Pleistocene glacial history of the New Zealand subantarctic islands
2018
Abstract. The New Zealand subantarctic islands of Auckland and Campbell,
situated between the subtropical front and the Antarctic Convergence in the
Pacific sector of the Southern Ocean, provide valuable terrestrial records
from a globally important climatic region. Whilst the islands show clear
evidence of past glaciation, the timing and mechanisms behind Pleistocene
environmental and climate changes remain uncertain. Here we present a
multidisciplinary study of the islands – including marine and terrestrial
geomorphological surveys, extensive analyses of sedimentary sequences, a
comprehensive dating programme, and glacier flow line modelling – to
investigate multiple phases of glaciation across the islands. We find
evidence that the Auckland Islands hosted a small ice cap
384 000 ± 26 000 years ago ( 384±26 ka), most likely during
Marine Isotope Stage 10, a period when the subtropical front was reportedly
north of its present-day latitude by several degrees, and consistent with
hemispheric-wide glacial expansion. Flow line modelling constrained by field
evidence suggests a more restricted glacial period prior to the LGM that
formed substantial valley glaciers on the Campbell and Auckland Islands around
72–62 ka. Despite previous interpretations that suggest the maximum glacial
extent occurred in the form of valley glaciation at the Last Glacial Maximum
(LGM; ∼21 ka), our combined approach suggests minimal LGM
glaciation across the New Zealand subantarctic islands and that no glaciers
were present during the Antarctic Cold Reversal (ACR; ∼15 –13 ka).
Instead, modelling implies that despite a regional mean annual air
temperature depression of ∼5 ∘ C during the LGM, a combination
of high seasonality and low precipitation left the islands incapable of
sustaining significant glaciation. We suggest that northwards expansion of
winter sea ice during the LGM and subsequent ACR led to precipitation
starvation across the middle to high latitudes of the Southern Ocean, resulting
in restricted glaciation of the subantarctic islands.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
107
References
9
Citations
NaN
KQI