126 results for Lowe, David J., Journal article

  • Assessing drivers of plantation forest productivity on eroded and non-eroded soils in hilly land, eastern North Island, New Zealand

    Heaphy, Marie; Lowe, David J.; Palmer, David John; Jones, Hayden S.; Gielen, Gerty J. H. P.; Oliver, Graeme R.; Pearce, Stephen H. (2014-07-02)

    Journal article
    University of Waikato

    Methods: The impact of soil erosion by mass movement on forest productivity was investigated in a paired plot trial in a planted forest in a mainly hilly to steepland catchment (Pakuratahi) near Napier, eastern North Island, New Zealand. Tree growth and form were measured and soil properties analysed to compare productivity and productivity drivers in adjacent non-eroded and eroded plots. Background: The effect of soil erosion on New Zealand production forestry is not well known and there has been no research prior to our study into the relationship between soil nutrient status and planted forests growing in eroded soils in steeplands. Results: Regression analysis showed that the decreased soil total nitrogen, total carbon, total phosphorus, and soil organic matter content in eroded plots had a negative impact on tree volume, resulting in a 10% decrease in measured tree volume. Based on an assessment of log quality, trees in the eroded plots were forecast to produce 16% less volume from high-quality pruned logs (with associated reduction in revenue of around $4000 per hectare), than trees in non-eroded plots. The total recoverable volume (TRV), estimated (for a 25-year rotation) from the measured Pinus radiata D. Don trees growing on the eroded sites, was valued at $68,500, about 9% less than the estimated TRV from trees measured on non-eroded plots ($76,000). Tree form and mean tree height in eroded and non-eroded plots were not significantly different. Conclusions: Soil erosion impacts production in planted forests. Afforestation of erodible land provides a valuable ecosystem service through land and soil stabilisation but this service is currently not reflected in the market prices for timber in New Zealand. Maintaining the productive capacity of erodible soils through practices such as fertilisation or continuous-cover forestry can add further costs to production forestry. To ensure that sustainable forest practices are carried out to protect the productivity of soils, financial incentives may be justified.

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  • INTREPID Tephra-II: - 1307F

    Lowe, David J. (2013)

    Journal article
    University of Waikato

    The INTREPID Tephra project, “Enhancing tephrochronology as a global research tool through improved fingerprinting and correlation techniques and uncertainty modelling”, was an overarching project of the international community of tephrochronologists of the International Focus Group on Tephrochronology and Volcanism (INTAV), which in turn lies under the auspices of INQUA’s Stratigraphy and Chronology Commission (SACCOM). INTREPID’s main aim has been to advance our understanding and efficacy in fingerprinting, correlating, and dating techniques, and to evaluate and quantify uncertainty in tephrochronology, and thus enhance our ability to provide the best possible linking, dating and synchronising tool for a wide range of Quaternary research projects around the world. A second aim has been to re-build the global capability of tephrochronology for future research endeavours through mentoring and encouragement of emerging researchers in the discipline.

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  • "New Zealand Soil Classification” by A.E. Hewitt [Book review]

    Lowe, David J. (1992)

    Journal article
    University of Waikato

    The publication of `New Zealand Soil Classification' by Dr Alan Hewitt this year (Hewitt 1992a) represents a major milestone in New Zealand soil science. That it was one of the final publications of the now defunct DSIR is somehow appropriate because, as classification systems should, it provides (in a mere 133 pages) a synthesis of much of what has been learnt about the soils of New Zealand over the past 60 years or more, The new classification was officially launched at the New Zealand Society of Soil Science Conference in Rotorua on 16 November, 1992.

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  • Preface: Enhancing tephrochronology and its application (INTREPID project): Hiroshi Machida commemorative volume

    Lowe, David J.; Davies, Siwan M.; Moriwaki, Hiroshi; Pearce, Nicholas J.G.; Suzuki, Takehiko (2011)

    Journal article
    University of Waikato

    Tephrochronology is the characterization and use of tephras – the explosively-erupted, unconsolidated, pyroclastic products of volcanic eruptions – or cryptotephras (glass-shard and/or crystal concentrations not visible as layers) as a unique stratigraphic linking, synchronizing, and dating tool. The word ‘tephra’ is derived directly from the Greek word tephra meaning ‘ashes’. Although the method is founded in stratigraphy, tephrochronology relies also on characterizing or ‘fingerprinting’ inherent tephra-derived components using laboratory-based analysis to complement field-based evidence. Such analysis includes the petrographic identification of mineral assemblages and the geochemical assay of glass shards, melt inclusions, or crystals (minerals including plagioclase, olivine, pyroxenes, amphiboles, biotite, or Fe–Ti oxides such as titanomagnetite) using the electron microprobe and other instruments including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ( [Lowe, 2011] and [1] ). These data are supported by the derivation of numerical ages on tephras/cryptotephras using a range of techniques including radiometric (e.g., radiocarbon, fission track, luminescence), incremental (e.g., layering in ice cores, varves, dendrochronology), age-equivalence (e.g., orbital tuning, magnetopolarity, palynostratigraphy), relative dating (e.g., obsidan hydration), and historical observation. Ages are also obtained using Bayesian-based flexible depositional modelling and wiggle matching (e.g., [Lowe et al., 2007] and Lowe et al., 2008 D.J. Lowe, P.A.R. Shane, B.V. Alloway and R.M. Newnham, Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE.. Quaternary Science Reviews, 27 (2008), pp. 95–126. [Lowe et al., 2008] ).

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  • Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist

    Lowe, David J.; Tonkin, Philip J.; Neall, Vincent E.; Palmer, Alan S.; Alloway, Brent V.; Froggatt, Paul C. (2008)

    Journal article
    University of Waikato

    Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3).

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  • Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE

    Lowe, David J.; Shane, Phil A.R.; Alloway, Brent V.; Newnham, Rewi M. (2008-01)

    Journal article
    University of Waikato

    The role of tephras in the NZ-INTIMATE project is a critical one because most high-resolution palaeoclimatic records are linked and dated by one or more tephra layers. In this review, first we document eruptive, distributional, and compositional fingerprinting data, both mineralogical and geochemical, for 22 key marker tephras erupted since 30,000 years ago to facilitate their identification and correlation. We include new glass compositional data. The selected marker tephras comprise 10 from Taupo and nine from Okataina volcanoes (rhyolitic), one from Tuhua volcano (peralkaline rhyolitic), and one each from Tongariro and Egmont volcanoes (andesitic). Second, we use four approaches to develop 2σ-age models for the tephras (youngest to oldest): (1) calendar ages for Kaharoa and Taupo/Y were obtained by wiggle-matching log-derived tree-ring sequences dated by 14C; (2) Whakaipo/V was dated using an age–depth model from peat; (3) 14 tephras in the montane Kaipo peat sequence (Waimihia/S, Unit K, Whakatane, Tuhua, Mamaku, Rotoma, Opepe/E, Poronui/C, Karapiti/B, Okupata, Konini, Waiohau, Rotorua, Rerewhakaaitu) were dated by simultaneously wiggle-matching stratigraphic position and 51 independent 14C-age points against IntCal04 using Bayesian probability methods via both OxCal and Bpeat; and (4) the five oldest tephras, erupted before ca 18,000 cal. yr BP, were dated by calibrating limited numbers of 14C ages using IntCal04 (Okareka) or comparison curves of the expanded Cariaco Basin sequence (Te Rere, Kawakawa/Oruanui, Poihipi, Okaia). Kawakawa/Oruanui tephra, the most widely distributed marker tephra, was erupted probably ca 27,097±957 cal. yr BP. Potential dating approaches for the older tephras include their identification in Antarctic ice cores (if present) or annually laminated sediments for which robust calendar-age models have been constructed, high-precision AMS 14C dating on appropriate material from environmentally stable sites, systematic luminescence dating, or new radiometric techniques (e.g. U–Th/He) if suitable minerals are available and errors markedly reduced. Further application of Bayesian age-modelling to stratigraphic sequences of 14C ages, possibly augmented with luminescence ages, may help refine age models for pre-Holocene tephras with the largest errors. Finally, we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the New Zealand region, which is a key objective of Australasian and Southern Hemisphere INTIMATE projects.

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  • Globalization of tephrochronology: new views from Australasia

    Lowe, David J. (2008)

    Journal article
    University of Waikato

    Tephra (or volcanic ash) studies, once confined largely to volcanic lands, have become increasingly practised in countries far removed from areas of active or recent volcanism – and Australia is no exception. At the International Union for Quaternary Research (INQUA) conference in Cairns in July/August 2007, Sarah E. Coulter (née Davies), now a postdoctoral ice-core tephrochronologist at Queen’s University Belfast, reportedthe first occurrence of an exotic tephra in Australia in a core from Lynch’s Crater, Atherton Tableland, Queensland (Figure 1). The distal tephra, manifest as a tiny concentration of glass shards, was probably derived from a Papua New Guinean eruption around 75,000–80,000 years ago (S.E. Davies et al., 2007). Its value lies in providing a precise chronostratigraphic marker that potentially allows correlation of other long palaeoenvironmental sequences over wide distances. Davies’ study is but one of a revolutionary development in tephrochronology now focused on detecting diminutive, distal tephras that are invisible in the field and referred to as cryptotephras. From the Greek word kryptein, meaning ‘to hide’ (Hunt, 1999a; Hunt and Hill, 2001; Lowe and Hunt, 2001), cryptotephras typically comprise fine-ashsized (< ~100 μm) glass shards sparsely preserved and ‘hidden’ in peats or in lake, marine or aeolian sediments, or in ice cores (Figure 2). The cryptotephra theme is continued in section III, but beforehand nomenclature associated with the term ‘tephra’, which can be confusing and which sometimes is used incorrectly, is outlined.

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  • Test of AMS 14C dating of pollen concentrates using tephrochronology

    Newnham, Rewi M.; Vandergoes, Marcus J.; Garnett, Mark H.; Lowe, David J.; Prior, Christine; Almond, Peter C. (2007-01)

    Journal article
    University of Waikato

    Previous attempts to radiocarbon date sediments >10 kyr from the high rainfall region of Westland, New Zealand, a critical location for investigation of interhemispheric patterns of climate change, have been problematic. This study, building on recent work by Vandergoes and Prior (2003), shows that AMS 14C dating of pollen concentrates has potential to provide more reliable ages than other sediment constituents, including plant macrofossils. The method was applied to sediments from three sites containing the 22.6k 14C yr Kawakawa Tephra, which provided an independent test of the 14C ages. Although some minor laboratory contamination was detected in tests on background standards, the modelled relationship between sample mass and measured 14C content permitted an appropriate correction to be determined. Improved pollen concentrations derived by density separation between 1.4 and 1.2 specific gravity and sieving in the range 10-50 m provided either older ages than other fractions of the same sample or, where in situ contamination was not evident, equivalent ages. Differences in degree of in situ contamination between depositional environments indicated that, in Westland, lake sites may be less susceptible to contamination by younger carbon than peat sites, where this process may be facilitated by root penetration into underlying sediments.

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  • A review of late Quaternary silicic and some other tephra formations from New Zealand: their stratigraphy, nomenclature, distribution, volume, and age.

    Froggatt, Paul C.; Lowe, David J. (1990-01-01)

    Journal article
    University of Waikato

    The stratigraphic relationships and distribution of 36 named late Quaternary (≤c. 50 000 yr B P.) silicic tephra formations, erupted from 4 volcanic centres—Okataina, Taupo, Maroa, and Tuhua (Mayor Island)—are presented. The stratigraphy and status of several other named late Quaternary tephras are also discussed. This compilation brings together all the data, currently scattered through many publications, to make tephrostratigraphy more accessible and more easily used. The nomenclature of tephra formations is discussed and some rationalisations are suggested. The term “tephrology” is suggested as an appropriate title for the field of tephra studies. The deletion of grain-size (ash, lapi1li), shape (breccia), and lithologic (pumice) terms from all formation names is recommended, as is standardisation on a “Tephra Formation” formal Several tephra layers not previously formally named, or without designated type sections, are defined. The dominant ferromagnesian mineral assemblage of each tephra formation has been compiled as an aid to tephra identification. All available radiocarbon ages (384) on each tephra formation are presented, and each age is assessed for reliability in dating the eruption of that tephra. The standard-deviation weighted mean age of the reliable ages has been determined as the best current estimate of the age of each tephra. At least 10 tephra formations have no reliable ages, and efforts should be made to date these

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  • A new attraction-detachment model for explaining flow sliding in clay-rich tephras

    Kluger, Max O.; Moon, Vicki G.; Kreiter, Stefan; Lowe, David J.; Churchman, G.Jock; Hepp, Daniel A.; Seibel, David; Jorat, M. Ehsan; Mörz, Tobias (2017-02-01)

    Journal article
    University of Waikato

    Altered pyroclastic (tephra) deposits are highly susceptible to landsliding, leading to fatali-ties and property damage every year. Halloysite, a low-activity clay mineral, is commonly associated with landslide-prone layers within altered tephra successions, especially in depos-its with high sensitivity, which describes the post-failure strength loss. However, the precise role of halloysite in the development of sensitivity, and thus in sudden and unpredictable landsliding, is unknown. Here we show that an abundance of mushroom cap–shaped (MCS) spheroidal halloysite governs the development of sensitivity, and hence proneness to landslid-ing, in altered rhyolitic tephras, North Island, New Zealand. We found that a highly sensitive layer, which was involved in a flow slide, has a remarkably high content of aggregated MCS spheroids with substantial openings on one side. We suggest that short-range electrostatic and van der Waals interactions enabled the MCS spheroids to form interconnected aggre-gates by attraction between the edges of numerous paired silanol and aluminol sheets that are exposed in the openings and the convex silanol faces on the exterior surfaces of adjacent MCS spheroids. If these weak attractions are overcome during slope failure, multiple, weakly attracted MCS spheroids can be separated from one another, and the prevailing repulsion between exterior MCS surfaces results in a low remolded shear strength, a high sensitivity, and a high propensity for flow sliding. The evidence indicates that the attraction-detachment model explains the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding in sensitive, altered tephras rich in spheroidal halloysite.

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  • Advancing tephrochronology as a global dating tool: applications in volcanology, archaeology, and palaeoclimatic research

    Lane, C.S.; Lowe, David J.; Blockley, S.P.E.; Suzuki, T.; Smith, V.C. (2017)

    Journal article
    University of Waikato

    Layers of far-travelled volcanic ash (tephra) from explosive volcanic eruptions provide stratigraphic and numerical dating horizons in sedimentary and volcanic sequences. Such tephra layers may be dispersed over tens to thousands of kilometres from source, reaching far beyond individual volcanic regions. Tephrochronology is consequently a truly global dating tool, with applications increasingly widespread across a range of Quaternary and geoscience disciplines. This special issue of the International Focus Group on Tephrochronology and Volcanism (INTAV) showcases some of the many recent advances in tephrochronology, from methodological developments to diverse applications across volcanological, archaeological, and palaeoclimatological research.

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  • Correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods: review and evaluation

    Lowe, David J.; Pearce, Nicholas J.G.; Jorgensen, Murray A.; Kuehn, Stephen C.; Tryon, Christian A.; Hayward, Chris L. (2017)

    Journal article
    University of Waikato

    We define tephras and cryptotephras and their components (mainly ash-sized particles of glass ± crystals in distal deposits) and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental, geological, and archaeological research. We then document and appraise recent advances in analytical methods used to determine the major, minor, and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application. Protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures. A narrow electron beam (diameter ~3-5 μm) can now be used to analyze smaller glass shards than previously attainable. Reliable analyses of ‘microshards’ (defined here as glass shards <10 μm) can be subject to significant element fractionation during analysis, but the systematic relationship of such fractionation with glass composition suggests that analyses for some elements at these resolutions may be quantifiable. In undertaking analyses, either by microprobe or LA-ICP-MS, reference material data acquired using the same procedure, and preferably from the same analytical session, should be presented alongside new analytical data. In part 2 of the review, we describe, critically assess, and recommend ways in which tephras or cryptotephras can be correlated (in conjunction with other information) using numerical or statistical analyses of compositional data. Statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components (usually glass or crystals/phenocrysts) than heuristic alternatives. They enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations. In common with other scientific hypothesis testing, it is easier to infer using such analysis that two or more tephras are different rather than the same. Adding stratigraphic, chronological, spatial, or palaeoenvironmental data (i.e. multiple criteria) is usually necessary and allows for more robust correlations to be made. A two-stage approach is useful, the first focussed on differences in the mean composition of samples, or their range, which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures, similarity coefficients, hierarchical cluster analysis (informed by distance measures or similarity or cophenetic coefficients), and principal components analysis (PCA). Some statistical methods (cluster analysis, discriminant analysis) are referred to as ‘machine learning’ in the computing literature. The second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis. This stage may involve discriminant function analysis (DFA), support vector machines (SVMs), canonical variates analysis (CVA), and ANOVA or MANOVA (or its two-sample special case, the Hotelling two-sample T² test). Randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful. Compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices, hierarchical cluster analysis, and PCA. Such transformations may make the assumption of multivariate normality more appropriate. A sequential procedure using Mahalanobis distance and the Hotelling two-sample T² test is illustrated using glass major element data from trachytic to phonolitic Kenyan tephras. All these methods require a broad range of high-quality compositional data which can be used to compare ‘unknowns’ with reference (training) sets that are sufficiently complete to account for all possible correlatives, including tephras with heterogeneous glasses that contain multiple compositional groups. Currently, incomplete databases are tending to limit correlation efficacy. The development of an open, online global database to facilitate progress towards integrated, high-quality tephrostratigraphic frameworks for different regions is encouraged.

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  • Interpretation of pre-AD 472 Roman soils from physicochemical and mineralogical properties of buried tephric paleosols at Somma Vesuviana ruin, southwest Italy

    Inoue, Yudzuru; Baasansuren, Jamsranjav; Watanabe, Makiko; Kamei, Hiroyuki; Lowe, David J. (2009)

    Journal article
    University of Waikato

    This study aimed to interpret soil fertility around Somma Vesuviana in ancient Rome from investigation of buried paleosols developed beneath thick pumice deposits of the AD 472 Pollena eruption of Mt. Vesuvius. Two buried pedons derived mainly from phonolitic tephra deposits of the AD 79 Pompeii eruption, and ancient construction waste, were excavated and sampled at the Somma Vesuviana villa ruins on the northern flanks of Mt. Vesuvius, Italy. For comparison, a buried paleosol on equivalent Pompeii tephra deposits in a nearby forest, and a modern soil on AD 1631 tephra deposits (compositionally similar to Pompeii eruptives) in an adjacent orchard, were similarly analyzed for physical, chemical, and mineralogical properties, including phosphorus fractions and primary mineral compositions. The two buried pedons in the ruin had abundant available P and K and contained moderate amounts of exchangeable cations. Leucite was the dominant primary mineral and, with alkali feldspars, is probably the major source of K in the buried horizons. A high content of “authigenic P (Ca-bound P)” characterized all the pedons. We concluded that the buried Somma Vesuviana paleosols had a relatively high ability to supply nutrients and that they were fertile prior to the AD 472 eruption, although manuring to increase nitrogen was probably needed to maintain high productivity. Their physical properties such as water retention were probably enhanced by small but significant amounts of short-range order clays.

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  • A late-Holocene and prehistoric record of environmental change from Lake Waikaremoana, New Zealand

    Newnham, Rewi M.; Lowe, David J.; Matthews, Brent W. (1998)

    Journal article
    University of Waikato

    Further evidence in support of a late pre-European (Polynesian) settlement of New Zealand is provided by an 1850-year-long tephropalynological record from a remote region in New Zealand's North Island. The earliest unequivocally anthropogenic forest clearance is estimated from sedimentation rates to have occurred c. 375 14C years BP (c. ad 1523–1631), although the radiocarbon chronology, shown by tephrochron ology to be erroneous due to hard-water effects, suggested this occurred c. 900 years earlier. Delineation of the anthropogenic era, and the distinction between human activity and other agents of environmental change in the pollen/spore diagram, are supported by cluster analysis and detrended correspondence analysis. Two distinct phases of forest clearance are evident during the pre-European era, reflecting local changes either in population pressure or settlement patterns. We note that the lull between the two phases of forest clearance coincides with the maximum of the ‘Little Ice Age’ within the period c. late ad 1600s to early 1800s.

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  • Re-identification of c. 15 700 cal yr BP tephra bed at Kaipo Bog, eastern North Island: implications for dispersal of Rotorua and Puketarata tephra beds.

    Shane, Phil A.R.; Smith, Victoria C.; Lowe, David J.; Nairn, Ian A. (2003-12-01)

    Journal article
    University of Waikato

    A 10 mm thick, c. 15 700 calendar yr BP (c. 13 100 14C yr BP) rhyolitic tephra bed in the well-studied montane Kaipo Bog sequence of eastern North Island was previously correlated with Maroa-derived Puketarata Tephra. We revise this correlation to Okataina-derived Rotorua Tephra based on new compositional data from biotite phenocrysts and glass. The new correlation limits the known dispersal of Puketarata Tephra (sensu stricto, c. 16 800 cal yr BP) and eliminates requirements to either reassess its age or to invoke dual Puketarata eruptive events. Our data show that Rotorua Tephra comprises two glass-shard types: an early-erupted low-K2O type that was dispersed mostly to the northwest, and a high-K2O type dispersed mostly to the south and southeast, contemporary with late-stage lava extrusion. Late-stage Rotorua eruptives contain biotite that is enriched in FeO compared with biotite from Puketarata pyroclastics. The occurrence of Rotorua Tephra in Kaipo Bog (100 km from the source) substantially extends its known distribution to the southeast. Our analyses demonstrate that unrecognised syn-eruption compositional and dispersal changes can cause errors in fingerprinting tephra deposits. However, the compositional complexity, once recognised, provides additional fingerprinting criteria, and also documents magmatic and dispersal processes.

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  • A terrrestrial palynological record for the last two glacial cycles from southwestern New Zealand

    Newnham, Rewi M.; Vandergoes, Marcus J.; Hendy, Chris H.; Lowe, David J.; Preusser, F. (2007-02)

    Journal article
    University of Waikato

    A pollen profile from Okarito Pakihi Bog in south Westland, New Zealand extending from near present back to Marine Isotope Stage (MIS) 6 provides a continuous record of vegetation and climate change for the past two glacial cycles. Independent chronological control was obtained by AMS radiocarbon dating of organic sediments in the upper part of the sequence and OSL dating of inorganic silts in the lower part, with a unique tie point provided by the ca 26.5 cal ka Kawakawa Tephra. As was probably a common occurrence in this region, the basin developed as a moraine-dammed proglacial lake and remained lacustrine until the early Holocene, when a peat bog developed. Survival of the depositional site through subsequent multiple ice advances, unusual in a glaciated landscape, was probably assisted by lateral displacement of the basin relative to its source area, across the Alpine Fault. There is good correspondence between inferred periods of substantial treeline depression in the pollen profile and the record for ice advance in this region. More cooling events are evident in the pollen record, however, presumably due to the fragmentary nature of glacial geomorphology. The pollen record also shows broad consistency with the MIS record and hence with the Milankovitch orbital forcing model, but with some departures, including an early onset to the last glacial maximum (LGM). Several sub-Milankovitch scale events are also evident, including a mid-LGM warming and Lateglacial reversals during both the last and the penultimate deglaciation.

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  • Rerewhakaaitu Tephra, a land–sea marker for the Last Termination in New Zealand, with implications for global climate change

    Newnham, Rewi M.; Eden, Dennis N.; Lowe, David J.; Hendy, Chris H. (2003)

    Journal article
    University of Waikato

    The Rerewhakaaiutu Tephra erupted from Okataina Volcanic Centre, North Island, New Zealand, at 14,700±95 ¹⁴C yr BP (ca 17,600 cal yr BP) at a time of rapid re-organisation of Earth's climate system at the end of the Last Glacial (Termination I). It provides a distinctive isochron in a range of different environments in North Island and in adjacent South Pacific Ocean sediments. Terrestrial evidence, based on fluvial aggradation and downcutting relationships, loess accumulation rates, palaeovegetation patterns, and buried soil development and mineralogy, shows that marked amelioration of climate occurred shortly before the Rerewhakaaitu Tephra was deposited. Similarly, marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms, while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the Rerewhakaaitu Tephra. These changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms. The re-organisation of climate commencing at ca 15,000–14,500 ¹⁴C yr BP (ca 18,000–17,400 cal yr BP) is detected elsewhere in the Southern Hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres.

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  • Bayesian tools for tephrochronology

    Buck, Caitlin E.; Higham, Thomas F.G.; Lowe, David J. (2003)

    Journal article
    University of Waikato

    It is suggested that Bayesian statistical methods for radiocarbon data interpretation, already widely used in archaeology, also have potential to improve the dating of tephra layers and hence enhance their use for tephrochronology. By re-analysing data from a recently published paper in which the authors sought to identify the calendar date of the eruption of fourteenth-century AD Kaharoa Tephra, a key marker in New Zealand prehistory, it is shown that Bayesian methods can be used to draw together a coherent collection of radiocarbon data, undertake formal outlier detection, and include prior information. Regardless of the calibration curve adopted, the distribution of likely dates for the Kaharoa eruption is multimodal. By including prior information from wiggle-matched dendrochronology, the uncertainty on the estimate of the calendar date is reduced from a range of about 100 years to about 25 years (i.e., 648-623 cal. BP, with modes at 638 and 632 cal. BP). Using sensitivity analysis, however, it is shown that such estimates are affected by the quality and nature of the prior information available. As a result, we urge tephrochronologists to seek fastidiously both high-quality radiocarbon data and reliable stratigraphic sequences that might inform future geochronological model building.

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  • Late Quaternary volcanism in New Zealand: Towards an integrated record using distal airfall tephras in lakes and bogs

    Lowe, David J. (1988)

    Journal article
    University of Waikato

    Studies on distal airfall tephra layers preserved in lake sediments and peats in northern New Zealand have documented the stratigraphic, chronologic, and compositional relationships of 46 eruptives, aged c. 17000–700yr BP, which originated from six North Island volcanic centres: Taupo (9 tephras), Okataina (8), Maroa (1) (rhyolitic); Mayor Island (2) (peralkaline); Tongariro (11), Egmont (15) (andesitic). Sources were distinguished by mineralogy and composition, field relations, and 14C chronology. All known rhyolitic tephra-producing eruptions from Taupo, Okataina, and Maroa volcanoes since c. 17000yr BP are represented, but only a small proportion of the known tephras erupted from Tongariro, Egmont, or Mayor Island volcanoes is recorded. The distal tephras from these latter volcanic centres may thus reflect atypically powerful (or oblique) eruptions, or dispersal by strong winds. An improved record of volcanism for the Tongariro, Egmont, and Mayor Island centres might be obtainable from suitable lakes or bogs more proximal to them.

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  • Discriminant function analysis and correlation of Late Quaternary rhyolitic tephra deposits from Taupo and Okataina volcanoes, New Zealand, using glass shard major element composition

    Stokes, Stephen; Lowe, David J.; Froggatt, Paul C. (1992)

    Journal article
    University of Waikato

    Discriminant function analysis (DFA) is a multivariate statistical technique that provides a non-subjective means of correlating tephra deposits based on compositional or other variable characteristics. Using microprobe-determined glass shard major element composition, two DFA classification models were developed to separate (distinguish) individual tephra deposits erupted since ca. 22 ka from each of the rhyolitic Okataina and Taupo volcanoes, North Island, New Zealand. In an iterative approach, those tephras easily classified in the first DFA are removed from the dataset before applying the second DFA, hence generally improving the separation of the remaining tephras that are more closely alike. The first two canonical functions accounted for ca. 85% of variance within the Okataina dataset, and ca. 80% within the Taupo dataset. Using the first two canonical variates, we correctly classified 5 (Kaharoa, Rotoma, Waiohau, Rotorua, Te Rere) of the Okataina, and 4 (Taupo, Hatepe, Whakaipo, Karapiti) of the Taupo deposits under study, at efficiency levels of 70–100%. The incorporation of a third canonical variate, and additional sompositional data, would further improve our DFA models, which should ideally be used in conjunction with stratigraphic and other characteristic indices, where available, to facilitate accurate correlation. The Mahalanobis distance statistic (D²), a statistical measure of the multidimensional spacing of individual analyses, or groups of analyses, provides a better measure of likeness than the frequently used but subjective similarity coefficients technique.

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