Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: implications for MIS-2 ice extent and LGM glacial mass balance

Rother, Henrik, Shulmeister, James, Fink, David, Alexander, David and Bell, David (2015) Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: implications for MIS-2 ice extent and LGM glacial mass balance. Earth and Planetary Science Letters, 429 69-81. doi:10.1016/j.epsl.2015.07.033


Author Rother, Henrik
Shulmeister, James
Fink, David
Alexander, David
Bell, David
Title Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: implications for MIS-2 ice extent and LGM glacial mass balance
Journal name Earth and Planetary Science Letters   Check publisher's open access policy
ISSN 0012-821X
1385-013X
Publication date 2015-11-01
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.epsl.2015.07.033
Open Access Status Not Open Access
Volume 429
Start page 69
End page 81
Total pages 13
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 1908 Geophysics
1906 Geochemistry and Petrology
1901 Earth and Planetary Sciences (miscellaneous)
1912 Space and Planetary Science
Abstract During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages.
Keyword New Zealand
Quaternary
Mountain glaciation
10Be surface exposure dating
Last glacial maximum
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Geography, Planning and Environmental Management Publications
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