RESPONSE OF NEW ZEALAND GLACIERS TO THE CLIMATE EVENTS OF THE LITTLE ICE AGE: A TEMPLATE FOR OLDER CLIMATE CHANGES?

Glacial responses of the relatively small climate event known as the Little Ice Age suggest that glacier systems provide sensitive, reliable indicators of older climate events. The Muller, Hooker, Tasman, Murchison, Claussen and Godley glaciers are among the largest in New Zealand and drain eastward off the Southern Alps. Historical accounts and a newly developed lichen calibration curve, show that as a group these glaciers are undergoing a massive retreat begun in the 1890’s but were in extended positions in the 1860’s and 1720’s and earlier. Some of these systems record all of these expansion-contraction cycles; others retain evidence of only the last cycle. Moreover, the relative amount of surface lowering vs. marginal retreat depends on local conditions (e.g. debris cover), but all began to retreat at the same time within the resolution of the dating techniques.

At temporal scales longer than a few decades these patterns are consistent with the behavior of glacial systems across the Northern Hemisphere and with paleo-climate reconstruction of the latter part of the Little Ice Age. When carefully considered then, glacial systems should provide key insights about climate changes in the more distant past. Some considerations are 1) the dominate signal from glacial landforms/ sediments is deglaciation responding to increased ablation, cooling signals are contained within the timing of advances events. 2) multiple systems must be compiled to counter the likelihood that any specific sequence my not contain all expansions, and 3) the climate signals should be of the magnitude of the Little Ice Age or larger to overcome the influence of local meteorological/ glaciolgical conditions.