Records of Rapid Late Quaternary Environmntal Change From Auckland Maar Lakes, New Zealand

High-resolution Late Quaternary paleoclimate archives are preserved in the sedimentary records contained in Auckland maar crater lakes. In particular, Orakei, Onepoto, Pukaki, Hopua and Pupuke maar lakes contain high-resolution sediment records with excellent chronological control for the period from ca 50 ka BP to today. A wide range of proxies have been measured from the maar crater sediments including: pollen and diatom paleoecology, environmental magnetism, grain size, major oxide and trace element geochemistry, total organic carbon, nitrogen and sulphur, plus bulk organic matter stable isotopes. Pollen analysis has been carried out on Onepoto and Pukaki cores that span the last ca 70 and 100 ka respectively in which marked vegetation changes reflect orbital forcing. In particular, reduction of forest and expansion of grass and shrublands coeval with deposition of the Okaia tephra (ca 29 kyr BP) is interpreted as the start of the LGM, after which cool, dry and windy conditions dominated, although our multi-proxy approach indicates that the situation is more complex with warmer/wetter phases punctuating the LGM. Warming commenced ca 17.7 ka BP and is apparent in multiple proxies from the maar lake records. However, the pollen record does not reflect the marked changes displayed in many of the other proxies during the late glacial. Similarly, the Holocene pollen record from Lakes Pupuke and Hopua indicates environmental stability and shows little change throughout the pre-human Holocene though a sustained ca 360 yr long phase of apparently drier conditions between ca 7.9 and 8.2 ka BP is apparent in other proxies. The multi-proxy approach allows us to reliably infer environmental changes in the lakes and catchments. Furthermore, compound-specific carbon and hydrogen isotope analysis of lipid biomarkers extracted from the sediment organic matter and oxygen isotope analysis of diatom silica, sponge spicules and organic matter cellulose are being undertaken to allow us to better understand the paleotemperature and paleohydrological controls on the complex isotopic signal contained in the maar lake sediments.