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

Andrew M. Lorrey,John-Mark Woolley,James A. Renwick,Matthew S. Lachniet,Shaun Eaves,Helen Bostock,Adam Hartland,Nicolas C. Fauchereau,Paul W. Williams,Vidya Varma

doi:10.3390/quat3030024

Abstract

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 δ18O 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 δ18O 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 δ18O 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 δ18O 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 δ18O data indicate that caution is needed prior to merging δ18O 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.

Highlights

Using the Waitomo δ18O records recently gathered for Synthesis and AnaLysis (SISAL), we demonstrate the utility of COnstructing Proxy Records from Age Models (COPRA) Monte Carlo age model simulations to explore some isotope master record generation techniques
For New Zealand speleothem isotopic data series that were reviewed and age modelled for SISAL, only 10 records extended beyond the late glacial, and half of those limited records extended prior to the last glacial maximum (LGM) (Table 1 and Figure 4)
Holocene speleothem coverage includes series from both main islands Each of these regions has a minimum of three speleothems that cover all or part of the Holocene, with sample resolution widely varying from sub-decadal to multi-centennial scales (Figure 4)

Summary

Introduction

New Zealand provides critical Southern Hemisphere palaeoclimate data and perspectives about. Late Quaternary environmental change [1,2]. Atmospheric circulation regimes that influence this region produce strong, heterogeneous regional hydroclimate impacts from key modes of variability like the El Niño-Southern Oscillation, Madden-Julian Oscillation, the Interdecadal Pacific Oscillation, and the Southern Annular Mode [3,4,5,6,7]. New Zealand speleothems can help contextualize global change patterns and clarify teleconnections that operate across a range of spatiotemporal scales [8]. We provide an overview of New Zealand speleothem data that our team has provided to the Past Global Changes (PAGES) Speleothem Isotopes Synthesis and AnaLysis (SISAL) initiative [9]. New Zealand speleothem data (see Table 1) comprise a significant proportion of the Southern

Methods

Results

Conclusion