REPORT FOR IMAGES SCI-COM, BREST 1999

Environmental Stability of Northeast New Zealand

Principal Material: IMAGES CORES MD972121 and MD972122

Personnel

Barbara Manighetti (Palaeoceanography): NIWA, Wellington, NZ
Mike Elliot (Palynology): NIWA, Wellington, NZ
Lionel Carter (Sedimentology): NIWA, Wellington, NZ
Lisa Northcote (Faunal studies): NIWA, Wellington, NZ
Gerald Ganssen (Paleoceanography): Free University, Amsterdam
Noel Trustrum (Terrestrial linkages): Landcare Research, NZ
Basil Gomez (Landscape studies): Indiana State University

Possible input also from:

Edouard Bard and associates (Alkenones) CEREGE
Ar-Ar dating/Igneous geochemists To be arranged

SUMMARY OF WORK IN PROGRESS

CORE MD972121

Depth: 2314 m, length: 35 m

Work to date indicates that this core has a fantastic record probably the best so far in the SW Pacific, and very promising for high resolution work back to approx. 150 ka. The sedimentation rate is high (average 25 cm/ka), and broad-scale isotopic profiles indicate a coherent sequence with no obvious disturbance. AMS dating of the top third of the core shows excellent integrity to 14C age sequence. Up to 90 (or more) tephras appear in the record, opening up the possibility of absolute dating of portions of the oxygen isotope curve. Most of the North Island NZ eruptives reaching the core site are from events of >1km3 volume, Plinian or Ultraplinian events, with some believed to be as large as 1000km3. Examination of the relationship of these gigantic volcanic events with local climate signals and comparison with the timing of regional/global change is just beginning, and may provide important new insights.

A draft paper is now complete (title: Palaeoclimatic, Source and Anthropogenic Influences on the Late Quaternary Sediment Flux off Eastern New Zealand) utilising high resolution sedimentological data from the core.

We have been carrying out palynological studies on the upper 1-1.5 m of the core, concentrating to date mainly on human deforestation/anthropogenic influence on the record over last 2000 years. The deforestation signal is very pronounced, indicating catastrophic impact of Polynesian settlement on the NZ landscape. A paper has been submitted to Nature, and NZ media interest is very strong.

We are currently engaged in analysis of the 'YD' interval, with the aim of establishing the timing and magnitude of any deglacial pause or reversal in S. Hemisphere marine records, and also to relate this to terrestrial signals via palynology. Faunal analysis for transfer function SST is underway, and may be supplemented in future by alkenone studies (Bard et al).

A paper is underway on the occurrence of a distinctive, peralkaline tephra layer at approx 7ka, more than doubling the maximum dispersal for this tephra reported to date. Peralkaline eruptives show promise as marker horizons, as they are much easier to distinguish than the numerous other rhyolitic tephras from the region.

CORE MD972122

Depth: 55 m, length: 16 m

This core offers a very high sedimentation rate record of nearshore processes and change. The core is 16 m long, and has a sedimentation rate of at least 100-150cm/ka. (Total record extends only to about 12ka stillstand of -56 m sea level). The pollen record for the top 3 m is now complete , and shows excellent coherence with the MD2121 record. A single AMS date on material from around the base of the deforestation signal (Polynesian settlement of NZ) is very close to the date recorded from 2121, and together these provide the first supporting evidence for the 'long prehistory' theory of settlement. Sufficient foraminiferal material is present that a good AMS chronology and isotopic curve should be possible, and there is potential for interesting examination of the frequency of cyclone events, changes in mean climatic conditions (?El Nino/La Nina cyclicity) and response of the terrestrial catchment to climate change during the Holocene.

Landcare Research and Indiana State University are also working on material from this core, and have been approached to report separately on their progress.

OTHER WORK

NIWA scientists are engaged in a range of projects with relevance to IMAGES goals, including investigation of physical and biological processes at ocean fronts (the Sub-Antarctic Front and Sub-Tropical Front lie close to the east of NZ), and ocean variability at widely varying temporal and spatial scales.

NIWA website: HYPERLINK http://www.niwa.cri.nz/