Abstract
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.
Highlights
The Southern Ocean plays a critical role in the climate system, connecting the three main ocean basins (i.e. Atlantic, Pacific, and Indian) and modulating regional to global atmospheric temperatures and weather patterns on historic to millennial timeframes (Anderson et al, 2009; Marshall and Speer, 2012; Steig et al, 2009; WAIS Divide Project Members, 2015; Turney et al, 2016a; Jones et al, 2016)
Hydrographic charts hint at the presence of drowned moraine features within the over-deepened valleys of the eastern coasts of both islands, including Norman Inlet on Auckland Island (Fig. S9) and Perseverance Harbour on Campbell Island, which have a number of promontories shown in the topographic maps that may signify the presence of preserved moraines
We find evidence for multiple distinct phases of glaciation on both Auckland and Campbell Islands and propose the following sequence of events: (1) the Enderby Glaciation at ∼ 380 ka consisting of extensive glaciation covering large portions of the islands, most likely occurring during MIS 10; (2) a more restricted glacial period prior to the Last Glacial Maximum (LGM) that formed substantial valley glaciers on Campbell and Auckland Islands at around 72–62 ka; and (3) a limited eLGM–LGM glacial advance, comprising either valley glaciation with glaciers no longer than a few kilometres prior to retreat to highaltitude cirques or severely restricted glaciation limited to these cirques
Summary
The Southern Ocean plays a critical role in the climate system, connecting the three main ocean basins (i.e. Atlantic, Pacific, and Indian) and modulating regional to global atmospheric temperatures and weather patterns on historic to millennial timeframes (Anderson et al, 2009; Marshall and Speer, 2012; Steig et al, 2009; WAIS Divide Project Members, 2015; Turney et al, 2016a; Jones et al, 2016). During the Late Pleistocene (110 000 to 11 650 years ago, 110–11.65 ka), marine and terrestrial records across the midlatitudes demonstrate broadly similar trends to those reported from Antarctic ice core sequences (EPICA Community Members, 2006; Kaplan et al, 2008; McGlone et al, 2010; Moreno et al, 2009; Pahnke et al, 2003; Pedro et al, 2015). To gain a fuller understanding of climate dynamics over the region it is vital we exploit these currently underutilised archives fully
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
