CHRONOLOGY AND MODELING OF LATE GLACIAL AND HOLOCENE GLACIATIONS IN NEW ZEALAND

Glacial geomorphic and chronologic data from the South Island indicate that New Zealand experienced cold temperatures during the Late Glacial Antarctic Cold Reversal, warming through the Younger Dryas stadial, and long term net warming over the Holocene. We are quantifying paleoclimate from this glacier record by reconstructing glacier geometries, equilibrium line altitudes (ELA) by the accumulation to area ratios (AAR), and numerical modeling experiments. We use a coupled energy-balance and ice-flow model, constrained by the mapped and dated moraines. Both steady state and time dependent simulations are carried out. For Late Glacial time, the temperature estimates derived from the AAR approach and numerical model experiments are consistent. The modeling simulations that achieve optimal fits to the mapped extents of moraines suggest that atmospheric temperature during the ACR was 2-3°C cooler than today, corresponding to a ±20% variance in precipitation relative to present-day. The Late Glacial ELA was generally about 400 m lower than the modern ELA, although there was some spatiotemporal variability in the value. Following the ACR, a net snowline rise of ~100 m occurred through the YD, succeeded by a further long-term net rise of ~100 m between ~ 11,000 and 600 years ago. This pattern of past glacier behavior and climate in New Zealand is different than that observed for the Northern Hemisphere, including northeastern North America.