Stephen E.J. Swabey

University of Auckland

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Frank J. Berry

University of Birmingham

Alma Harris

Cardiff Metropolitan University

Trevor H. Worthy

Flinders University

C. T. Pillinger

The Open University

Thomas Smith

Institute of Geology and Geophysics

A. Conway

ConocoPhillips (United Kingdom)

P. A. Bland

Curtin University

Jez Higgins

Coventry (United Kingdom)

Cooperative Institutions

The Open University

Hong Kong Metropolitan University

Australian Museum

Planetary Science Institute

University of Birmingham

University of Kentucky

Azusa Pacific University

Technical University of Denmark

Instituto de Química Física Blas Cabrera

Consejo Superior de Investigaciones Científicas

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Calculating flux from meteorite decay rates: a discussion of problems encountered in deciphering a 10 ⁵ –10 ⁶ year integrated meteorite flux at Allan Hills and a new approach to pairing

Geological Society London Special Publications (1998)

P. A. Bland A. Conway Thomas Smith Frank J. Berry Stephen E.J. Swabey

Abstract Meteorite accumulation sites offer the prospect of observing changes in flux over time; however, two main problems must be overcome: calculating a decay constant for samples in an area, and providing accurate pairing data, such that the number of true meteorites (not fragments) can be ascertained. We have used a comparison of meteorite terrestrial age and weathering data to constrain decay constants for hot desert meteorite populations. Meteorites resident in these sites typically have terrestrial ages <50 ka. Our estimates of the flux of meteorites to the Earth are within a factor of 2–3 of independent estimates made by the Meteorite Observation and Recovery Project network, and suggest no change in the flux over the last 50 ka. A similar approach applied to meteorites from Allan Hills, Antarctica, finds much lower levels of weathering, although terrestrial ages for these samples are much longer. We also observe a correlation between terrestrial age and degree of weathering in the Allan Hills meteorites, suggesting a weathering rate 2–3 orders of magnitude slower than values typical of hot desert sites. Given that blue ice regions are subject to some horizontal flow, we propose a model in which the observed oxidation-terrestrial age distribution is largely a result of ice movement, rather than weathering. Comparing oxidation and terrestrial age data in the Antarctic and hot desert accumulations, we estimate a lifetime for the Allan Hills population of 200–300 ka. Given the distance to the nearest ice divide (200 km), this suggests an average horizontal flow rate of 1 m a −1 . This approach may allow an estimate of the catchment area for these samples to be made. In addition, we suggest an alternative method for pairing samples which makes use of automated image processing and data analysis of reflected light photomicrographs to acquire a ‘textural fingerprint’ of a sample, and a genetic algorithm to compare the numerous data variables.

10.1144/gsl.sp.1998.140.01.06

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Avifaunal changes revealed in Quaternary deposits near Waitomo Caves, North Island, New Zealand

Journal of the Royal Society of New Zealand (2002)

Trevor H. Worthy Stephen E.J. Swabey

Abstract Late Pleistocene (23 000–10 000 14C yr BP) and Holocene (10 000 14C yr – present BP) avifaunas are described from the Henry Lambert and associated passages in Gardners Gut Cave, Waitomo Caves, North Island, New Zealand. Nine radiocarbon dates on bones and three uranium series dates on speleothems support the dating of the sites. These data are augmented by six new dates and reanalysis of the avifaunas from F1c Cave, also in the Waitomo karst. A distinctive Pleistocene avifauna characterised by the moa Euryapteryx curtus and Pachyornis mappini and the North Island goose (Cnemiornis gracilis) with common associates including New Zealand coot (Fulica prisca), North Island takahe (Porphyrio mantelli), Finsch's duck (Euryanas finschi), and North Island kokako (Callaeas wilsoni) was present. The presence of kokako, saddleback (Philesturnus rufusater), and robin (Petroica longipes) in the Pleistocene deposits and the absence of grassland taxa such as pipit (Anthus novaeseelandiae) and quail (Coturnix novaezelandiae) indicate that the vegetation about Gardners Gut Cave included tall shrubland and probably lacked much grassland, even over the Last Glacial Maximum. The Holocene at Waitomo was characterised by a moa fauna dominated by Anomalopteryx didiformis, although both Euryapteryx curtus and Pachyornis mappini persisted in small numbers. The frequent occurrence of kakapo (Strigops habroptilus), weka (Gallirallus australis), and brown teal (Anas chlorotis) typifies Holocene avifaunas; Cnemiornis and Fulica are unknown from Holocene deposits in the area.

10.1080/03014223.2002.9517696

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Automated thresholding of active lavas using AVHRR data

International Journal of Remote Sensing (1995)

Alma Harris Stephen E.J. Swabey Jez Higgins

Abstract An automated algorithm for thresholding hot pixels in AVHRR data is presented. The algorithm, applied to cloud-free sub-images of channel 3 minus channel 4 brightness temperature, compares each target pixel with its immediate background and then compares this difference with the natural variation in the surrounding region. Application to images of Mount Etna identified thermally anomalous pixels containing active lava or vents.

10.1080/01431169508954654

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Citations (56)

The Nature of the Environment

New Zealand Geographer (2002)

Stephen E.J. Swabey

10.1111/j.1745-7939.2002.tb01624.x

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Rates of natural climate change : a study of speleothems

Stephen E.J. Swabey

Speleothems (cave calcite) provide many different proxy indicators for palaeoclimatic changes during the Quaternary era. Generally, the occurrence of growing speleothems is a strong proxy for global palaeoclimate, both geographically and through time. A database of speleothem U-Th ages shows some evidence for an early transition from the penultimate glacial to the last interglacial at -140 Ka BP. The database suggests an age of 63 Ka BP for the maximum cold period within isotope stage 4. Isotope stage 3 contains three periods of increased number of growing speleothems, at 40,50 and 56 Ka BP mainly in low latitude caves. The start of growth, growth rate, oxygen isotopes, carbon isotopes and luminescence intensity in two speleothems from southern Ireland provide high-resolution records of rapid palaeoclimate changes in that region during the Late Glacial. Several of these palaeoclimate proxies appear to be linked. The Younger Dryas (YO) cold event is dated at between 12.5 and 11.4 Ka BP in both speleothem records. The dominant agent of palaeoclimatic variation during the YD is probably changes in North Atlantic ocean circulation. A Microsoft Excel spreadsheet is developed as a means of rapidly converting between 14C and calendar years and vice versa.

Speleothem

Proxy (statistics)

Paleoclimatology

Marine isotope stage

10.21954/ou.ro.0000d519

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Citations (5)