The Last Glacial transition and Holocene ecological change in Arthur’s Pass National Park, New Zealand

This study improves our understanding of paleo-climate and -environmental change in the high-country South Island New Zealand focusing on formerly glaciated valleys near Arthur’s Pass. The area is of importance being positioned under a steep precipitation gradient on the lee side of the Southern Alps. Be-10 exposure ages (n=37) of ice limits, mapped as terminal moraines deposited during the last deglaciation through to late Holocene, span the past 17 000 years. The glacial record from well-preserved moraine sequences within the valley floor and glacial benches (850 to 1350m) demonstrates an initial post-LGM fast retreat that confirms previous studies (e.g. Shulmeister et al., 2010). Coupled with available in-valley exposure ages from Misery, Dobson and McGrath Moraines (Fink et al, 2017), a comprehensive regional deglacial pattern emerges. The Be-10 ages at Misery Moraines, subject of an early debate supporting a Younger Dryas glacial advance in the Southern Hemisphere (Ivy-Ochs et al. (1999), are re-dated to the Antarctic Cold Reversal (~14-15 ka). The record in headwater valleys of the Bealey and Otira rivers is largely obscured by slope-processes making conclusive observations relating to glaciation difficult. Consequently, early to middle Holocene moraines ages were not recovered in these valleys in contrast to nearby Dart Valley (Dowling et al., 2021). There is strong evidence at Otira headwall for a Little Ice Age glacial moraine limit. Several non-glacial boulders yield ages of 6.7ka, 4.2ka, 2.2ka and 1.7ka in the over steepened upper reaches of Bealey and Otira valleys that may reflect landslides associated with separate seismic events. In addition to our glacial chronology, we report on a well constrained record from Lances Tarn (Pb-210, and 37 radiocarbon dates over 4 m core length), a moraine-impounded bog at the saddle of Arthur’s Pass. This record spans ~13 000 years and displays post-glacial environmental change. The pollen record indicates typical succession from herb field through to closed forest, similar to other regional records (e.g. McGlone et al., 2004). The onset of Holocene like conditions is observed early c12ka, unlike central and lower South Island (~10ka). The area is influenced by persistent westerly flows through the entire record but with a reduction in flow in Early Holocene between 9.5 and 8.5ka, causing drier conditions in agreement with other records in Tasmania (Mariani and Fletcher, 2017 also in Patagonia (Moreno et al., 2020). There is little evidence of burning until c2.2ka when grass pollen rises sharply and charcoal counts increase, indicating a change in evapotranspiration (drying). Increased fires are evident from the onset of human arrival 750 years ago. The largest change in fire history and sediment transport occurs after European settlement ~ 1850’s, when intensive deforestation is evident in the pollen record. © The Authors

Keywords

Glaciers, Quaternary period, Ecology, New Zealand, Glaciers, Alps, Southern Hemisphere, Little Ice Age

Citation

Adams, P. M., Fink, D., Shulmeister, J., Woodward, C., Fujioka, T., Simon, K. (2021). The Last Glacial transition and Holocene ecological change in Arthur’s Pass National Park, New Zealand. Paper presented to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 54). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf

URI

https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf
https://apo.ansto.gov.au/dspace/handle/10238/14412

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