CLIMATIC SIGNIFICANCE OF HOLOCENE GLACIER FLUCTUATIONS IN NEW ZEALAND

Holocene glacier fluctuations in New Zealand are represented by well-preserved moraine complexes in the Southern Alps. Recent cosmogenic dating of Holocene moraine sequences has allowed for interhemispheric comparisons of glacier advances and hence climate change. However, Balco (2009, Science, v 324, p 599-600) and others have asked “Can the timing and magnitude of observed past glacier changes in a particular region be explained by stochastic variability inherent in a steady climate, or is a change in the mean climate required?” To understand better the link between glaciers and climate during the Holocene, we evaluate possible past climate parameters by simulating ice extent at several well-preserved moraines deposited by the Cameron Glacier in the Arrowsmith Range, Southern Alps, New Zealand. We use a coupled 2-D ice-flow and distributed energy balance model with a snow transport component, the latter of which is necessary because, in its present-day configuration, this glacier receives a component of its accumulation from frequent snow avalanches. In our first experiment, we use steady-state simulations to identify the temperature and precipitation forcing required to fit the modelled Cameron Glacier to each of the geomorphically-defined moraine ridges. In our second experiment, we forced the glacier model with a time series of stochastic climate forcing that excludes a background temperature change. We discuss results of these tests, which permit assessment of the sensitivity and response of the Cameron Glacier to different modes of climate variability.