APO Collection: ANSTO authored conference publications

Variations in marine reservoir corrections for the Great Barrier Reef during the last 7000 years

2011-03-20T13:00:00Z

Title: Variations in marine reservoir corrections for the Great Barrier Reef during the last 7000 years Authors: Hua, Q; Webb, G; Zhao, J.; Nothdurft, L; Price, G Abstract: For calibration of marine 14C ages, marine reservoir correction value (ΔR) of a given location is generally assumed to be constant with time. However, variations in the marine reservoir effect of several hundred to a couple of thousand years have been observed for various regions in the Pacific, Atlantic and Mediterranean during the Late-glacial and Holocene. These variations result from changes in ocean circulation and the carbon cycle associated with climate change. Here we present a new data set of ΔR for the Great Barrier Reef (GBR) in south-western Pacific Ocean during the last 7000 years for the investigation of possible variability in the marine reservoir effect of this area and for improving radiocarbon dating of marine samples. Coral samples used in this study were from shallow cores and storm derived blocks collected on Heron Reef in southern GBR at 23º26'S, 151º55'E. Fifteen unaltered coral samples (based on SEM screening, δ234U and initial 230Th/232Th ratios) were analysed for 230Th/U and 14C. 230Th dates were determined by TIMS Useries in the Radiogenic Isotope Laboratory at the University of Queensland with a precision better than 0.5% (2σ). Aliquots of these dated corals were then taken for radiocarbon analysis. The samples were cut by diamond saw, cleaned in deionised water, oven dried, and homogenised in a mortar and pestle prior to 14C analysis using the STAR AMS facility at ANSTO. A typical precision for 14C analysis is <0.4% (1σ). The results of this investigation will be compared with those of previous studies for the Pacific, and variations in ΔR for the GBR for the mid- to late Holocene and their possible mechanisms will be then discussed. This work was supported by AINSE grant 09/056. Copyright (c) 2011 AMS12.

A cold finger cooling system for the efficient graphitisation of microgramsized

2011-03-23T13:00:00Z

Title: A cold finger cooling system for the efficient graphitisation of microgramsized Authors: Yang, B; Smith, A; Hua, Q Abstract: At ANSTO we use the Bosch reaction to convert sample CO2 to graphite for production of our radiocarbon AMS targets. Key to the efficient graphitisation of ultra-small samples is the type of iron catalyst and the effective trapping of water vapour in a ‘cold finger’ during the reaction. We have developed a simple liquid nitrogen cooling system that enables us to rapidly adjust the cold finger temperature in our laser-heated ‘microfurnace’, optimised for the graphitisation of microgram-sized carbon samples. This system is used to firstly transfer the CO2 into the microfurnace, to maintain the cold finger at -80°C for ~ 5 minutes while the CO2 is converted to CO and then at -160°C for ~ 25 minutes for the remainder of the reaction as the CO is converted to graphite. It comprises a machined aluminium cylinder mounted in the insulated cap of a 600 ml Dewar. The lower end is submerged in liquid nitrogen (LN2). The upper end has a smaller diameter which is wound with an electric heating element and is provided with a thermocouple and a central hole into which the cold finger is inserted. Electrical power to the heater is adjusted by PID control, permitting the cold finger temperature to be adjusted over the range -50°C to -160°C at rates of up to 40°C/min. This simple system uses modest amounts of LN2 (typically < 0.2 L/hr during graphitisation) and is compact and reliable. We have used it to produce over 120 AMS targets containing between 5 and 20 μg of carbon, with conversion efficiencies for 5 μg targets of typically 90-100%. We are currently modifying this cooling system for use with our conventional graphitisation reactors. Copyright (c) 2011 AMS12

Early results from the ANSTO/NIWA 14C of atmospheric methane program

2011-03-23T13:00:00Z

Title: Early results from the ANSTO/NIWA 14C of atmospheric methane program Authors: Smith, A; Brailsford, G; Yang, B; Bromley, T; Martin, R Abstract: development and proving of the laser heated microfurnace we have used it to prepare 45 samples of ~ 16 μg of carbon. These comprised CO2, derived from atmospheric methane, frozen back into glass breakseals following measurement for δ13C at NIWA. There were three sample sets: 15 from Baring Head, NZ (BHD), collected each ~ 15 days between March and September 2009, 9 from Arrival Heights, Antarctica (SCT), collected each ~ 41 days between February 2008 and January 2009, plus 21 samples taken along a Pacific Ocean voyage from Nelson (NZ) – Osaka (Japan) in December 2005 (FTW). All samples were measured to better than 1% precision, sufficient to reveal a 14CH4 signal. The BHD set shows significant temporal variation in 14C for baseline air passing over the Southern Ocean, whereas the SCT set shows a lesser variation for Antarctic air. The FTW set covers a S-N transect across the Pacific Ocean, showing the influence of the ITCZ (5°-10° N) and different meteorological conditions on the concentration, δ13C and Δ14C of CH4 and demonstrates that CH4 is not well mixed. Graphitisation reactions averaged 32 min with 0.7 mg of Fe, reduced from Fe2O3, as the catalyst. The samples, blanks and standards were measured in two 10 minute blocks; some were measured again to improve statistics. Average 13C4+ currents per microgram of carbon were 13, 4 and 2 nA/μg for each 10 min block. Similarly-sized targets prepared in the conventional furnace with Fe2O3 gave 8, 5 and 2 nA/μg for each 10 min block. Graphitisation efficiencies were typically 90- 100% for microfurnace samples, compared with 37-84% for conventional furnace samples. Subsequent examination by microscope showed that the cesium beam was well-centred on the 1 mm diameter recess and that effectively all C/Fe was sputtered, leading to a (minimum) estimation of ~4% overall AMS measurement efficiency. Copyright (c) 2011 AMS12

Mid-Late Quaternary vegetation and climate change reconstructed from palynology of marine cores off southwestern New Zealand

2011-07-20T14:00:00Z

Title: Mid-Late Quaternary vegetation and climate change reconstructed from palynology of marine cores off southwestern New Zealand Authors: Ryan, M; Newnham, RM; Dunbar, G; Vandergoes, M; Neil, H; Bostock, H Abstract: This paper presents preliminary findings from a new PhD investigation that aims to produce a long continuous mid-late Quaternary record of terrestrial pollen, vegetation, and climate. Records are generated from marine cores collected ca. 100 km west of the central South Island of New Zealand (ca. 42 oS, 170 oE). These cores were collected as part of the 2006 MATACORE voyage of R/V Marion DuFresne. Core sites were located on channel levees that have aggraded with sea-level rise, and are fed by river discharge and littoral drift where they cross the shelf and upper slope. The main core to be used in this study extends from the present back to Marine Isotope Stage (MIS) 11, on the basis of preliminary ?18O stratigraphy, at an estimated sedimentation rate of 10 cm ka-1, which is comparatively high for the NZ region. Previous investigation of similar marine sequences has revealed their unexpected capacity for generating robust pollen records that mirror those produced at adjacent sites on land. This, allied with analysis of surface samples, has indicated the likely provenance and vegetation source area of the pollen. The marine sequences provide additional benefits to their terrestrial counterparts, notably the capacity to generate long, continuous pollen records with rigorous chronologies. These chronologies can be intimately tied to other marine proxies, investigated in the same sequences, and the climate reconstructions generated from them. These terrestrially influenced, high sedimentation, West Coast cores will enable stronger insights than were previously possible into marine and terrestrial climate in the southern mid-latitudes across the last 4-5 glacial-interglacial cycles. Of particular interest are the differences in timing of response to climate transitions, between the marine and terrestrial realms and between the southern mid-latitudes and northern hemisphere and Antarctic glaciations. Copyright (c) 2011 INQUA 18