A new paleoclimate record for North Westland, New Zealand, with implications for the interpretation of speleothem based paleoclimate proxies.

Abstract

New Zealand speleothems can be used as proxy records of terrestrial Southern Hemisphere climate change and can be compared to records from the Northern Hemisphere to evaluate the timing of significant climatic events, and the driving influences of the Antarctic and North Pacific. The interpretation of paleoclimate from stalagmite geochemistry is a complex process. The majority of stalagmite records from New Zealand are based on calcite stable isotope composition, however, recent research into stalagmite trace element composition has shown that multi-proxy records aid paleoclimate interpretations. The complexity of the many processes affecting the geochemistry of calcite forming in a cave system requires assumptions to be made about cave environment conditions. This thesis presents a new high-resolution paleoclimate record based on stable isotope and trace element composition from a West Coast, New Zealand, stalagmite. The assumptions underlying the interpretation of such a record are examined and compared to local environmental field data. In addition, a new method of extracting and analysing calcite fluid inclusions is explored, in order to address some of the issues associated with unknown past stable isotope composition of cave drip water. Field data from the local cave area have demonstrated high natural variability in the stable isotope composition of rainfall, cave drip water, dissolved inorganic carbon, and modern cave calcite. The high modern natural variability raises questions about the validity of assumptions of the stability of the cave environment. The high-resolution record of calcite stable isotope and trace element composition indicates that changes in precipitation amount, the atmospheric temperature of rainfall precipitation, and local environmental water balance are the dominant controls on stalagmite geochemistry on the West Coast. The comparison of this single stalagmite paleoclimate record to other single and multiple stalagmite records from the same region indicate that data from single stalagmites show more variation in past climate, and can be best understood when the modern variability is accounted for with in-depth field measurements of the local environmental processes.