A Record of Environmental and Climatic Change from the West Coast, South Island, New Zealand, using Beetle Fossils

Abstract

Fossil beetle based palaeoclimatic and palaeoenvironmental reconstructions are presented from the Westport region, West Coast, South Island, New Zealand for the last glacial cycle. They include the longest continuous fossil beetle record from New Zealand, covering 16,000 years over the OIS 3/OIS 2 transition. Early last glacial (OIS 4) and mid- Holocene (OIS 1) reconstructions are also presented. The assumptions underlying fossil beetle research in New Zealand are tested indicating beetles are suitable proxies for reconstructing palaeotemperature and palaeoprecipitation. This thesis provides the first quantitative estimates of temperature and precipitation from the Westport region for the last glacial. Reconstructed temperatures indicate stadial cooling was seasonal. Maximum cooling was ca. 5℃ in winter and ca. 2-3℃ in summer. Winter cooling is consistent with previous quantitative estimates from New Zealand. Mean annual precipitation decreased a maximum 35-40% during stadials. Temperatures and precipitation varied during OIS 3/2 indicating multiple possible drivers for glaciation. A glacial advance ca. 34-28ka BP correlates with ca. 5℃ winter cooling and ca. 40% less precipitation, which supports temperature driven glaciation whereas a glacial advance ca. 24-22ka BP correlates with ca. 3℃ winter cooling and precipitation similar to present, which supports precipitation forced glaciation. Palaeoenvironmental reconstructions of stadial vegetation from the Westport region indicate lowland Nothofagus fusca-type forest during OIS 4 and a forest-grassland mosaic during OIS 3/2. These records contrast with pollen-based reconstructions of a treeless landscape in Westport during stadials but are consistent with quantitative estimates of stadial cooling. A shift of reproductive strategy in arboreal vegetation may explain the lack of tree pollen in stadial pollen records. This is significant for our understanding of glacial palaeoecology and palaeoclimatology as pollen records may not accurately represent stadial vegetation.