ANSTO :: Browsing by Author "Bird, MI"

Browsing by Author "Bird, MI"

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The climate reconstruction potential of Acacia cambagei (gidgee) for semi-arid regions of Australia using stable isotopes and elemental abundances
(Elsevier B.V., 2017-01-01) Witt, GB; English, NB; Balanzategui, D; Hua, Q; Gadd, PS; Heijnis, H; Bird, MI
To provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of Australia it is necessary to investigate the potential climate signals in tree species in this large region. Using a stable isotope and x-ray fluorescence approach to dendrochronology in Acacia cambagei, this study demonstrates short (10 years) proxies of temperature and precipitation are possible. Because rings in A. cambagei are difficult to see, precluding traditional dendrochronology, we used elemental abundances of Ca and Sr as an annual chronometer back to 1962. Radiocarbon analysis confirmed that our dating of wood from two trees. We compared δ13C and δ18O from the α-cellulose of the dated wood over the most recent 10 years (n = 10) to local climate records demonstrating significant relationships between δ18O and precipitation (r = −0.85, p < 0.002); mean monthly maximum temperature (r = 0.69, p < 0.03); and drought indexes (CRU scPDSI 0.5°, r = −0.89, p < 0.001) for February and March. Acacia cambagei may be useful in developing regional networks of climate proxies for drought. Using modern trees, in combination with architectural timbers, it may be possible to construct a multi-century, annually-resolved proxy-record of rainfall and temperature for semi-arid north-eastern Australia. © 2016 Elsevier Ltd.
The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments – ABOX, ABA and hypy
(Elsevier, 2014-08-01) Bird, MI; Levchenko, VA; Ascough, PL; Meredith, W; Wurster, CM; Williams, AG; Tilston, EL; Snape, CE; Apperley, DC
Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ∼1 pMC after one year (apparent age of ∼40,000 yrs BP) and ∼5 pMC after three years (apparent age of ∼25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ∼350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique.© 2014, Elsevier B.V.
Extreme seasonal shifts in water and carbon sources to a wet-dry tropical river
(Copernicus Publications, 2019-04-07) Duvert, C; Hutley, LB; Birkel, C; Rudge, M; Munksgaard, NC; Wynn, JG; Setterfield, SA; Cendón, DI; Bird, MI
In regions with extreme climatic seasonality, the riverine export of carbon is expected to be driven by changes in connectivity between source areas and rivers. Yet we lack a thorough understanding of the relative contributions of each water source (e.g. wetlands, shallow soils, deep aquifers) to the dissolved carbon flux, and of the way these contributions vary with seasonal changes in flow regime. Here we assess the temporal variations in dissolved inorganic carbon (DIC) fluxes in a wet-dry tropical river of northern Australia, using weekly to monthly measurements of electrical conductivity, DIC and its carbon isotopic ratio ( 13CDIC), as well as the isotopes of water ( D, 18O and 3H), over a two-year period. We use linear mixing models integrated into a Bayesian framework to determine the relative contributions of stormflow, saturation areas, shallow groundwater and a deep carbonate aquifer to river fluxes, which we relate to water ages using lumped models fitted to isotopic time-series. Our results suggest extreme shifts in water and associated carbon sources between the wet and dry seasons. During the wet season, most DIC was transported by young water sources (< 1 year) originating mainly from saturation areas (52–82%) and stormflow (13–40%). This DIC was of biogenic origin (mean 13CDIC –18h). As rainfall ceased, the drainage of floodplains and wetlands occurred until all saturation areas either dried out or became disconnected from the river network. From this stage, river flow decreased substantially and the remaining DIC was nearly entirely conveyed via deeper, older water sources (20–40 years) from the underlying carbonate formation (85–95%). This DIC had a likely geogenic origin (mean 13CDIC –14h). Because of the disproportionately high flows during the wet season, the flux of DIC was larger during that period, an indication of the prevalence of biogenic carbon to the total DIC flux in this system. Our findings illustrate the need to consider dominant water flowpaths, as well as their changing patterns of connectivity, if we are to inform carbon fluxes across catchments. This work also suggests that carbon inputs to rivers need to be systematically partitioned between biogenic and geogenic sources, as this is an important consideration when evaluating the strength of soil carbon sinks. © Author(s) 2019. CC Attribution 4.0 license.
Fire and fuel in Holocene northern Australian tropical savannas
(International Union for Quaternary Research (INQUA), 2019-07-26) Rehn, E; Bird, MI; Rowe, C; Ulm, S; Woodward, C; Jacobsen, GE
Fire has a long history of interaction with Australian ecosystems but poses a growing risk as future climate change is predicted to lengthen fire seasons and increase extreme fire weather. Tropical savannas cover almost one quarter (1.9 million km2) of the Australian land mass, and fire occurs here almost annually. A greater understanding of past fire regimes, and their environmental context, is essential for management and planning in an increasingly fire-prone landscape. Despite the central importance of fire in savanna ecosystems, the region remains understudied in Australian palaeofire research. In light of this knowledge gap, this study combines established and emerging optical and chemical methods for charcoal analysis in the context of northern Australian tropical savannas. This study presents three new Holocene palaeofire records from tropical savanna wetland sites in far northern Australia, each with diverse land-use histories. Three methods were applied to achieve a more comprehensive understanding of fire and fuels over time in tropical savannas. Charcoal abundance is presented for four size classes covering a local signal (>250 µm and 250-125 µm) and surrounding regional signal (125-63 µm and <63 µm). Particle morphology and aspect ratio are proposed indicators of fuel type (e.g. grass, leaf, wood). However, this technique derives primarily from temperate environments, notably from experimental burns and sites in the Northern Hemisphere. Our study tests methods developed in temperate, Northern Hemisphere settings on charcoal from the Australian tropical savanna. Fuel type data are discussed using a morphotype classification system, and a length-width ratio of ≥3.6 is used to identify macroscopic grass particles. We demonstrate the application of chemical quantification of pyrogenic carbon (PyC) as well as isotopic identification of fuel type. PyC abundance determined using hydrogen pyrolysis and δ13C composition (contribution of C3 versus C4 plants) are presented for the three sites and combined with the data generated using optical methods. All records are supported by 210Pb and 14C chronologies and XRF core scanner data on elemental composition. Preliminary results show negligible variations in fuel composition through time at each site, with broad correspondence between fuel type determined by morphology and isotope composition. Variations are apparent between different charcoal size classes (macroscopic and microscopic) in both abundance and fuel composition at all sites, reflecting differences in local and regional fire signals and highlighting the importance of size differentiation during analysis. This study is a step towards filling the palaeofire knowledge gap represented by northern Australia and is an important assessment of the application of existing palaeofire techniques to this unique context. © The Authors.
Improved pretreatment method for the isolation and decontamination of pyrogenic carbon for radiocarbon dating using hydrogen pyrolysis
(Elsevier, 2021-02-01) Orr, TJ; Wurster, CM; Levchenko, VA; Ascough, PL; Bird, MI
Pyrogenic carbon (charcoal, black carbon, elemental carbon) is one of the most common materials used for radiocarbon dating of terrestrial samples. However, exogenous carbon contamination can compromise the accuracy of radiocarbon ages. This study presents the results of two chemical pretreatments prior to hydrogen pyrolysis (hypy) as improved protocols for the isolation and decontamination of pyrogenic carbon, i) a simple acid-oxidation step (A-Ox/hypy) and ii) acid-base-acid (ABA/hypy). The A-Ox/hypy protocol uses HNO3 and H2O2, while ABA/hypy uses HCl and NaOH. Both pretreatments remove labile and inorganic carbon before hypy, decreasing the potential for in situ production of pyrogenic carbon during the hypy reaction. The effectiveness of each protocol was directly measured on charcoal artificially produced at 350 °C, 450 °C and 550 °C from radiocarbon-free wood, and exposed to environmental contamination for 1–3 yrs. The results show a >94% reduction in carbon contamination for the 450 °C and 550 °C charcoal samples occurred using A-Ox/hypy, but this treatment was less effective for the 350 °C charcoal. A >99% reduction in carbon contamination in all charcoal samples examined occurred using ABA/hypy. The A-Ox/hypy protocol was further tested on cave guano sediments, which had previously reported erroneous dates following simple organic solvent extraction followed by ABA pretreatment. Effective decontamination was achieved using A-Ox/hypy on the guano, which corrected a radiocarbon age reversal. Overall, ABA/hypy effectively decontaminated the charcoals and was a more efficient pretreatment for charcoal than A-Ox/hypy, however resulting in larger sample mass loss. Therefore, ABA/hypy is the recommended protocol for older (>30,000 14C yr BP) charcoal or sediment samples, or where date accuracy is imperative, while A-Ox/hypy represents an improved protocol for the quick and cost-effective measurement of younger samples (<30,000 14C yr BP) when sample size is of concern. © 2021 Elsevier B.V.
The influence of C3 and C4 vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems
(European Geosciences Union, 2015-08-26) Saiz, G; Bird, MI; Wurster, CM; Quesada, CA; Ascough, PL; Domingues, T; Schrodt, F; Schwarz, M; Feldpausch, TR; Veenendaal, E; Djabeletey, G; Jacobsen, GE; Hien, F; Compaore, H; Diallo, A; Lloyd, J
Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C=N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk 13C and sand content explaining 0.63 of the observed variability. The variation of 13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend also being strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise the confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times ( ) even in deep soil layers, while the most stable SOM fraction associated with silt and clay exhibited shorter in the savanna woodland than in the neighbouring forest stand. These results, together with the vertical variation observed in 13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations.However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. Thisstudy shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM. © 2015, Copernicus Publications.
Loss and gain of carbon during char degradation
(Elsevier, 2017-03-01) Bird, MI; McBeath, AV; Ascough, PL; Levchenko, VA; Wurster, CM; Munksgaard, NC; Smernik, RJ; Williams, AA
We report results of a study examining controls on the degradation of chars produced at 300, 400 and 500 °C from radiocarbon-free wood, deployed for three years in a humid tropical rainforest soil in north Queensland, Australia. The chars were subjected to four treatments (i) no litter (ii) covered by leaf litter, (iii) covered by limestone chips to alter local pH, and (iv) covered by limestone chips mixed with leaf litter. Radiocarbon, stable isotope and proximate analyses indicate significant ingress of exogenous (environmental) carbon and mineral material, strongly correlated with loss of indigenous (char) carbon from the samples. While indigenous carbon losses over three years were generally <8% for the char produced at 500 °C char under any treatment, chars formed at lower temperatures lost 5–22% of indigenous carbon accompanied by ingress of up to 7.5% modern exogenous carbon. The data provide clear evidence of a direct link between the ingress of exogenous carbon, likely at least partly due to microbial colonization, and the extent of char decomposition. Failure to account for the ingress of exogenous carbon will lead to a significant under-estimate of the rate of char degradation. © 2016, Elsevier Ltd.
Molecular complexity and diversity of persistent soil organic matter
(Elseiver B. V., 2023-09) Jones, AR; Dalal, RC; Gupta, VVSR; Schmidt, S; Allen, DE; Jacobsen, GE; Bird, MI; Grandy, AS; Sanderman, J
Managing and increasing organic matter in soil requires greater understanding of the mechanisms driving its persistence through resistance to microbial decomposition. Conflicting evidence exists for whether persistent soil organic matter (SOM) is molecularly complex and diverse. As such, this study used a novel application of graph networks with pyrolysis-gas chromatography-mass spectrometry to quantify the complexity and diversity of persistent SOM, defined as SOM that persists through time (soil radiocarbon age) and soil depth. We analyzed soils from the Cooloola giant podzol chronosequence across a large gradient of soil depths (0–15 m) and SOM radiocarbon ages (modern to 19,000 years BP). We found that the most persistent SOM on this gradient was highly aromatic and had the lowest molecular complexity and diversity. By contrast, fresh surface SOM had higher molecular complexity and diversity, with high contributions of plant-derived lignins and polysaccharides. These findings indicate that persisting SOM declines in molecular complexity and diversity over geological timescales and soil depths, with aromatic SOM compounds persisting longer with mineral association. © 2023 Elsevier Ltd
A radiocarbon chronology for Sanamere Lagoon, Cape York Peninsula, using multiple organic fractions
(Elsevier B. V., 2022-05) Rivera-Araya, M; Rowe, C; Levchenko, VA; Ulm, S; Bird, MI
The selection and pre-treatment of reliable organic fractions for radiocarbon age determination is fundamental to the development of accurate chronologies. Sampling from tropical lakes is particularly challenging given the adverse preservation conditions and diagenesis in these environments. Our research is the first to examine and quantify the differences between radiocarbon ages from different carbon fractions and pretreatment protocols from tropical lake sediments. Six different organic fractions (bulk organics, pollen concentrate, cellulose, stable polycyclic aromatic carbon (SPAC), macrocharcoal >250 μm and microcharcoal >63 μm) were compared at six different depths along a 1.72 m long core extracted from Sanamere Lagoon, Cape York Peninsula, northern Australia. Acid-base-acid (ABA), modified ABA (30% hydrogen peroxide + ABA), 2chlorOx (a novel cellulose pre-treatment method) and hydrogen pyrolysis (hypy) were used to pre-treat the organic fractions. The oldest date is ∼31,300 calibrated years before present (cal yr BP) and the youngest is ∼2800 cal yr BP, spanning ∼28,500 years. The smallest offset between the minimum and the maximum age for different fractions and across pretreatment methods at a given depth was found to be 832 years (between SPAC and pollen) and the largest ∼16,750 years (between pollen concentrate and SPAC). The SPAC fractions pre-treated with hypy yielded older ages compared to all other fractions in most cases, while bulk organics yielded consistently younger ages. The magnitude and consistency of the offsets and the physical and chemical properties of the tested organic fractions suggest that SPAC is the most reliable fraction to date in tropical lake sediments and that hypy successfully removes exogenous carbon contamination. © 2022 Elsevier B.V.
Seasonal shift from biogenic to geogenic fluvial carbon caused by changing water sources in the wet-dry tropics
(American Geophysical Union, 2020-02-05) Duvert, C; Hutley, LB; Birkel, C; Rudge, M; Munksgaard, NC; Wynn, JG; Setterfield, SA; Cendón, DI; Bird, MI
The riverine export of carbon is expected to be driven by changes in connectivity between source areas and streams. Yet we lack a thorough understanding of the relative contributions of different water sources to the dissolved carbon flux, and of the way these contributions vary with seasonal changes in flow connectivity. Here we assess the temporal variations in water and associated dissolved inorganic carbon (DIC) sources and fluxes in a wet-dry tropical river of northern Australia over two years. We use linear mixing models integrated into a Bayesian framework to determine the relative contributions of rainfall, seasonal wetlands, shallow groundwater, and a deep carbonate aquifer to riverine DIC fluxes, which we relate to the age of water sources. Our results suggest extreme shifts in water and DIC sources between the wet and dry seasons. Under wet conditions, most DIC was of biogenic origin and transported by relatively young water sources originating from shallow groundwater and wetlands. As rainfall ceased, the wetlands either dried out or became disconnected from the stream network. From this stage, DIC switched to a geogenic origin, nearly entirely conveyed via older water sources from the carbonate formation. Our findings demonstrate the importance of changing patterns of connectivity when evaluating riverine DIC export from catchments. This work also illustrates the need to systematically partition DIC fluxes between biogenic and geogenic sources, if we are to quantify how the riverine export of carbon affects net carbon soil storage. © 2021 American Geophysical Union

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