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Orbital forcing of mid-latitude Southern Hemisphere glaciation since 100 ka inferred from cosmogenic nuclide ages of moraine boulders from the Cascade Plateau, southwest New Zealand

Rupert Sutherland^,1, Kyeong Kim^,2, Albert Zondervan^,3 and Mauri McSaveney^#,3

¹ GNS Science, P.O. Box 30-368, Lower Hutt, New Zealand
² Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721-0092, USA
³ GNS Science, P.O. Box 30-368, Lower Hutt, New Zealand

Cosmogenic nuclide (Be-10) exposure dating of moraine boulders in the Cascade Valley, southwest New Zealand, reveals three phases of glaciation with similar maximum magnitude since 100 ka. In this area, 8–10 lateral moraines were deposited during the Last Glacial Maximum (LGM) at 22–19 ka, and >15 lateral moraines and three end moraines were deposited during recession after the LGM. Also, three exposure ages of 29–33 ka from pre-LGM deposits may indicate increased weathering and erosion at the onset of the LGM in New Zealand, as has been suggested by other studies. An exposure age of 57.8 ± 2.7 ka from one of the highest moraines, combined with previous studies of cave speleothems, glacial features offset by the Alpine fault, the Vostok dust record, and sediment cores, supports the inference that a significant glacial phase culminated at 66–58 ka. A cluster of five exposure ages from older moraines reveals a glacial phase with at least three advance-retreat cycles at 79.0 ± 3.9 ka. Correlation between the ages of glacial periods and the timing of Southern Hemisphere summer insolation minima suggests that orbital forcing has played a first-order role in regulating glacial extent in New Zealand.

Key Words: glacial deposits • moraines • climate • Milankovitch • Last Glacial Maximum • cosmogenic elements • beryllium