Re-visiting New Zealand's Holocene glacier chronology - Time to overcome certain paradigms and consider spatial differentiation?

The Southern Alps of New Zealand are regarded as an important key site for studying Holocene glacier chronologies in the mid-latitudinal southern hemisphere. Consequently, most global reviews of the topic include respective records and utilise them for (intra-)hemispheric correlations and palaeoclimatic analyses. These particular approaches are, however, closely connected to three common paradigms: (i) There is a representative and reliable compilation of glacier records for the entire Southern Alps, (ii) the European Alps are a well-suited and appropriate northern hemispheric glacier region for any comparative purpose, and (iii) air temperatures are the sole relevant driver of glacier variability in New Zealand.

In a recent study ¹⁰Be cosmogenic radionuclide dating (CRN) and Schmidt-hammer exposure-age dating (SHD) were applied to extent the regional database and obtain surface-exposure ages from moraines on Holocene glacier forelands in eastern Aoraki/Mt.Cook National Park, Arrowsmith Range, and Liebig Range. Re-calculated published ¹⁰Be CRN age data were, alongside previously obtained results from both central Aoraki/Mt.Cook and Westland/Tai Poutini National Parks, utilised for a comparative chronological analysis. Unlike previous approaches glacier records were differentiated by sub-regions of the Southern Alps and interpreted accordingly. Neither amalgamation of individual glacier records nor non-differentiated compilation took place. This multi-proxy approach was combined with detailed geomorphological mapping and assessment to tackle the regionally specific 'geomorphological uncertainty' potentially interfering with all subsequent interpretation of chronological data.

Chronological analysis and subsequent palaeoclimatic interpretation worked well if they were restricted to sub-regional levels. In the Arrowsmith Range strong glacial activity and multiple advances during the Early Holocene could be confirmed, with a similar pattern likely for the Liebig Range. A correspondence to frequent Early Holocene cold periods indicated by rock glacier activity in the Ben Ohau Range is obvious. But in contrast to these drier eastern sub-regions no evidence for Early Holocene advances exists for central and western sub-regions. At Classen Glacier in eastern Aoraki/Mt.Cook National Park, geomorphologically reliable morainic evidence shows a significant Mid-Holocene advance at c. 5.4 ka. It is possibly corresponding to evidence from Mueller and Tasman Glaciers. This advance coincides with an intensification of westerly airflow established around that time. Together with a 'Little Ice Age'-maximum during the mid-/late 18th century CE in Aoraki/Mt.Cook National Park and recent advances at the end of the 20th century it also indicates that (seasonal) atmospheric circulation patterns, in particular the intensity of westerly airflow, and precipitation should not be ignored as climatic factors influencing glacier variability. Finally, with its pronounced West-East precipitation gradient potentially responsible for different sub-regional glacier records, the Southern Alps share several glaciologically relevant climatic conditions with the maritime Scandinavian Mountains, but hardly with the generally drier European Alps.

Further refinement of the Holocene glacier history for the Southern Alps constitutes a significant challenge. It requires a more detailed understanding of both the variability of individual glacier records and the need for spatial differentiation before attempting to compile a representative Holocene glacier chronology for the entire Southern Alps. Furthermore, certain common paradigms need to be critically reviewed and re-considered.