniques using Waitomo 18O data indicate that caution is needed prior to merging 18O data series from different caves in order to avoid time series artefacts. Future work should incorporate more high-resolution cave monitoring and climate calibration studies, and develop new speleothem data from northern and eastern regions of the country.