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

摘要

New Zealand speleothems can be used as proxy records of terrestrial Southern Hemisphereclimate change and can be compared to records from the Northern Hemisphere to evaluate thetiming of significant climatic events, and the driving influences of the Antarctic and NorthPacific. The interpretation of paleoclimate from stalagmite geochemistry is a complexprocess. The majority of stalagmite records from New Zealand are based on calcite stableisotope composition, however, recent research into stalagmite trace element composition hasshown that multi-proxy records aid paleoclimate interpretations. The complexity of the manyprocesses affecting the geochemistry of calcite forming in a cave system requires assumptionsto be made about cave environment conditions.This thesis presents a new high-resolution paleoclimate record based on stable isotope andtrace element composition from a West Coast, New Zealand, stalagmite. The assumptionsunderlying the interpretation of such a record are examined and compared to localenvironmental field data. In addition, a new method of extracting and analysing calcite fluidinclusions is explored, in order to address some of the issues associated with unknown paststable isotope composition of cave drip water. Field data from the local cave area havedemonstrated high natural variability in the stable isotope composition of rainfall, cave dripwater, dissolved inorganic carbon, and modern cave calcite. The high modern naturalvariability raises questions about the validity of assumptions of the stability of the caveenvironment. The high-resolution record of calcite stable isotope and trace elementcomposition indicates that changes in precipitation amount, the atmospheric temperature ofrainfall precipitation, and local environmental water balance are the dominant controls onstalagmite geochemistry on the West Coast. The comparison of this single stalagmitepaleoclimate record to other single and multiple stalagmite records from the same regionindicate that data from single stalagmites show more variation in past climate, and can be bestunderstood when the modern variability is accounted for with in-depth field measurements ofthe local environmental processes.