 |
| Titel |
Reconstruction and paleoclimatic significance of Late Pleistocene niche
glaciation at Mt Aston, Tararua Range, North Island, New Zealand |
| VerfasserIn |
Martin Brook |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142898
|
| Publikation (Nr.) |
 EGU/EGU2017-6576.pdf |
|
|
|
|
|
| Zusammenfassung |
| Evidence for the timing of inter-hemispheric climate fluctuations during the Pleistocene is
important, with reconstructed mountain glacier extents routinely used as a proxy for climate.
While valley glaciers extended out from an ice sheet centred on New Zealand’s Southern
Alps during Pleistocene climate cooling to below present-day sea level, evidence of former
glacial activity on the North Island of New Zealand is rare, in comparison. A newly-identified
glaciated site is Mt Aston, an isolated cirque-like basin within the Tararua Range on New
Zealand’s North Island. Previously published cosmogenic isotope ages and paleo-glacier
reconstructions of a 3 km-long valley glacier 30 km to the north show that paleo-equilibrium
line altitudes (ELAs) increased northwards across New Zealand during the regional last
glacial maximum (LGM). Hence, at this latitude (41˚ 00’ S), only topography >1300 m
above present day sea-level was of feasible elevation to intersect the prevailing
south-westerly airflow and to allow niche glaciers to form. In the basin below Mt
Aston, a c. 0.38 km2 cirque glacier existed with ELA of c. 1290 ± 10 m above
present-day sea level. This paleo-ELA closely approximates the extrapolated ELA trend
surface for the regional LGM. The mean glacier thickness of 35 m gives a maximum
basal shear stress of c. 102 kPa−1, with a mean January temperature at the ELA
of c. 5.5 ˚ C. It is well-established that present-day glaciers in New Zealand are
particularly sensitive to climate change, manifested by glacial advances and retreats in
response to simple mass balance dynamics. Consistent with this, the paleo-glacier
reconstruction implies that rather than simple temperature decreases driving paleo-ELA
depression, changes in south-westerly airflow over New Zealand, bringing moisture-laden
but cool air, maximized snowfall and minimised winter melt. The corollary is that
(1) patterns of Pleistocene glacier fluctuations may be interpreted as responses,
in-part, to precipitation-driven changes, and (2) the extent of LGM glaciation on New
Zealand’s North Island was probably more extensive than previously assumed. |
|
|
|
|
|
|