Browsing by Author "Barbetti, M"

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    14C analyses at the ANTARES AMS Centre: dating the log coffins of northwest Thailand
    (Elsevier, 1994-06-03) Hotchkis, MAC; Fink, D; Jacobsen, GE; Lawson, EM; Shying, ME; Smith, AM; Tuniz, C; Barbetti, M; Grave, P; Quan, HM; Head, J
    Recent results of 14C analyses at the ANTARES AMS Centre are presented. Test measurements of 14C blanks demonstrate an ultimate sensitivity of the order of 10−15 (14C/12C ratio). Measurements of unknowns have been made with a precision in the range 1–1.5% using a “slow cycling” mode of operation where the injection magnet field is changed to inject 14C and 13C alternately. Results are presented for a series of log coffins from cave burials in NW Thailand. © 1994 Elsevier B.V.
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    The ANTARES AMS Centre : a status report
    (Cambridge University Press, 2016-07-18) Tuniz, C; Fink, D; Hotchkis, MAC; Jacobsen, GE; Lawson, EM; Smith, AM; Hua, Q; Drewer, P; Lee, P; Levchenko, VA; Bird, R; Boldeman, JW; Barbetti, M; Taylor, G; Head, J
    The ANTARES accelerator mass spectrometry facility at Lucas Heights Research Laboratory is operational and AMS measurements of 14C, 26Al and 36Cl are being carried out routinely. Measurement of 129I recently commenced and capabilities for other long-lived radioisotopes such as 10Be are being established. The overall aim of the facility is to develop advanced programs in Quaternary science, global climate change, biomedicine and nuclear safeguards. © the Department of Geosciences, The University of Arizona
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    Atmospheric 14C variations derived from tree rings during the early Younger Dryas
    (Elsevier, 2009-12) Hua, Q; Barbetti, M; Fink, D; Kaiser, KF; Friedrich, M; Kromer, B; Levchenko, VA; Zoppi, U; Smith, AM; Bertuch, F
    Atmospheric radiocarbon variations over the Younger Dryas interval, from ~13,000 to 11,600 cal yr BP, are of immense scientific interest because they reveal crucial information about the linkages between climate, ocean circulation and the carbon cycle. However, no direct and reliable atmospheric 14C records based on tree rings for the entire Younger Dryas have been available. In this paper, we present (1) high-precision 14C measurements on the extension of absolute tree-ring chronology from 12,400 to 12,560 cal yr BP and (2) high-precision, high-resolution atmospheric 14C record derived from a 617-yr-long tree-ring chronology of Huon pine from Tasmania, Australia, spanning the early Younger Dryas. The new tree-ring 14C records bridge the current gap in European tree-ring radiocarbon chronologies during the early Younger Dryas, linking the floating Lateglacial Pine record to the absolute tree-ring timescale. A continuous and reliable atmospheric 14C record for the past 14,000 cal yr BP including the Younger Dryas is now available. The new records indicate that the abrupt rise in atmospheric Δ14C associated with the Younger Dryas onset occurs at ~12,760 cal yr BP, ~240 yrs later than that recorded in Cariaco varves, with a smaller magnitude of ~40‰ followed by several centennial Δ14C variations of 20–25‰. Comparing the tree-ring Δ14C to marine-derived Δ14C and modelled Δ14C based on ice-core 10Be fluxes, we conclude that changes in ocean circulation were mainly responsible for the Younger Dryas onset, while a combination of changes in ocean circulation and 14C production rate were responsible for atmospheric Δ14C variations for the remainder of the Younger Dryas. © 2009, Elsevier Ltd.
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    Atmospheric radiocarbon for the period 1950-2010
    (Cambridge, 2013-01-01) Hua, Q; Barbetti, M; Rakowski, A Z
    We present a compilation of tropospheric (CO2)-C-14 for the period 1950-2010, based on published radiocarbon data from selected records of atmospheric CO2 sampling and tree-ring series. This compilation is a new version of the compilation by Hua and Barbetti (2004) and consists of yearly summer data sets for zonal, hemispheric, and global levels of atmospheric C-14. In addition, compiled (and extended) monthly data sets for 5 atmospheric zones (3 in the Northern Hemisphere and 2 in the Southern Hemisphere) are reported. The annual data sets are for use in regional and global carbon model calculations, while the extended monthly data sets serve as calibration curves for C-14 dating of recent, short-lived terrestrial organic materials. © 2013, Arizona Board of Regents on behalf of the University of Arizona
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    Building a future on knowledge from the past: what paleo-science can reveal about climate change and its potential impacts in Australia
    (Commonwealth Scientific and Industrial Research Organisation, 2005-06) Harle, KJ; Etheridge, DM; Whetton, P; Jones, R; Hennessy, K; Goodwin, ID; Brooke, BP; van Ommen, TD; Barbetti, M; Barrows, TT; Chappell, J; De Deckker, P; Fink, D; Gagan, MK; Haberle, SG; Heijnis, H; Henderson-Sellers, A; Hesse, PP; Hope, GS; Kershaw, P; Nicholls, N
    In Australia, high quality instrumental climate records only extend back to the late 19th century and therefore only provide us with a brief snapshot of our climate, its mean state and its short-term variability. Palaeo-records extend our knowledge of climate back beyond the instrumental record, providing us with the means of testing and improving our understanding of the nature and impacts of climate change and variability in Australia. There is a vast body of palaeo-records available for the Australian region (including Antarctica), ranging from continuous records of sub-decadal up to millennial scale (such as those derived from tree rings, speleothems, corals, ice cores, and lake and marine sediments) through to discontinuous records representing key periods in time (such as coastal deposits, palaeo-channels, glacial deposits and dunes). These records provide a large array of evidence of past atmospheric, terrestrial and marine environments and their varying interactions through time. There are a number of key ways in which this evidence can, in turn, be used to constrain uncertainties about climate change and its potential impacts in Australia.
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    Holocene marine 14C reservoir age variability: evidence from 230Th-dated corals in the South China Sea
    (American Geophysical Union, 2010-09) Yu, K; Hua, Q; Zhao, JX; Hodge, E; Fink, D; Barbetti, M
    The South China Sea (SCS) is well connected with the western Pacific and influenced by the East Asian monsoon. We have examined temporal variations in radiocarbon marine reservoir ages (R) and regional marine reservoir corrections (ΔR) of the SCS during the Holocene using paired measurements of AMS 14C and TIMS 230Th on 20 pristine corals. The results show large fluctuations in both R and ΔR values over the past 7500 years (yrs) with two distinct plateaus during 7.5–5.6 and 3.5–2.5 thousand calendar years before present (cal ka BP). The respective weighted mean ΔR values of these plateaus are 151 ± 85 and 89 ± 59 yrs, which are significantly higher than its modern value of −23 ± 52 yrs. This suggests that using a constant modern ΔR value to calibrate 14C dates of the SCS marine samples will introduce additional errors to the calibrated ages. Our results provide the first database for the Holocene R and ΔR values of the SCS for improved radiocarbon calibration of marine samples. We interpret the two ΔR plateaus as being related to two intervals with weakened El Niño - Southern Oscillation (ENSO) and intensified East Asian summer monsoon (EASM). This is because the 14C content of the SCS surface water is controlled by both the 14C concentration of the Pacific North Equatorial Current (NEC) which is in turn influenced by ENSO-induced upwelling along the Pacific equator and vertical upwelling within the SCS as a result of moisture transportation to midlatitude region to supply the EASM rainfall. © 2010 American Geophysical Union.
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    Influence of atmospheric circulation on regional (CO2)-C-14 differences.
    (American Geophysical Union, 2007-10-04) Hua, Q; Barbetti, M
    Detailed analyses of published C-14 data from tree rings and atmospheric CO2 samples for the northern tropics in Asia (India, Thailand, and Vietnam) and Africa (Ethiopia) have been performed for the heavily bomb-influenced period 1963-1967 A.D. The results show that the Asian summer monsoon and Intertropical Convergence Zone (ITCZ) position influenced atmospheric (CO2)-C-14 over the study area. Similar analyses of atmospheric records for northern and western Europe, northwestern Africa, and the northeastern United States and tree ring data for east Asia show that the Northern Hemisphere distribution of bomb C-14 for 1963-1967 depended on atmospheric circulation controlled by the seasonal positions of Hadley cell boundaries and the ITCZ. The distribution of C-14 did not have a simple latitudinal dependence. This work shows that the seasonal atmospheric circulation patterns are crucial for the description of atmospheric C-14 gradients during the bomb peak period. These principles can be applied to the interpretation of the small intrahemispheric C-14 offsets of the remote past. © 2007, American Geophysical Union
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    Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group
    (Wiley, 2006-10) Turney, CSM; Haberle, SG; Fink, D; Kershaw, AP; Barbetti, M; Barrows, TT; Black, M; Cohen, TJ; Corrège, T; Hesse, PP; Hua, Q; Johnston, R; Morgan, VI; Moss, PT; Nanson, GC; van Ommen, TD; Rule, S; Williams, NJ; Zhao, JX; D'Costa, D; Feng, YX; Gagan, MK; Mooney, SD; Xia, Q
    The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric ‘teleconnection’ and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. © 2006 John Wiley & Sons, Ltd.
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    Marine reservoir correction for the Cocos (Keeling) Islands, Indian Ocean
    (Cambridge University Press, 2004) Hua, Q; Woodroffe, CD; Barbetti, M; Smithers, SG; Zoppi, U; Fink, D
    Known-age corals from the Cocos (Keeling) Islands, Indian Ocean, have been analyzed by accelerator mass spectrometry (AMS) for radiocarbon to determine marine reservoir age corrections. The ΔR value for the Cocos (Keeling) Islands is 66 ± 12 yr based on the analyses undertaken for this study. When our AMS and previously published dates for Cocos are averaged, they yield a ΔR of 64 ± 15 yr. This is a significant revision of an earlier estimate of the ΔR value for the Cocos (Keeling) Islands of 186 ± 66 yr (Toggweiler et al. 1991). The (revised) lower ΔR for the Cocos (Keeling) Islands is consistent with GEOSECS 14C data for the Indian Ocean, and previously published bomb 14C data for the Red Sea, Gulf of Aden, and Cocos Islands. The revised ΔR is also close to values for the eastern Indian Ocean and adjacent seas. These suggest surface waters that reach the Cocos Islands might be partly derived from the far western Pacific, via the Indonesian throughflow, and might not be influenced by the southeast flow from the Arabian Sea. Copyright © The Arizona Board of Regents on behalf of the University of Arizona
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    Monsoonal influence on southern hemisphere (CO2)-C-14
    (American Geophysical Union, 2012-10-11) Hua, Q; Barbetti, M; Levchenko, VA; D'Arrigo, RD; Buckley, BM; Smith, AM
    Annual rings of a cross-dated teak tree core from Muna Island, Sulawesi, Indonesia in the southern equatorial tropics were analysed for radiocarbon from 1951-1979. C-14 levels at Muna started rising in 1956 and reached a maximum value of 667% in early 1965. The Muna Delta C-14 levels are significantly higher than those derived from the other Southern Hemisphere (SH) C-14 records (including tree rings and atmospheric CO2 sampling) for 1959 and 1963-1965. During the growing season of teak tree rings at this location (Nov-Apr) the Inter-tropical Convergence Zone (ITCZ) moves southward of Muna. Our results indicate that the island is strongly influenced by Northern Hemisphere (NH) air masses carried by the winter Asian monsoon, while the other more southerly SH sites remain covered by SH air masses. This monsoonal effect on atmospheric C-14 at Muna is evident during the periods of rapidly rising atmospheric C-14 (1959 and 1963-1965), when there is an enhanced C-14 contrast between northern and southern air masses. © 2012, American Geophysical Union.
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    New radiocarbon measurements from Tasmanian Huon pine: closing the current gap in tree-ring based calibration data for the early Younger Dryas
    (Eleventh International Conference on Accelerator Mass Spectrometry, 2008-09) Hua, Q; Barbetti, M; Fink, D; Levchenko, VA; Zoppi, U; Smith, AM; Bertuch, F
    The European absolute tree-ring chronologies have recently extended back to 12,594 cal BP [1], covering most of the Younger Dryas (YD). Radiocarbon data from these chronologies spanning the past 12,400 cal BP have been used to construct the younger part of the current internationally ratified calibration curve IntCal04 [2]. For the Late Glacial, radiocarbon data from a floating 1382-ring pine chronology are also available [3]. Here we present new high-precision, high-resolution radiocarbon measurements for the early YD chronozone derived from 4 sub-fossil logs of Huon pine with clearly defined annual tree rings. These logs were excavated from alluvial sediments along Stanley River in north-western Tasmania, Australia. A total of 137 samples, mostly decadal, were pretreated to alpha-cellulose, then converted to graphite and measured by AMS using the ANTARES facility at ANSTO [4], with a typical precision of 0.3-0.4%. A floating 617-ring Huon pine chronology has been constructed based on ring width and radiocarbon measurements. Our high-precision decadal 14C record, covering an age range from 10,350 to 10,760 14C years BP, has been linked to the European absolute tree-ring and floating Late Glacial Pine chronologies, bridging the current gap in the European tree-ring chronologies during the early YD and making a continuous and reliable atmospheric 14C record for the past 14,000 cal BP. Variations in atmospheric 14C during the YD recorded in tree rings and the possible mechanisms are also discussed. © The Authors
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    Radiocarbon in corals from the Cocos (Keeling) Islands and implications for Indian Ocean circulation
    (American Geophysical Union (AGU), 2005-11-02) Hua, Q; Woodroffe, CD; Smithers, SG; Barbetti, M; Fink, D
    Annual bands of a Porites coral from the Cocos (Keeling) Islands, eastern Indian Ocean, were analysed by radiocarbon for 1955–1985 AD. A rapid oceanic response of the site to bomb 14C is found, with a maximum Δ14C value of 132‰ in 1975. This value is considerably higher than those for the northwestern Indian Ocean, suggesting that surface waters reaching Cocos are not derived from the Arabian Sea. Instead, Δ14C values for Cocos and those for Watamu (Kenya) agree well over most of the study interval, suggesting that the South Equatorial Current carries 14C-elevated water rather than 14C-depleted water westward across the Indian Ocean. This implies that oceanic upwelling in the northwestern Indian Ocean is spatially confined with little contribution to the upper limb of the global thermohaline circulation. © 2005 by the American Geophysical Union.
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    Radiocarbon in tropical tree rings during the Little Ice Age
    (Elsevier, 2004-08) Hua, Q; Barbetti, M; Zoppi, U; Fink, D; Watanasak, M; Jacobsen, GE
    Cross-dated tree-ring cores (Pinus merkusii) from north-central Thailand, spanning AD 1620–1780, were used to investigate atmospheric 14C for the tropics during the latter part of the Little Ice Age. In addition, a cross-dated section of Huon pine from western Tasmania, covering the same period of time, was investigated. A total of 16 pairs of decadal samples were extracted to alpha-cellulose for AMS 14C analysis using the ANTARES facility at ANSTO. The 14C results from Thailand follow the trend of the southern hemisphere, rather than that of the northern hemisphere. This is a surprising result, and we infer that atmospheric 14C for north-central Thailand, at 17° N, was strongly influenced by the entrainment of southern hemisphere air parcels during the southwest Asian monsoon, when the Inter-Tropical Convergence Zone moves to the north of our sampling site. Such atmospheric transport and mixing are therefore considered to be one of the principal mechanisms for regional 14C offsets. © 2004 Elsevier B.V.
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    Radiocarbon variations from the Southern Hemisphere, 10,350–9700 cal BP
    (Elsevier, 2004-08) Barbetti, M; Hua, Q; Zoppi, U; Fink, D; Zhao, Y; Thomson, B
    We have made AMS measurements on a series of 10-ring samples from a subfossil Huon pine log found in western Tasmania (42°S, 145°E). The results show a pronounced rise in Δ14C over the first 200 years, and a decrease over the following 160 years. Tree-ring width measurements indicate that this log (catalogue SRT-447) can be cross-dated with another subfossil log (SRT-416) for which a series of high-precision radiometric 14C measurements have previously been made. When the two tree-ring series are thus aligned, SRT-447 is the older of the two logs, and there is a 139-year overlap. We then have a Huon pine floating chronology spanning 680 years, with 14C measurements attached. The 14C data sets agree well within the period of overlap indicated by the tree-rings. The 14C variations from Huon pine show excellent agreement with those from German oak and pine for the period 10,350–9670 cal BP. Aligning the Huon pine 14C series with that from German oak and pine allows us to examine the inter-hemispheric offset in 14C dates in the early Holocene. © 2004 Elsevier B.V.
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    Review of radiocarbon data from atmospheric and tree ring samples for the period 1945-1997 AD
    (Brill, 1999-01-01) Hua, Q; Barbetti, M; Worbes, M; Head, J
    A summary of 14C data from atmospheric sampling and measurements on wood from annual tree rings for the period 1945-1997 AD is presented and evaluated. Atmospheric records are characterized by different distributions of bomb-test 14C between the Northern and Southern Hemispheres, latitude dependence, and seasonal fluctuations. Radiocarbon data from tree rings are summarised and plotted against atmospheric records from similar latitudes. In some cases, discrepancies are found. Possible reasons for this include: 1) the use of stored carbohydrate from the previous year, 2) different 14C levels in the air around subcanopy trees due to respiration of CO2, 3) regional and local effects of anthropogenic CO2 and 14C sources, 4) sampling of wood material too close to ring boundaries, and 5) insufficient pretreatment of tree ring samples for dating. But in cases where trees were carefully selected and the samples adequately pretreated, radiocarbon data from tree rings show excellent agreement with direct atmospheric sampling records. © Brill 1999 (Open Access)
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    Use of AMS 14C dating to explore issues of occupation and demise at the medieval city of Angkor, Cambodia
    (Elsevier, 2007-03-05) Penny, D; Hua, Q; Pottier, C; Fletcher, R; Barbetti, M
    Angkorian temples are characterised by one or more encircling moats that are excavated into the alluvial substrate. As a key part of the overall design of the temple, the moats are important symbolically and are presumed to be contemporaneous with the associated temple. They also represent important depositional basins for sediment and other materials and can therefore yield vertical profiles of sediment that has accumulated since the moat was originally excavated. Unconformities in these moat profiles can be dated absolutely using small-sample, high-precision AMS radiocarbon techniques. These unconformities are likely to represent periodic re-excavation or maintenance of the moat and therefore indicate the presence of large, presumably centrally organised workforces. In some instances, presumed anthropogenic unconformities occur centuries after Angkor was supposedly abandoned. In this way, radiocarbon dates themselves are being used as a proxy indicator of cultural activity and are being used to challenge the historiography of Angkor’s famous demise. © 2007, Elsevier Ltd.
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    Variations in tree-ring 14C for the younger dryas
    (GNS Science, 2009-05-15) Hua, Q; Barbetti, M; Fink, D; Levchenko, VA; Zoppi, U; Smith, AM; Bertuch, F
    Of all millennial-scale paleoclimate reversals during the Last Glacial Cycle, the Younger Dryas (YD), from ~13 to 11.6 cal kyr BP, has attracted the most attention and controversy. The debate centres on understanding the physical mechanisms for such an abrupt change in climate and radiocarbon, which are associated with small changes in solar output and/or major changes in earth-system interactions dealing with oceanic circulation and exchanges between the carbon reservoirs. The leads and lags between climatic proxy records of the YD event are at the heart of such research. Unfortunately, one of the problems is that there is no reliable, direct atmospheric 14C record based on tree-ring chronology for the whole YD period, thus negating any possibility of locking in the critical time marker of its initiation. Here we present new high-precision, high-resolution radiocarbon measurements for the early YD chronozone derived from 4 sub-fossil logs of Huon pine with clearly defined annual tree rings. These logs were excavated from alluvial sediments along Stanley River in north-western Tasmania, Australia. A floating 617-ring Huon pine chronology has been constructed based on ring width and AMS radiocarbon measurements. Our 14C record, covering an age range from 10,350 to 10,760 14C years BP, has been linked to the European absolute tree-ring and floating Late Glacial Pine chronologies, bridging the current gap in the European tree-ring 14C chronologies during the early YD. A continuous and reliable atmospheric 14C record for the past 14 cal kyr BP is now available. This allows a more precise determination of the timing in observed climatic and environmental parameters and allows for a critical evaluation of mechanisms of atmospheric 14C variations for the YD.
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    Vegetation and land-use at Angkor, Cambodia: a dated pollen sequence from the Bakong temple moat
    (Cambridge University Press, 2006-09) Penny, D; Pottier, C; Fletcher, R; Barbetti, M; Fink, D; Hua, Q
    Investigating the use of land during the medieval period at the celebrated ceremonial area of Angkor, the authors took a soil column over 2.5m deep from the inner moat of the Bakong temple. The dated pollen sequence showed that the temple moat was dug in the eighth century AD and that the agriculture of the immediate area subsequently flourished. In the tenth century AD agriculture declined and the moat became choked with water-plants. It was at this time, according to historical documents, that a new centre at Phnom Bakeng was founded by Yasovarman I. © Antiquity Publications Ltd. 2006