The influence of sub-glacial bed evolution on ice extent: A model-based evaluation of the Last Glacial Maximum Pukaki glacier, New Zealand

摘要

A potential complication in using glacier extent to estimate paleoclimatic conditions is the influence of glacier bed evolution on changes in ice extent over time. Here, we examine this issue through model-based reconstructions of the Last Glacial Maximum (LGM) Pukaki glacier, Southern Alps, New Zealand, whose LGM extents are exceptionally well defined by lateral and terminal moraines. Using the well-dated moraine limits as an empirical constraint on maximum ice extents, we employ a one-dimensional glacier flowline model driven by a mass balance model in order to evaluate the influence of climate and glacier bed profile on the extent of the LGM Pukaki glacier. The LGM glacier bed is buried by Lateglacial and post-glacial sediment, so we calculate bed profiles using a modified version of the one-dimensional model and available geologic constraints. A best fit to the moraine record occurs with a LGM temperature of 7-8 °C cooler than present, with precipitation ranging from 80% to 100% of present levels. Modeling of the bed profile evolution indicates that bed changes alone could account for kilometer-scale changes in glacier width and length.