Browsing by Author "Opdyke, BN"

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    Beryllium-10 in forams and marine sediments; a new chemo-stratigraphic tracer for the late quaternary
    (Eleventh International Conference on Accelerator Mass Spectrometry, 2008-09) Levchenko, VA; Opdyke, BN; Fink, D; Mifsud, C; Williams, AA
    The production rate of cosmogenic isotopes 10Be and 14C is influenced by varitions in the primary cosmic ray flux and by charges of the Earth's magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Lashamp Mono Lake excursion, circa 41 ka BP). Understanding these changes and synchronising variations in palaeomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly in the interval between 20 and 50 ka ago, and establish reliable chronologies for ocean sedimentation rate changes. A common proxy for these palaeomagnetic changes is atmospheric fallout of 10Be in bulk sediments. However terrigenous and recycled sediments also deliver high 10Be concentrations thus strongly complicating the process required to isolate direct atmospheric from continental derived 10Be. As an alternative to geochemical speciation, grain size or leaching procedures in sediments we suggest that changes in 10Be concentrations in planktonic foraminifera can be used as a global stratigraphic marker. We are investigating planktonic foraminifera collected from Core MD - 982167, which was recovered from the Scott Plateau in the Eastern Indian Ocean at latitude of 13° S. The MD- 982167 already has an established stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm per ka. Initial results of paired 14C and 10Be determinations in foraminifera and fine fraction of the core sediments as a function of core depth have been obtained and subsequently will be compared to palaeomagnetic measurements currently in progress. An improved chronology for this high resolution core that has recorded brief, less than one thousand year duration, climatic events during the studied time interval will allow much better correlation between marine sedimentary records and the detailed chronologies established from the ice cores.
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    Identifying groundwater-surface water interactions and groundwater geochemistry in the Upper Murrumbidgee Catchment using surface water surveys
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Gray, SS; Moore, CL; Opdyke, BN; Hughes, CE
    Evidence suggests that potable groundwater occurs within the fractured crystalline rock of the Upper Murrumbidgee catchment, with anecdotal reports that bore yields and fracture networks could form aquifers capable of sustaining regional population growth and agricultural development. However, little knowledge relating to groundwater flow or recharge and discharge mechanisms exists. Hydrogeochemical methods are particularly useful in studying groundwater in complex geological environments. Unfortunately, limited information regarding groundwater geochemistry exists in this catchment. Surface water surveys provide an opportunity to quickly obtain preliminary information regarding groundwater-surface water interactions and likely groundwater geochemistry. Four surface water surveys were conducted at up to 285 sites during wet and dry conditions from September 2017 to April 2019. Physicochemical parameters were collected at each site where water was present, along with samples for stable isotopes (δ18O and δ2H) and dissolved ion analysis. Surface water geochemistry is influenced by interactions between altitude, rainfall, and outcropping geology. Stream electrical conductivity (EC) is positively correlated with altitude and negatively correlated with rainfall in all sub-catchments except the Yass River catchment. Outcrop geology also influenced stream EC, with the EC lowest over Paleozoic granite and granodiorites; moderate over Paleozoic felsic volcanic, Cenozoic mafic volcanic, and Cenozoic alluviums; and highest over Ordovician metasediments. Dissolved ion chemistry is similarly influenced by outcrop geology, and is reflected in preliminary groundwater surveys. The cations Na+ and K+ dominate Paleozoic granite and granodiorite waters while Ca2+ and Mg2+ dominate Cenozoic mafic volcanic waters. Bicarbonate (as HCO3-) is the dominant anion, with elevated HCO3-/Cl- associated with Cenozoic mafic volcanics. This suggests that mineral weathering dominates hydrogeochemical processes. Spatial distributions of stream water δ18O and δ2H highlight potential baseflow areas. Results suggest that potable water is highly probable within Paleozoic granite and granodiorites, with water Na+-K+-HCO3- dominated. Potable water is possible within Paleozoic felsic volcanic, Cenozoic mafic volcanic, and Cenozoic alluviums, with water potentially more suitable for agricultural use due to the higher Ca2+, Mg2+, and HCO3- content. Ordovician metasediment water is more suitable for agricultural use. Surface water survey data will be used in this study to optimise groundwater survey design and develop improved conceptual models to describe groundwater flow and recharge and discharge mechanisms in fractured rock environments in the Upper Murrumbidgee catchment. This will increase our understanding on how water resources may be utilised to support regional population growth and agricultural development, providing future water security for the region. © The Authors
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    An improved radiocarbon chronology and calibration over the Laschamp event: 14C – 10Be cross synchronisation
    (Geological Society of Australia, 2010-07-04) Levchenko, VA; Opdyke, BN; Fink, D; Mifsud, C; Williams, AG; Klootwijk, C
    The production rate of cosmogenic isotopes 10Be and 14C is influenced by variations in the primary cosmic ray flux and by changes of the Earth’s magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Lashamp/Mono Lake excursion, circa 41 ka BP). Understanding these changes and synchronising variations in palaeomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly in the interval between 20 and 50 ka ago, and establish reliable chronologies for ocean sedimentation rate changes. A common often used proxy for these palaeomagnetic changes is atmospheric fallout of 10Be in marine sediments. We are investigating the Core MD – 982167, which was recovered from the Scott Plateau in the Eastern Indian Ocean at latitude of 13°S. The MD‐982167 already has an established stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm per ka. A series of 14C and 10Be determinations in foramifera and fine fraction of the core sediments as a function of core depth have been obtained. Palaeomagnetic measurements with the aim to determine the position of geomagnetic disturbances like Laschamp and Mono Lake as recorded in the ocean sediments were also done on the samples from the same core. Synchronisation of palaeomagnetic, 10Be and radiocarbon records together with the application of 10Be pulse as a global chronostratigrafic marker is discussed. An improved chronology for this high resolution core that has recorded brief, less than one thousand year duration, climatic events during the studied time interval will allow much better correlation between marine sedimentary records and the detailed chronologies established from the ice cores.
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    An improved radiocarbon chronology for MD-982167, eastern Indian Ocean: synchronizing paleomagnetic intensity and 10Be across the Laschamp event
    (20th International Radiocarbon Conference, 2009-06-02) Levchenko, VA; Fink, D; Opdyke, BN; Mifsud, C; Williams, AG; Klootwijk, C
    The production rate of cosmogenic isotopes 10Be and 14C is influenced by variations in the primary cosmic-ray flux and by changes of the Earth’s magnetic field, which has experienced a number of significant perturbations during the late Quaternary (e.g. Laschamp excursion, ca. 41 kyr BP). Understanding these changes and synchronizing variations in paleomagnetic intensity derived from various marine sediment cores can often help constrain the quality of 14C dating, particularly for times beyond IntCal04 between 30 and 50 kyr ago, leading to improved overall core chronologies and determination of ocean sedimentation rates. An often used proxy for these paleomagnetic changes is the concentration of atmospheric fallout of 10Be in marine sediments. The ocean core MD-982167 recovered from the Scott Plateau in the eastern Indian Ocean (13°09′S, 121°35′E; depth of 1981m) has an established δ18O stable isotope stratigraphy and a high sedimentation rate of 10 to 20 cm/kyr based on a preliminary chronology tied to ice-core records. This in turn makes MD-982167 amenable to high-resolution 10Be assay across the Laschamp period. We have completed measurements of 10Be and 14C (in both foraminifera and fine sediments) and paleomagnetic intensity in core MD-982167. We are able to correlate variations in 10Be with paleomagnetic intensity recorded in these ocean sediments based on our detailed radiocarbon age-depth profile and confirm a strong presence of the Laschamp excursion at 39.9 ± 1.3 kyr BP. Comparing the variations of atmospheric-derived 10Be in MD-982167 tied to our improved radiocarbon chronology with 10Be established from the ice cores and will allow much better correlation between marine sedimentary and ice-core records across recent stadial and interstadial climatic events.
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    Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes
    (Elsevier, 2015-04-21) Hua, Q; Webb, GE; Zhao, JX; Nothdurft, LD; Lybolt, M; Price, GJ; Opdyke, BN
    Accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction Δ(R) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔR for the last ∼5.4 ka agree well with their modern value, but large ΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4–8 ka. The latter time interval also has significant variations with similar features in previously published Δ values for other sites in the Pacific, including southern Peru–northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔR values, instead of constant (modern) values, for age calibration of Holocene marine samples not only for the SW Pacific sites but also for other tropical and subtropical sites in the Pacific. Crown Copyright ©2015
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    Spatial and temporal stable isotope variability within Alpine Streams of the Snowy Mountains
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Parige, R; Gray, SS; Hughes, CE; Opdyke, BN; Moore, CL
    As an alpine region, the Snowy Mountains are identified as susceptible to the impacts of climate change. This is projected to influence annual variability in rainfall and snowfall amounts which will change availability of runoff water. The Snowy Mountains Hydro-electric Scheme has also altered natural flows in the area since the 1970s, changing behaviours of water resources in the Murrumbidgee and Snowy River catchments. Understanding processes that affect and have affected these surface waters can therefore improve the scientific basis for future water resource management decisions of the region. Historical physiochemical data of streams in the Snowy Mountains region has been monitored by NSW government and Snowy Hydro over the past half century. However, little stable water isotope data in alpine streams and rivers currently exists. As stable water isotopes (δ2H and δ18O) are excellent tracers of water through the hydrologic cycle, their use can better current understanding of the regions surface waters. Rapid stream surveys in 2019 have collected stable isotope and physiochemical data of streams within the Snowy Mountains, as well as Murray and Murrumbidgee systems downstream. Analyses of both these and archived samples from 2004-2017 were undertaken for this project. The data was then used with precipitation isotope data from parallel ANSTO studies, and historical records on regional streams for interpretation. Results showed that stable isotopes in streams varied spatially amongst sites with elevation, temperature difference, and location in the reservoir network, with distinct variance over smaller distances with steeper elevation. Temporal affects were seen with the appearance of seasonal snowmelt contributions into streams and climate. Physiochemical data saw trends similar to historical reports, with significant climate and geographic influence. This data will specifically contribute to further research into groundwater sustainability, isotope forensics and agricultural water use led by ANSTO and ANU for future betterment of the catchment. © The Authors