Paleoclimate Insights from ¹⁰Be Surface-Exposure Dating of Moraine Sequences in the Southern Alps of New Zealand

This thesis presents 10Be surface-exposure chronologies of moraines deposited by mountain glaciers in the Southern Alps of New Zealand during the past 35,000 years. These chronologies are based on a new determination of a local in situ 10Be production rate for the Southern Alps. Seventy-three 10Be dates of terminal moraines place expansions of the Lake Ohau glacier tongue to Last Glacial Maximum (LGM) positions at 32,520 ± 520 yrs ago, 22,510 ± 660 yrs ago, 18,220 ± 500 yrs ago, and 17,690 ± 350 yrs ago, corresponding to snowlines 850 - 750 m below present values. Beryllium-10 dates record a 40% reduction in length of the Lake Ohau glacier tongue by 17,380 ± 510 yrs ago. Twenty-six 10Be dates from late-glacial moraines document resurgence of the Tasman Glacier that culminated at 12,970 ± 300 yrs ago in response to a snowline ~500 m lower than present. Finally, forty-five10Be dates on moraines in the forefield of Cameron Glacier of the Arrowsmith Range, Southern Alps, track fluctuating recession of the glacier terminus since early Holocene time. Palaeo-snowlines were 240 m below present values during the early Holocene, and rose to 110 m below present by late Holocene time. The last resurgence of Cameron Glacier culminated by 523 yrs ago, followed by slow oscillating retreat of the terminus to the present day. Key conclusions are as follows. (1) The timing and magnitude of the LGM at Lake Ohau corresponds closely with glacier signatures in both polar hemispheres and in the tropics, suggesting that LGM cooling was globally synchronous. One possibility is that lower atmospheric CO2 produced global cooling during the LGM. (2) Major recession of the Ohau glacier beginning about 18,000 yrs ago was coeval with the northern Heinrich Stadial-1, implicating a bipolar seesaw mechanism for initiating the southern termination. (3) Tasman Glacier registered the Antarctic Cold Reversal in antiphase with northern stadials, suggesting that a bipolar seesaw mechanism operated in the south over a large geographical footprint. (4) Asynchronous Holocene glacier behavior in the Southern and European Alps reflects either direct summer radiation forcing and/or southward migration of Earth\u27s thermal equator