CORRELATION OF GLACIAL SEQUENCES TO UNRAVEL PATTERNS OF GLOBAL CLIMATE CHANGE: WHAT RESOLUTION IS NEEDED?

The growth and decay of glacier systems are a sensitive indicator of past and present climate changes. The challenge to sort out the significance of these paleoclimate indicators perhaps lies not in the sensitivity of the glacier system (< 1°C) but rather on assignment of timing to the glacial events. For example, an apparent reported offset of a few hundred years, the length of the present global warming trend, between glacial systems in different polar hemispheres might be taken as either a synchronous event, which could reflect a change in the global energy balance, or out of phase relationship which might be taken as a regional redistribution of heat. Unless any systematic offset in the dating assignment is less than the response time of the glacier system, a robust conclusion about the climate phasing across different spatial areas is unlikely. A part of the challenge may be that dating glacial expansions require somewhat atypical geologic settings and thus can be done in relatively few areas. Glacial retreats provide a wider range of settings for dating, but often times the “date” assigned reflects geologic processes other than the initiation of ablation from climate warming. Suspect conclusions can arise if a maximum age from one area is compared to a minimum age from another area. In cases where both maximum and minimum dates are available on the same glacial event, a typical offset is some ~600 cal years reflecting the duration of glacier cover and any offset from the stratigraphic context.

Although glacier systems can respond on decade time scales to climate, the filtering effect of the geological record (the temporal sum of the resolution of the dating tool, the duration of glacier expansion, and the sedimentary record) currently seems to require that events have durations > 600 cal yr before firm phasing relationships can be ascertained. Efforts must be made to reduce this before the full value of glacial records can contribute to the understanding of climate change.