Browsing by Author "Simon, KJ"

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    10Be concentrations in snow at Law Dome, Antarctica following the 29 October 20 and 20 January 2005 solar cosmic ray events
    (World Scientific, 2009-08) Pedro, JB; Smith, AM; Duldig, ML; Klekociuk, AR; Simon, KJ; Curran, MAJ; van Ommen, TD; Fink, D; Morgan, VI; Galton-Fenzi, BK
    Recent model calculations have attempted to quantify the contribution of major energetic solar cosmic ray (SCR) events to 10Be production.1,2 In this study we compare modeled 10Be production by SCR events to measured 10Be concentrations in a Law Dome snow pit record. The snow pit record spans 2.7 years, providing a quasi-monthly 10Be sampling resolution which overlaps with the SCR events of 29 Oct 2003 and 20 Jan 2005. These events were calculated to increase monthly 10Be production in the polar atmosphere (>65° S geomagnetic latitude) by ~60% and ~120% above the GCR background, respectively2. A strong peak in 10Be concentrations (>4σ above the 2.7 y mean value) was observed ~1 month after the 20 Jan 2005 event. By contrast, no signal in 10Be concentrations was observed following the weaker 29 Oct 2003 series of events. The concentration of 10Be in ice core records involves interplay between production, transport, and deposition processes. We used a particle dispersion model to assess vertical and meridional transport of aerosols from the lower stratosphere where SCR production of 10Be is expected to occur, to the troposphere from where deposition to the ice sheet occurs. Model results suggested that a coherent SCR production signal could be transported to the troposphere within weeks to months following both SCR events. We argue that only the 20 Jan 2005 SCR event was observed in measured concentrations due to favorable atmospheric transport, relatively high production yield compared to the 29 Oct 2003 event, and a relatively high level of precipitation in the Law Dome region in the month following the event. This result encourages further examination of SCR signals in 10Be ice core data. © 2009 World Scientific Publishing
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    15th International Conference on Accelerator Mass Spectrometry
    (Australian Nuclear Science and Technology Organisation, 2021-11-15) Bertuch, F; Child, DP; Fink, D; Fülöp, RH; Hotchkis, MAC; Hua, Q; Jacobsen, GE; Jenkinson, A; Levchenko, VA; Simon, KJ; Smith, AM; Wilcken, KM; Williams, AA; Williams, ML; Yang, B; Fallon, SJ; Wallner, T
    On behalf of the AMS-15 Organising committee, we would like to thank you for attending the 15th International Conference on Accelerator Mass Spectrometry. Held as an online event for the first time, the 2021 conference attracted over 300 attendees with presentations delivered by colleagues and professionals from around the globe.Applications of AMS to the world’s most pressing problems/questions: A-1 : Earth’s dynamic climate palaeoclimate studies, human impacts on climate, data for climate modelling. A-2 : Water resource sustainability groundwater dating, hydrology, water quality and management A-3 : Living landscapes soil production, carbon storage, erosion, sediment transport, geomorphology. A-4 : Catastrophic natural events volcanoes, cyclones, earthquakes, tsunamis, space weather, mass extinctions. A-5 : Advancing human health metabolic and bio-kinetic studies, bomb-pulse dating, diagnostics and bio-tracing. A-6 : Challenges of the nuclear age nuclear safeguards, nuclear forensics, nuclear waste management, nuclear site monitoring, impacts of nuclear accidents. A-7 :Understanding the human story archaeology, human evolution and migration, history, art and cultural heritage A-8 : Understanding the cosmos fundamental physics, nuclear astrophysics, nuclear physics AMS Research and Development: T-1 : Novel AMS systems, components and techniques T-2 : Suppression of isobars and other interferences T-3 : Ion sourcery T-4 : New AMS isotopes T-5 : Advances in sample preparation T-6 : Data quality and management T-7 : Facility Reports (Poster Presentation only)
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    36Cl exposure-age chronology of Late Pleistocene glaciations on Mount Tymphi, Pindus Mountains, northwest Greece
    (International Union for Quaternary Research (INQUA), 2019-07-27) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
    The mountains of Greece and the wider Balkans were glaciated during the Pleistocene. The most extensive glaciations occurred during the Middle Pleistocene when large ice caps and glaciers formed in several ranges including the Dinaric Alps and the Pindus Mountains. The Late Pleistocene in the Balkans, however, was characterised by smaller ice masses with glaciers restricted to the highest mountains. Nevertheless, these glaciers were important in shaping much of the high mountain landscapes that we see today and they supplied many rivers with outwash sediments. Here we present preliminary results from 36Cl terrestrial cosmogenic nuclide analyses. From samples collected in summer 2017, we have calculated exposure ages from moraine boulders and glaciated bedrock in the uppermost valleys and cirques of Mount Tymphi massif (2497 m) in northwest Greece. We address both a significant geographical gap in Mediterranean glacial chronologies and the temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene glacial record. Coupled with published U-series ages from lower elevation moraines, this is the first glacial chronology in the east-central Mediterranean based on multiple dating methods. On the southwest side of the massif, 18 exposure ages obtained from 3 moraines in the cirque and mouth of the Laccos Megalon Litharion valley and the mouth of the western cirque of Tsioumako (2155 m), indicate moraine formation between 1700 m and 2050 m a.s.l. during the Late Pleistocene. This complements previous U-series ages obtained from secondary calcites in glacial sediments below 1700 m (and elsewhere in the Balkans), which demonstrate more extensive glaciations dating to the Middle Pleistocene. At ~1430 m a.s.l. in the Laccos cirque on the northeast side of the massif, 6 exposure ages (5 boulders, 1 bedrock) from a pair of end moraines represent the first dates from this side of Mount Tymphi. They suggest small cirque glaciers persisted until at least the end of the Late Pleistocene, facilitated by avalanching snow and shading from the cliffs of Goura (2467 m). Understanding where, when and why glaciers reached their maxima during the last glacial cycle is not only important for understanding the dynamics of the glacial climate in this region, but also for the timing of sediment and meltwater delivery to river systems; the dynamics of Mediterranean refugia; and has implications for understanding the environmental context of nearby Middle and Upper Palaeolithic archaeological records.
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    Beryllium isotope signatures of ice shelves and sub-ice shelf circulation
    (Elsevier, 2019-01-01) White, DA; Fink, D; Post, AL; Simon, KJ; Galton-Fenzi, BK; Foster, S; Fujioka, T; Jeromson, MR; Blaxell, M; Yokoyama, Y
    Be isotopes are a useful tracer of sediment source and transport pathways but have not been widely tested in glacio-marine environments. We measured Be isotopes in a range of depositional environments from open marine, sub-ice shelf and subglacial settings throughout Prydz Bay, one of Antarctica's largest ice drainage systems. We find that strong sub-ice shelf and bottom current circulations can advect 10Be-rich open marine sediments into an ice shelf cavity, and 10Be-poor terrestrial sediments onto the continental shelf at the ice shelf outflow, meaning that 10Be concentrations reflect sub-ice shelf circulation patterns rather than depositional environment. However, HCl-extractable 10Be/9Be ratios can provide a more robust discrimination of sediment deposited in open marine and sub-ice shelf settings. Thus, Be isotopes are a useful tracer of both environmental setting and sub-ice shelf circulation strength in both modern and paleo-ice sheet margins. Crown Copyright © 2018 Published by Elsevier B.V.
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    Carbonate and silicate intercomparison materials for cosmogenic 36Cl measurements
    (Elsevier, 2019-09-15) Mechernich, S; Dunai, TJ; Binnie, SA; Goral, T; Heinze, S; Dewald, A; Schimmelpfennig, I; Keddadouche, K; Aumaître, G; Bourlès, D; Marrero, S; Wilcken, KM; Simon, KJ; Fink, D; Phillips, FM; Caffee, M; Gregory, LC; Phillips, R; Freeman, SPHT; Shanks, R; Sarikaya, MA; Pavetich, S; Rugel, G; Merchel, S; Akçar, N; Yesilyurt, S; Ivy-Ochs, S; Vockenhuber, C
    Two natural mineral separates, labeled CoCal-N and CoFsp-N, have been prepared to serve as intercomparison material (ICM) for in situ-produced cosmogenic 36Cl and natural chlorine (Clnat) analysis. The sample CoCal-N is derived from calcite crystals in a Namibian lag deposit, while the sample CoFsp-N is derived from a single crystal of alkali-feldspar from a Namibian pegmatite. The sample preparation took place at the University of Cologne and a rotating splitter was used to obtain homogeneous splits of both ICMs. Forty-five measurements of CoCal-N (between 1 and 16 per facility) and forty-four measurements of CoFsp-N (between 2 and 20 per facility) have been undertaken by ten target preparation laboratories measured by seven different AMS facilities. The internal laboratory scatter of the 36Cl concentrations indicates no overdispersion for half of the laboratories and 3.9 to 7.3% (1σ) overdispersion for the others. We show that the CoCal-N and CoFsp-N splits are homogeneous regarding their 36Cl and Clnat concentrations. The grand average (average calculated from the average of each laboratory) yields initial consensus 36Cl concentrations of (3.74 ± 0.10) × 106 at 36Cl/g (CoCal-N) and (2.93 ± 0.07) × 106 at 36Cl/g (CoFsp-N) at 95% confidence intervals. The coefficient of variation is 5.1% and 4.2% for CoCal-N and CoFsp-N, respectively. The Clnat concentration corresponds to the lower and intermediate range of typical rock samples with (0.73 ± 0.18) µg/g in CoCal-N and (73.9 ± 6.8) µg/g in CoFsp-N. We discuss the most relevant points of the sample preparation and measurement and the chlorine concentration calculation to further approach inter-laboratory comparability. We propose to use continuous measurements of the ICMs to provide a valuable quality control for future determination of 36Cl and Clnat concentrations. © 2019 Elsevier B.V.
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    Chemical removal of sulphur from AgCl and AgBr for 36Cl measurements at ANSTO
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Simon, KJ; Wilcken, KM; Amatya Joshi, A
    Measurements of 36Cl on the 6MV tandem accelerator (SIRIUS) at ANSTO began in 2016, and since then over 1000 groundwater and rock samples have been processed and measured. The challenge with the sample preparation for 36Cl is to keep the 36S rates consistently low to minimise the impact to the 36Cl ion detection. This is generally achieved by precipitating sulphate as BaSO4 before a final precipitation as AgCl. We tested a range of methods for their efficacy, ease of use and consistency in keeping the 36S rates low. For measurement, the AgCl is backed in a bed of AgBr, but the sulphur rate of commercially available AgBr can vary significantly between batches. Preparing AgBr in house can produce very low sulphur rates [1,2]. Alternatively, we have achieved similarly low 36S rates by treating commercially available AgBr in 1M HNO3 for >24 hours.
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    A cosmogenic glacial chronology of Lake Judd, southwest Tasmania and latitudinal shifts in the Roaring Forties
    (International Union for Quaternary Research (INQUA), 2019-07-27) Fink, D; Wilcken, KM; Simon, KJ; Schulmeister, J; Thackray, GD
    Limited attention has been paid to the glacial history of Tasmania (40-44 S). At the northern limits of today’s Westerly storm track (the Roaring Forties), it experiences precipitation changes due to shifts in the Southern Annular Mode and ITCZ. Cosmogenic dating in southwest Tasmania (Kiernan 2010) highlights the marginal nature of its glaciation where small precipitation or temperature changes cause large changes in mass balance. This makes southwestern Tasmania an excellent location to study Westerly flow through the Last Glacial Cycle. The prevailing idea is that during glacial times, Westerlies expand northward to lower Southern Ocean latitudes, delivering increased rainfall to Tasmania, whilst during interglacials, their migration polewards reduces precipitation. Somewhat counterintuitively, from a Tasmanian perspective of increased Westerly circulation and wind strength, maxima glaciation should coincide with peak global glacials. Although well preserved, extensive last glacial cycle moraine sequences are not common, a series of more than 20 terminal moraine ridges have been mapped over 3 km concentric with the southern margin of Lake Judd, in the SW wilderness corner of Tasmania. Morphologically, the Lake Judd sequence is believed to represent three phases; pre MIS-6, MIS 5-3 and MIS 2 (LGM), representing substantially different volumes of ice accumulation. Our first field campaign collected 16 dolerite samples (36Cl) from the three innermost concentric moraines adjacent to lake edge and 4 quartzite (10Be, 26Al) samples from the most distal moraines. Our aim is to test correlation of the long-term glacial history with records of westerly fluctuations from NZ speleothems (Whittaker et al., 2011) to determine whether the latitudinal variation in Westerly winds in the Australasian region are zonal during glacial times as they are demonstrated to be in interglacial intervals (Fletcher and Moreno, 2012). Preliminary exposure age calculations on the full set of 20 samples are in poor agreement with Kiernan’s age associations. The 10Be (and 26Al) ages on the distal moraine indicate a most probable MIS 4/5 affiliation (>50 ka), significantly younger than expected. In contrast, the 16 dolerite samples from the 3 innermost proximal moraines at lake edge gave a complex set of ages that ranged from MIS 3 to MIS 4 affiliation (45-25ka), somewhat older than predicted. To add further complexity, these 16 ages show no intra or inter moraine age trends with respect to their morphologic positions and ice flow direction. These results contrast with those from other Tasmanian glacial records and reveal the need for a concretive effort to apply cosmogenic exposure dating to the numerus glacial deposits already mapped throughout Tasmania.
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    Cosmogenic radionuclides as signatures of past Solar storm events
    (Australian National University, 2019-09-09) Smith, AM; Wilcken, KM; Simon, KJ; Dee, MW; Kuitems, M; Scifo, A; Moy, A; Curran, MAJ; Wallner, A; Fink, D; Fujioka, T
    This collaborative project examines the relationship between the ‘Carrington Event’ (CE), the largest solar storm of modern times, and two recently discovered cosmic radiation events of greater magnitude, the ‘Miyake Events’ (ME). The intention is to construct cosmogenic isotope (14C, 10Be and 36Cl) profiles across the CE, so they can be compared with similar data that have already been obtained for the ME. We will use ice cores from Law Dome, East Antarctica, collected under Australian Antarctic Science awards, for the 10Be and 36Cl analyses. The large diameter DSS0506 ice core will permit high-resolution measurements at ANSTO of 10Be and 36Cl across the CE. Furthermore, we also intend to measure 10Be and 36Cl in the main DSS ice core across the ME. These measurements will complement existing data as both isotopes will be measured in the same ice core for each event for the first time and at high temporal resolution. New tree rings spanning the CE and ME, sourced from the Oxford Dendrochronology Laboratory, have been measured for 14C at the University of Groningen at mostly annual resolution. The ultimate goal of this study is to determine whether or not all three events are manifestations of the same phenomena. A secondary goal is to provide a check on the independent DSS-main ice core chronology. The CE of 1859 is known from geomagnetic data and contemporary records of the aurorae, which were observed as far south as the tropics. The event predated ground-based neutron detectors and routine cosmogenic isotope measurement, so the intensity of the incident particle radiation is still a matter of conjecture. Indeed, this question has been thrown into sharp focus recently by new discoveries in palaeoastronomy. Analyses of natural archives (tree-rings and ice-cores) have revealed that production of the cosmogenic isotopes 14C, 10Be and 36Cl spiked dramatically in the years 774-775 AD and 993-994 AD. Such anomalies could only have been generated by sudden bursts of cosmic radiation. Several sources were initially proposed for the radiation, however, the consensus now is that they were driven by solar activity. Here we discuss progress with the measurement of the cosmogenic radioisotopes and consider how the relative production rates of the cosmogenic radioisotopes may be used to substantiate a solar cause for the historical radiation events and to infer the spectral hardness of the initiating solar protons. © The Authors.
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    Cosmogenic radionuclides at Law Dome, East Antarctica, as signatures of past Solar storm events.
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Smith, AM; Curran, MAJ; Fink, D; Dee, MW; Kuitems, M; Levchenko, VA; Moy, A; Scifo, A; Simon, KJ; Wilcken, KM
    This project investigates evidence for increased atmospheric production of cosmogenic radionuclides in ice core records at Law Dome, East Antarctica, during three extreme events. These events are the Carrington Event (CE) of 1859 AD [1], the largest solar storm of modern times, and two recently discovered cosmic radiation events of even greater magnitude, the Miyake Events (ME) of 774/5 AD [2] and 993/4 AD [3]. Our intention is to determine ¹⁴ C, ¹⁰ Be and ³⁶ Cl profiles, with the highest sub-annual temporal resolution to date, across these events to determine whether or not all three events are manifestations of the same phenomena. Understanding the frequency, origin and magnitude of these events is essential for future-proofing modern communication infrastructure against such high magnitude radiation impacts from space. Identification of the events also provides an independent check on the Law Dome ice chronology. New annual Δ¹⁴ C measurements in tree rings, in combination with earlier published data, show that the ME774 and the ME993 events occurred in close proximity to the point of maximum activity of the 11-year solar cycle [4]. Although it did not leave any radiocarbon signature, the CE1859 event was already known to have occurred around the point of maximum activity of the solar cycle from sunspot records. Ice samples for ¹⁰ Be and ³⁶ Cl analysis are derived from ice cores drilled near the summit of Law Dome, East Antarctica. This is the first time these radionuclides have been measured at the same site for these events, allowing a direct comparison of ME774, ME993 and CE1859 under similar transport conditions. Both ME samples were taken from sections of core where the amount of available ice was limited, and the CE samples were taken from a section where more ice was available. AMS measurements involved some method development at ANSTO, measuring both ¹⁰ Be and ³⁶ Cl in the same samples, with sample sizes challenging for the ME samples. Preliminary ¹⁰ Be results at annual resolution spanning 30 years allowed an exact location of the events. We have clearly identified the expected ME774 and ME993 ¹⁰ Be peaks, which were ~ 4 years and ~ 2 years, respectively, within the error of when the layer-counted DSS ice core chronology had suggested. Accordingly, a further set of ¹⁰ Be samples at sub-annual seasonal resolution have been taken to better define the fine structure and amplitude of the signal but are currently not processed. We will also prepare a set of ³⁶ Cl AMS targets from the sub-annual ice core samples and the initial annual survey samples. No discernible ¹⁰ Be peak or ³⁶ Cl peak was found for CE1859 at annual resolution. © The Authors
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    The distribution and fractionation of beryllium isotopes in various reactive phases of Antarctic marine sediments
    (Australian Nuclear Science and Technology Organisation, 2021-11) Jeromson, MR; Fujioka, T; Fink, D; Post, A; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DA
    Beryllium isotopes, ¹⁰ Be and ⁹ Be, in Antarctic marine sediments are increasingly being applied as paleoenvironmental proxies and indicators of past ice shelf extent. The evidence base for interpreting meteoric-¹⁰ Be concentrations and ¹⁰ Be/⁹ Be ratios has largely been derived from examining their spatial distribution in modern depositional environments, or by correlation with other proxies in paleo-records, such as diatom abundance. Meteoric-¹⁰ Be is geochemically adsorbed onto sediment grains in the reactive phase during transport from the atmosphere to deposition on the seafloor. Unlike meteoric-¹⁰ Be, ⁹ Be is both available within the reactive phase after crustal weathering and native within mineral lattice in significant quantities. The complexity in fixing and preserving the Be isotopes onto grain surfaces leads to uncertainties in selecting the chemistry methods to consistently extract the reactive phases of ¹⁰ Be and ⁹ Be in different sediments. This gap in understanding the physical behaviour and geochemical forms of reactive Be in Antarctic sediments limits their utility in reconstruction of paleoenvironmental conditions. We conducted a sequential leach procedure on three homogenised sediment grab samples from the front of the Amery Ice Shelf that span a range of water masses. Using different chemical reagents, from very weak to very strong, five phases of Be isotope signatures were extracted sequentially, including : i) water soluble, ii) amorphous oxides leached by 0.5M HCl, iii) crystalline oxides leached by 1M NH₂ OH-HCl in 1M HCl, iv) organic leached by 0.01M HNO₃ and H₂ O₂ , and v) mineral/residual phase dissolved by HF– with the water through to organic leach making the reactive phase. We found that the amorphous and crystalline oxide phases contained the largest fraction of ¹⁰ Be, about 90% of total ¹⁰ Be, with the remaining 10% being in the mineral/residual phase. For ⁹ Be, the oxide phases contained only 10-30%, the majority of ⁹ Be being in the residual phase. The water-soluble and organic chemical treatments were inefficient in extracting any significant reactive Be. This distribution has been observed in other deep marine and continental riverine sediments. However, the proportional distribution of the two isotopes between the amorphous and crystalline oxides differed for our Antarctic sediments compared to those other studies. While reactive ⁹ Be was close to equally split across the two oxide phases, 80% of reactive ¹⁰ Be was located within the amorphous phase, with the remainder within the crystalline oxide phase. The difference in fractionation provides evidence for different sources of each isotope and different processes affecting their deposition. ⁹ Be is sourced primarily from the Earth’s crust and is likely segregated into the different fractions during the process of subglacial chemical weathering. Open water ¹⁰ Be is processed in the water column, where interaction with biogeochemical processes likely segregates it into the more labile phases. These findings inform decisions regarding the selection of procedures for efficient and reproducible extraction of meteoric-¹⁰ Be, and for understanding the processes that drive the source and distribution of different isotopes around ice shelf systems. © The Authors
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    Extracting 10Be and 9Be from Antarctic marine sediments – a comparison of different extraction techniques
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Jeromson, MR; Fujioka, T; Fink, D; Post, AL; Simon, KJ; Sánchez-Palacios, JT; Blaxell, M; Enge, TG; Wilcken, KM; White, DA
    Application of meteoric-¹⁰ Be (M¹⁰ Be) in sediments and soils from diverse geomorphic settings has been active for many decades. In some cases, M¹⁰ Be is normalized by the reactive ⁹ Be from the same sediment sample. Given the complexities in geochemical pathways that M¹⁰ Be is incorporated in the reactive mineral phase of such sediments, very different Be isotope chemistry extraction techniques have been developed. Measurement of M¹⁰ Be and the reactive phase of ⁹ Be in coastal Antarctic marine sediments has increasingly become promising as a paleo-proxy for the presence (or absence) of past ice shelves, and/or subglacial meltwater discharge from grounded outlet glaciers draining the ice sheet. However, published works select different methods to chemically leach Be isotopes from the reactive phase of Antarctic marine sediment and few studies have quantitively compared the efficacy of different leaching recipes. This is problematic because comparisons of ¹⁰ Be/⁹ Be ratios across different Antarctic sites assumes the same chemical fractionation of Be isotopes regardless of the leaching method. We examined three large-volume sediment grabs from near the Amery Ice Shelf front in East Antarctica that represent a range of grainsize and environmental conditions. For Be extraction, homogenised materials from each of the three samples were treated with four different leaching procedures, 1–3 targeting the reactive phase: 1) 6M HCl; 2) 0.5M HCl followed by 1M hydroxylamine hydrochloride in 1M HCl; 3) 0.04M hydroxylamine hydrochloride in 25% acetic acid solution 4) a total extraction dissolving in HF, HNO₃ , and HClO₄ . We also selected one grab to assess the effect of grainsize within the following fractions: <38 um, 38–63 um, 63–90 um, 90–125 um, and >125 um. Each fraction was leached with 6M HCl for 24 hours at room temperature. We found that both the 6M HCl and the 1M hydroxylamine procedures leached the same amount of ¹⁰ Be as the total extraction, while the 0.04M hydroxylamine treatment leached only two thirds. Interestingly, the 6M HCl and the 0.04M hydroxylamine procedures leached the same relative proportion of ⁹ Be to ¹⁰ Be, and thus gave the same ¹⁰ Be/⁹ Be ratio, while the 1M hydroxylamine procedure leached relatively more ⁹ Be in relation to ¹⁰ Be, resulting in a lower ¹⁰ Be/⁹ Be than the other two methods. As shown in previous studies, our results indicate that Be-isotope concentrations varied inversely with grainsize, in our case increasing 4- fold from coarsest to finest fractions, critically showing that the ¹⁰ Be/⁹ Be ratio remained constant across all grainsizes. Hence, grainsize can be normalised by applying the reactive ¹⁰ Be/⁹ Be ratio. We conclude that differences in leaching procedures, can lead to significant variations in efficiencies in extracting Be isotopes from the reactive phase of sediment, whereas the ¹⁰ Be/⁹ Be ratio appears to remain the same. This study highlights the importance of careful method selection and its consistent application to allow for comparison between studies and more robust interpretation.
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    Facility report : ANSTO’s 6 MV NEC SIRIUS accelerator – an update since AMS 14 Ottawa
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Fink, D; Fülöp, RH; Fujioka, T; Kotevski, S; Simon, KJ; Wilcken, KM
    ANSTO’s SIRIUS tandem accelerator is a customised 6 MV tandem accelerator manufactured by NEC and commissioned in 2015. It is a shared AMS and IBA instrument described in detail in Pastuovic et al (2015). Initial AMS performance data for cosmogenic isotopes 10Be, 26Al and 36Cl was presented at the Ottawa AMS14 Conference (Wilcken et al 2019). The AMS spectrometer consists of a 134 sample-wheel MC-SNICS Cs sputter source, a 45-degree spherical ESA (R=300 mm) and a double focusing insulated injection magnet (R=1000 mm, ME=20, vacuum gap = 70 mm). Two stripper gases (typically Ar and He) and thin foils are selectable in the terminal, and the selected charge state is focussed by an in tank electrostatic quadruple triplet positioned in the high energy column section. The high-energy section consists of two identical ME=176 analysing magnets (R=1270 mm) feeding two independent beam line transport systems, one for AMS and the other IBA. The AMS setup includes a post-stripper or energy degrader ladder, a 45-degree spherical ESA (R=3810 mm, gap = 30mm) and two magnetic quadrupoles. A choice of 3 AMS beam lines selectable by a ±30 degree switcher magnet provides options for dedicated radionuclide detection of 10Be (absorber cell), 36Cl and 26Al (multi-anode ionization counter), and an 8 m long TOF setup for future 129I and U-isotope measurements. A suite of sample geochemistry preparation laboratories, including a dedicated laboratory for preparation of in-situ 14C samples ( Fulop et al 2019) and an ice-core storage facility, provide AMS targets of 10Be (meteoric), 10Be, 26Al 14C and 36Cl (in-situ). The cosmogenic chemistry extraction laboratories host many visiting students and researchers to prepare samples and participate in AMS measurements. A wide variety of earth science applications in landscape evolution, sediment transport, tectonics, polar ice sheet stability, Quaternary geochronology supporting paleoclimate research change, solar variability and archaeology are supported. Ancillary facilities at ANSTO provide high precision elemental analyses (eg 9Be and 27Al) using a variety of techniques (ICP-OES, ICP-MS, AA, SEM, and XRF). We present details of recent data on routine AMS accelerator performance, reproducibility and linearity with various AMS standards, transmission, sample throughput, background reduction, and some improvements in sample chemistry methods.
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    Groundwater tracing with nucleogenic 36Cl in West Canning Basin, Western Australia
    (European Geosciences Union, 2017-04-26) Wilcken, KM; Cendón, DI; Meredith, KT; Simon, KJ; Stopic, A; Peterson, MA; Hankin, SI
    Chlorine-36 has been used over the past 20-30 years as a groundwater tracer in many hydrological studies and is a well-established dating technique. Given the half-life of 301 kyr it is well suited for dating of ‘old’ groundwater between 50 kyr - 1 Myr. A challenge associated with utilising 36Cl as a tracer is that it can be produced via three different pathways that will influence the result based on the unique hydrogeological setting of a study area. Typically the dominant source of 36Cl in groundwater is atmospheric 36Cl that is produced at troposphere and stratosphere via interaction of cosmic-ray protons and secondary neutrons with Ar. However, the secondary cosmic-ray neutrons can similarly produce 36Cl in surface rocks particularly at high elevations. Also nucleogenic production of 36Cl at subsurface environments can become significant, especially if U and/or Th concentrations are high. Delineating and quantifying these processes is essential when using 36Cl as a groundwater dating tool. In contrast to a conservative situation where atmospheric 36Cl dominates, we present a study in the West Canning Basin located in the Pilbara region of Western Australia, where the 36Cl/Cl ratio increases from 30 10-15 near the recharge zone to 100 10-15 over a 60 km of flow path within a confined aquifer. Additional isotopic evidence (14C and 87Sr/86Sr) in groundwater, mineralogy (X-Ray diffraction) and elemental analysis (Neutron Activation) of whole-rock powder samples from the aquifer and overlying geological units, is used to establish an interpretation that nucleogenic 36Cl production is effectively the only potential process to explain the data. Nucleogenic production can influence the groundwater 36Cl content in two different ways: (1) as an additional input of Cl with a 36Cl/Cl ratio that reflects the neutron flux within the particular mineralogy; or (2) via “in-situ” production of 36Cl directly in the groundwater from the dissolved 35Cl where the rate is dictated by the neutron flux in the aquifer and the residence time. For this study, the whole-rock elemental composition is used to calculate the nucleogenic production within the aquifer and confining units of the groundwater system. This effectively ruled out both the Wallal sandstone aquifer and the overlying confining unit of the Jarlemai clay aquitard as the sources of 36Cl. Here we explore the idea that the underlying granite is the most likely source of 36Cl. © Author(s) 2017. CC Attribution 3.0 License.
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    High-resolution records of the beryllium-10 solar activity proxy in ice from Law Dome, East Antarctica: measurement, reproducibility and principal trends
    (Copernicus Publications, 2011-07-12) Pedro, JB; Smith, AM; Simon, KJ; van Ommen, TD; Curran, MAJ
    Three near-monthly resolution 10Be records are presented from the Dome Summit South (DSS) ice core site, Law Dome, East Antarctica. The chemical preparation and Accelerator Mass Spectrometer (AMS) measurement of these records is described. The reproducibility of 10Be records at DSS is assessed through intercomparison of the ice core data with data from two previously published and contemporaneous snow pits. We find generally good agreement between the five records, comparable to that observed between other trace chemical records from the site. This result allays concerns raised by a previous Antarctic study (Moraal et al., 2005) about poor reproducibility of ice core 10Be records. A single composite series is constructed from the three ice cores providing a monthly-resolved record of 10Be concentrations at DSS over the past decade (1999 to 2009). To our knowledge, this is the first published ice core data spanning the recent exceptional solar minimum of solar cycle 23. 10Be concentrations are significantly correlated to the cosmic ray flux recorded by the McMurdo neutron monitor (rxy = 0.64, with 95 % CI of 0.53 to 0.71), suggesting that solar modulation of the atmospheric production rate may explain up to ~40 % of the variance in 10Be concentrations at DSS. Sharp concentration peaks occur in most years during the summer-to-autumn, possibly caused by stratospheric incursions. Our results underscore the presence of both production and meteorological signals in ice core 10Be data. © Author(s) 2011.
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    The Last Glacial transition and Holocene ecological change in Arthur’s Pass National Park, New Zealand
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Adams, PM; Fink, D; Shulmeister, J; Woodward, C; Fujioka, T; Simon, KJ
    This study improves our understanding of paleo-climate and -environmental change in the high-country South Island New Zealand focusing on formerly glaciated valleys near Arthur’s Pass. The area is of importance being positioned under a steep precipitation gradient on the lee side of the Southern Alps. Be-10 exposure ages (n=37) of ice limits, mapped as terminal moraines deposited during the last deglaciation through to late Holocene, span the past 17 000 years. The glacial record from well-preserved moraine sequences within the valley floor and glacial benches (850 to 1350m) demonstrates an initial post-LGM fast retreat that confirms previous studies (e.g. Shulmeister et al., 2010). Coupled with available in-valley exposure ages from Misery, Dobson and McGrath Moraines (Fink et al, 2017), a comprehensive regional deglacial pattern emerges. The Be-10 ages at Misery Moraines, subject of an early debate supporting a Younger Dryas glacial advance in the Southern Hemisphere (Ivy-Ochs et al. (1999), are re-dated to the Antarctic Cold Reversal (~14-15 ka). The record in headwater valleys of the Bealey and Otira rivers is largely obscured by slope-processes making conclusive observations relating to glaciation difficult. Consequently, early to middle Holocene moraines ages were not recovered in these valleys in contrast to nearby Dart Valley (Dowling et al., 2021). There is strong evidence at Otira headwall for a Little Ice Age glacial moraine limit. Several non-glacial boulders yield ages of 6.7ka, 4.2ka, 2.2ka and 1.7ka in the over steepened upper reaches of Bealey and Otira valleys that may reflect landslides associated with separate seismic events. In addition to our glacial chronology, we report on a well constrained record from Lances Tarn (Pb-210, and 37 radiocarbon dates over 4 m core length), a moraine-impounded bog at the saddle of Arthur’s Pass. This record spans ~13 000 years and displays post-glacial environmental change. The pollen record indicates typical succession from herb field through to closed forest, similar to other regional records (e.g. McGlone et al., 2004). The onset of Holocene like conditions is observed early c12ka, unlike central and lower South Island (~10ka). The area is influenced by persistent westerly flows through the entire record but with a reduction in flow in Early Holocene between 9.5 and 8.5ka, causing drier conditions in agreement with other records in Tasmania (Mariani and Fletcher, 2017 also in Patagonia (Moreno et al., 2020). There is little evidence of burning until c2.2ka when grass pollen rises sharply and charcoal counts increase, indicating a change in evapotranspiration (drying). Increased fires are evident from the onset of human arrival 750 years ago. The largest change in fire history and sediment transport occurs after European settlement ~ 1850’s, when intensive deforestation is evident in the pollen record. © The Authors
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    Late Pleistocene glacial chronologies in the Balkans: new 36Cl exposure-age dating from Montenegro and Greece
    (Copernicus GmbH, 2020-05-04) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM; Tomkins, M
    The timing and extent of mountain glaciation during the Late Pleistocene shows considerable variability around the world. Identifying the nature and timing of glaciation is important for understanding landscape evolution and changing climatic conditions (precipitation and temperature). In the Balkans, glaciers were actually larger during the Middle Pleistocene when large ice caps formed in several mountain ranges including the Dinaric Alps, Montenegro, and the Pindus Mountains, Greece. Glaciations younger than Marine Isotope Stage 6 were characterised by smaller ice masses with glaciers mainly restricted to the highest mountains. The behaviour of Late Pleistocene glaciers in this region influenced the timing of sediment and meltwater delivery to river systems; the migration of modern humans across Europe; and the dynamics of biological refugia. However, dating control is limited for Late Pleistocene glaciers in the Balkans. Here we report new in-situ 36Cl terrestrial cosmogenic nuclide exposure ages from moraine boulders sampled in the Velika Kalica valley, in the Durmitor massif, Montenegro. This valley was targeted because it contains the Debeli Namet glacier - the last remaining glacier in Montenegro. We have sampled 25 limestone boulders from 5 moraines situated down-valley of the current glacier at altitudes between 1650–2000 m. AgCl targets for 36Cl assay were prepared at The University of Manchester and 36Cl concentrations were measured on the SIRIUS 6MV accelerator at the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation. At the last local glacial maximum, the Debeli Namet glacier extended almost 3 km beyond its current position. These 36Cl analyses are part of a wider regional Mediterranean study, totalling >50 new exposure ages, which also includes Mount Tymphi in the Pindus Mountains, NW Greece. The project will address both a significant spatial and temporal gap in Mediterranean glacial chronologies by targeting the hitherto undated Late Pleistocene glacial record. The work in Montenegro will also shed light on the nature of Holocene glaciation in the Balkans. © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 Licence.
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    Late Pleistocene glaciers in Greece: a new 36Cl chronology
    (Elsevier, 2020-10-01) Allard, JL; Hughes, PD; Woodward, JC; Fink, D; Simon, KJ; Wilcken, KM
    Glaciers formed in the highest mountains of Greece during the Late Pleistocene, but the timing of glacier maxima is poorly understood. This paper presents 27 36Cl terrestrial cosmogenic nuclide exposure ages from glacial boulders on Mount Tymphi (2497 m a.s.l., 40oN) in Epirus, northwest Greece. These ages address both a significant geographical gap in Mediterranean glacial chronologies and a temporal gap in the glacial history of this region by targeting the previously undated Late Pleistocene record. Late Pleistocene glaciers were restricted to the cirques and upper valleys of Mount Tymphi. Terminal and lateral moraines between 1700 m and 2050 m a.s.l. mark the extent of Late Pleistocene glaciers on the southern side of Mount Tymphi. Moraines marking the maximum extent of Late Pleistocene glaciation date to 29.0 ± 3.0 ka and 25.7 ± 2.6 ka, taking the oldest ages as most representative of moraine emplacement. Glaciers had retreated to the high cirques by 24.5 ± 2.4 ka during Heinrich Stadial 2. Rock glaciers formed under cold and drier conditions during this period of glacier retreat. This 36Cl dataset complements published U-series ages from secondary calcites in glacial sediments below 1700 m elevation, which demonstrate more extensive Middle Pleistocene glaciations in MIS 6 and MIS 12. A Late Pleistocene glacier maxima on Mount Tymphi at 25.7–29 ka is in good agreement with well-preserved outwash sediments dating to 24–28 ka in the Voidomatis River record downstream and is consistent with the Ioaninna basin pollen record indicating cool and wet conditions, most favourable for glacier growth, at 25–30 ka. Crown Copyright © 2020 Published by Elsevier Ltd.
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    Negative ionisation efficiencies for 10Be, 26Al and Pu with MCSNICS at ANSTO
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Wilcken, KM; Child, DP; Hotchkis, MAC; Mann, M; Simon, KJ; Koll, D; Wallner, A; Hauser, T; Kitchen, R
    Low overall detection efficiency for actinides and cosmogenic isotopes (Al, Be) is the limiting factor affecting precision and sensitivity for applications where the amount of available sample material is small and/or rare isotope concentration is low. Due to low ionisation efficiencies for these isotopes it is not uncommon that more than 99% of the rare isotopes in the sample do not contribute to the statistical precision of the measurement. Optimising ion transmission and detection efficiency in the AMS measurement offers some room for improvement but these avenues are already close to their theoretical limits. On the other hand, optimising the performance and operation of the negative ion Cs-sputter sources has significant scope for improvement but is challenging. One often needs to compromise between competing requirements, for example, maintaining high sputtering rate to allow expedient consumption of the sample material but at the same time keeping the source insulators clean for longevity. The lack of a well-understood theoretical model for the negative ionisation process adds to the engineering challenges. Negative ionisation efficiencies above 30% have been demonstrated for radiocarbon [1] but remain often more than an order of magnitude lower for Be, Al and actinides. This is sometimes taken to be an inherent limitation of the technique, rather than a challenge to be addressed. Here we present details of the modified MC-SNICS sources at ANSTO, including engineering modifications that have improved longevity and stability. With attention to a combination of ion source running conditions, sample masses and sample binders the total efficiency for Pu measurements was increased up to 1.5%, corresponding to a negative ionisation yield of 4%. For Aland BeO- negative ion source yields are 0.2% and 3%, respectively.
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    A new method for separation and purification of beryllium and aluminium
    (GNS Science, 2011-03-24) Child, DP; Simon, KJ
    The DIPEX® resin manufactured by Eichrom was originally developed for the separation and preconcentration of actinides from nuclear industry waste streams and digested environmental samples. The resin has in recent years been investigated for use in separation of beryllium from a wide range of other elements which interfere with the determination of beryllium by ICP-AES. Application of this resin to purification of beryllium from environmental samples for analysis by Accelerator Mass Spectrometry (AMS) may allow for simplified sample processing in a single step and reduced interferences. AMS measurements of the cosmogenic isotope 10Be however are susceptible to a different selection of interfering elements than those which affect ICP-AES measurements. 10Be measurements are most commonly performed on melted ice and purified quartz. Both these sample types are generally low in elemental impurities such as magnesium, calcium, aluminium, titanium and iron with concentrations typically no more than a few hundred ppm in purified quartz and only a few ppm in ice however potential interferences still exist that must be removed prior to analysis. Two of the most significant interfering elements are boron and titanium. The isobar 10B, if sufficiently abundant, interferes with 10Be measurements by increasing the measurement background. Titanium has a retarding effect on caesium sputter ionisation and so on ion source output. The DIPEX resin has been evaluated as a single column purification and separation method for preparation of samples for AMS analysis. In this paper we present data on this evaluation including: • Evaluation of the resin capacity and selectivity for aluminium in a simulated matrix representing digested quartz and melted ice • Evaluation of the selectivity of the resin for beryllium in a simulated matrix representing digested quartz and melted ice • Assessment of the resin’s capacity to separate interfering matrix elements from the beryllium fraction.Copyright (c) 2011 AMS12
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    A quasi-monthly record of 10Be concentration at Law Dome, Antarctica, from 2000 to 2015
    (Antarctic Climate and Ecosystems Cooperative Research Centre, 2016-03-07) Smith, AM; Curran, MAJ; Etheridge, DM; Galton-Fenzi, BK; Heikkilä, UE; Klekociuk, AR; Moy, AD; Pedro, JB; Simon, KJ; van Ommen, TD
    This paper presents an overview of work undertaken over a number of Australian Antarctic Science projects, beginning in season 2001/02 with a shallow snow pit. In season 2005/06 this was augmented with a 260 m thermally drilled ice core and a 4.5 m snow pit. A core taken in 2008/09 overlapped the 2005/06 core and pit samples. From 2009/10, short cores spanning a few year’s deposition, along with snow pit samples spanning about half a year, have been taken each season. This has continued through to the current 2015/16 season. The cores permit an overlap with earlier years to match the chronology and to yield samples for 10Be analysis at the Australian Nuclear Science and Technology Organisation (ANSTO) by the technique of accelerator mass spectrometry (AMS). Together, the data provide a unique, continuous, quasi-monthly record over 2000 to 2015 as we have moved from Solar Cycle 23 to 24. The snow pits yield larger samples for 7Be analysis, earlier by gamma spectroscopy but lately by AMS. Along with comparison with neutron monitor data and GCM modelling, this unique, high-precision record has enabled us to learn much about the production, transport and deposition of 10Be to Law Dome and to improve our use of 10Be as a proxy for past solar variability.