New Zealand Journal of Geology
and Geophysics abstracts
Holocene vegetation,
environment, and tephra recorded from Lake
Pupuke, Auckland, New Zealand
Mark Horrocks1,2
Paul Augustinus2,3
Yanbin Deng4
Phil Shane3
Sofia Andersson5
1
Microfossil
Research Ltd
31 Mont Le Grand Rd, Mt Eden
Auckland, New Zealand
2School
of Geography & Environmental Science
University of Auckland
Private Bag 92 019
Auckland, New Zealand
3
Department of Geology
University of Auckland
4
School of Biological
Sciences
University of Auckland
5
Earth Sciences Centre
Göteborg University
S-405 30
Göteborg, Sweden
Abstract Lake
Pupuke provides a near-complete,
high-resolution environmental record of the Holocene from northern New
Zealand. Tephra beds constrain the timing of a range of proxy
indicators of environmental change, and demonstrate errors in a
radiocarbon chronology. Agathis
australis forest progressively
increases from c. 7000 yr BP and, in conjunction with indicators of
reduced biomass productivity, support a model of long-term climate
change to drier conditions over the Holocene. However, except for Agathis,
conifer-hardwood forest dominated mainly by Dacrydium
cupressinum
shows little change throughout the pre-human Holocene, suggesting
environmental stability. Dramatic vegetation change occurred only
within the last millennium as a result of large-scale Polynesian
deforestation by fire. This happened a short time before the local
eruption of c. 638 cal. yr BP Rangitoto Tephra. The identification of
two eruptions of tephra from Rangitoto volcano has implications for
future hazard planning in the Auckland region, because the volcanoes
were previously considered single event centres. Changes in atmospheric
circulation since the Late Glacial, possibly causing lower frequency of
distal ashfall in Auckland during the Holocene, complicates the use of
long-term records in hazard frequency assessment.
Keywords palynology;
tephrochronology;
geochemistry; 14C
dating; Holocene; Lake Pupuke; New
Zealand
G04004; Received 16 January
2004; accepted 27 April 2004; Online
publication date 23 March 2005
New Zealand Journal of Geology
& Geophysics, 2005, Vol. 48:
85–94
0028–8306/05/4801–0085 © The Royal Society of New Zealand 2005
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