Holocene glacier chronologies: Are ‘high-resolution’ global and inter-hemispheric comparisons possible?

Abstract

In the context of reconstruction of Holocene glacier chronologies, there has been a clear tendency during the past few decades towards imprecise use of the term ‘high resolution’. Furthermore, it seems to be increasingly assumed that recently developed terrestrial cosmogenic nuclide dating (TCND) is replacing earlier dating methods. Although recent glaciological knowledge clearly reveals the futility of oversimplified global and inter-hemispheric correlation on the basis of few ‘key’ sites, such comparisons are widely attempted. Stimulated by the example of a recently published article relating to the Southern Alps of New Zealand (Schaefer et al., 2009, Science 324: 622—625) we highlight some related potential problems with the interpretation of Holocene glacier chronologies. In particular, we consider (1) that the term ‘high resolution’ should be applied only to decadal-scale resolution or better and, therefore, not to TCND-based chronologies; (2) that discontinuous moraine chronologies should not be termed high resolution and that their potential geomorphological limitations should be acknowledged; and (3) that TCND-based moraine chronologies should not automatically replace evidence available from other dating techniques but that they should be regarded as complementary and an opportunity for mutual evaluation. Owing to local and regional patterns in glacier response to climate, it is concluded (4) that intra-hemispheric synchroneity in high-resolution Holocene glacier variations is still unproven, and hence (5) that inter-hemispheric comparison is arguably premature, if not impossible. Finally, it is suggested (6) that the first priority for research in this field should be to establish the spatial patterns in glacier behaviour evident at various scales in Holocene records.