Vegetation and climate of Auckland, New Zealand, since ca. 32 000 cal. yr ago: support for an extended LGM

Abstract

Auckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid‐latitudes. A new pollen record from Kohuora maar crater, Auckland, displays vegetation and climatic changes for the past ca. 32 000 years. Of particular interest are the inferred climatic patterns for the first part of the interval, encompassing the Last Glacial Maximum (LGM). The Kohuora record corresponds closely with pollen records from other Auckland sites indicating that the patterns observed are at least regional in extent. It is also broadly consistent with a variety of palaeoenvironmental evidence from across New Zealand, including the glacial record from Westland, other palynological records from North Island, other palaeoecological records from the South Island, and aeolian quartz sequences from western North Island. These records show that glacial conditions prevailed across most, if not all, of New Zealand during the interval ca. 29–19 k cal. yr BP, longer and earlier than the LGM sensu stricto. We suggest that the term extended LGM (eLGM) may be more appropriate for the New Zealand region. Within this predominantly cold interval, the Auckland pollen records indicate a climatic amelioration for the interval ca. 26–24 k cal. yr BP, also consistent with other palaeocological data from Canterbury, that fall within a period of climate amelioration recognised between the first two eLGM glacial advances in Westland. We refer to this warming interval as the eLGM Interstadial. The ca. 27 k cal. yr BP Kawakawa/Oruanui tephra is instrumental in most of these inter‐site comparisons and occurs after the first peak of eLGM cooling in a short‐lived comparatively mild phase. A subsequent return to apparently colder climate in the Auckland records may indicate a volcanic cooling effect or, more likely, widespread landscape disturbance following this major eruption event. Strong correspondence between biotic responses, glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the eLGM and eLGM Interstadial may be more widely registered, at least across the Southern Ocean. Support for this assertion comes from parallel investigations in western and southernmost South America and isotopic and palaeoecological records from Southern Ocean marine cores. Recent reconstructions of the globally averaged ice‐equivalent sea‐level history are in line with this evidence from the Southern Hemisphere, suggesting that the eLGM may have a global registration. In light of these observations, we suggest a re‐examination of the defined timing of the LGM along with renewed effort to establish climatic patterns during this period and understand their causes. Copyright © 2007 John Wiley & Sons, Ltd.

Cooling and changing seasonality in the Southern Alps, New Zealand during the Antarctic Cold Reversal

“…This is consistent with exposure age estimates for major ice recession from terminal moraine limits in the lower Pukaki Basin (Schaefer et al, 2006) and with evidence from throughout New Zealand for a major change in climate around 18,000 cal yr BP that terminated the last major glacial episode (Newnham et al, 2003(Newnham et al, , 2007aAlloway et al, 2007). Nevertheless, at Boundary Stream Tarn, absence of tall forest and dominance of subalpine shrubland and alpine grassland between 17,500 and 14,200 cal yr BP indicates that climate regimes were cooler and more extreme than at present.…”

Discontinuous late Pleistocene‐Holocene pollen records from Auckland Domain, northern New Zealand

“…The changes could be interpreted as a decline in conifer-hardwood forest, increased shrub/grassland and Fuscospora forest, and lowering of the water table in the crater wetland as a result of a change to a cooler and drier climate with a higher fire frequency (ignited by lightning). The timing of this according to the radiocarbon dates (i.e., after 47 000 yr BP) is consistent with other pollen records from the Auckland region which suggest that beech forest expanded c. 50 000 yr BP and remained dominant until around c. 20 000 yr BP (Lancashire et al 2002;Sandiford et al 2002Sandiford et al ,2003Shane & Sandiford 2003;Newnham et al 2007). From c. 23 000 to 16 500 yr BP, continued cooling restricted Auckland forest to patches within extensive shrubland/grassland.…”

“…These extinct basaltic maars or scoria cones, or a combination of both, erupted during the Pleistocene-Holocene. Several of the maar craters, Pukaki crater (Dickinson 2001;Sandiford et al 2001Sandiford et al , 2003, Onepoto Basin (Shane & Sandiford 2003), Lake Pupuke (Horrocks et al 2005a), kohuora crater (Newnham et al 2007), and the maars associated with the scoria cones of crater Hill (Lancashire et al 2002), Mt Richmond (Sandiford et al 2002), and McLaughlins Mountain (Horrocks et al 2007b), have recently been analysed for fossil pollen and tephra to provide vegetation histories (Fig. 1).…”

A revised age for the Kawakawa/Oruanui tephra, a key marker for the Last Glacial Maximum in New Zealand

“…The revision shifts the ages adopted for the timing and duration of climate events associated with the LGM (Vandergoes et al, 2005;Alloway et al, 2007;Newnham et al, 2007bNewnham et al, , 2012Augustinus et al, 2011;Barrell et al, in this issue). The revised KOT age will enable more accurate comparison of KOTbearing sedimentary archives with paleoclimate records that are dated independently of 14 C (e.g., via U/Th, 10 Be, or ice-core layer counting).…”