Browsing by Author "Sinclair, D"

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    Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements
    (John Wiley & Sons, Inc, 2013-07-25) Hathorne, EC; Gagnon, A; Felis, T; Adkins, J; Asami, R; Boer, W; Caillon, N; Case, D; Cobb, KM; Douville, E; deMenocal, P; Eisenhauer, A; Garbe-Schönberg, D; Geibert, W; Goldstein, S; Hughen, K; Inoue, M; Kawahata, H; Kölling, M; Cornec, FL; Linsley, BK; McGregor, HV; Montagna, P; Nurhati, IS; Quinn, TM; Raddatz, J; Rebaubier, H; Robinson, L; Sadekov, A; Sherrell, R; Sinclair, D; Tudhope, AW; Wei, GJ; Wong, HKY; Wu, HC; You, CF
    The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1. ©2013 American Geophysical Union
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    Towards the development of fire proxies in speleothems using geochemical signatures in ashes from bushfires
    (Australasian Quaternary Association Inc., 2022-12-06) Campbell, M; McDonough, LK; Naeher, S; Treble, PC; Grierson, P; Sinclair, D; Howard, DL; Baker, AA
    Our knowledge of past fire regimes is limited by short observational records. Proxy archives (such as sediment cores, ice cores, speleothems, and tree scars) are used to extend these records and develop a better understanding of past fire regimes. Recently, stalagmites (i.e., cave deposits), have been shown to record past fire events, and it is possible that they include other attributes of the fire regime (e.g. burn severity). Stalagmite fire proxies are both chemical (e.g. oxygen isotope composition of calcite, and nutrient and trace metal concentrations), and physical (e.g. growth rate, fabric). Trace metals and nutrients are leached from ash and subsequently transported to the stalagmite via hydrological pathways. We collected ash from four Australian karst sites which experienced fires in recent years (2019 and 2022). Ash chemical composition was determined by analysis of leachates (inorganic chemistry) and by analysis of the ash itself (organic biomarker concentrations of a subset of the ash dataset). The concentrations of inorganic components (e.g. of trace metals strontium and magnesium) show a clear difference between more- and less-combusted materials, as inferred by ash colour. Common fire biomarker concentrations (e.g. polycyclic aromatic hydrocarbons and levoglucosan) showed no clear relationship with inferred burn severity. Together, this has implications for the use of both organic and inorganic fire proxies in stalagmites and other sedimentary proxy archives. Inorganic ash geochemistry results will be used to contextualise changes in stalagmite geochemistry from Western Australian stalagmites (as measured by LA-ICP-MS and Synchrotron micro-XFM) which experienced bushfires during the satellite era. We aim to determine whether stalagmite chemistry can be used as a proxy for burn severity.
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    Towards the development of fire proxies in speleothems using geochemical signatures in ashes from bushfires
    (Australasian Quaternary Association Inc., 2022-12-06) Campbell, M; McDonough, LK; Naeher, S; Treble, PC; Grierson, P; Sinclair, D; Howard, DL; Baker, AA
    Our knowledge of past fire regimes is limited by short observational records. Proxy archives (such as sediment cores, ice cores, speleothems, and tree scars) are used to extend these records and develop a better understanding of past fire regimes. Recently, stalagmites (i.e., cave deposits), have been shown to record past fire events, and it is possible that they include other attributes of the fire regime (e.g. burn severity). Stalagmite fire proxies are both chemical (e.g. oxygen isotope composition of calcite, and nutrient and trace metal concentrations), and physical (e.g. growth rate, fabric). Trace metals and nutrients are leached from ash and subsequently transported to the stalagmite via hydrological pathways. We collected ash from four Australian karst sites which experienced fires in recent years (2019 and 2022). Ash chemical composition was determined by analysis of leachates (inorganic chemistry) and by analysis of the ash itself (organic biomarker concentrations of a subset of the ash dataset). The concentrations of inorganic components (e.g. of trace metals strontium and magnesium) show a clear difference between more- and less-combusted materials, as inferred by ash colour. Common fire biomarker concentrations (e.g. polycyclic aromatic hydrocarbons and levoglucosan) showed no clear relationship with inferred burn severity. Together, this has implications for the use of both organic and inorganic fire proxies in stalagmites and other sedimentary proxy archives. Inorganic ash geochemistry results will be used to contextualise changes in stalagmite geochemistry from Western Australian stalagmites (as measured by LA-ICP-MS and Synchrotron micro-XFM) which experienced bushfires during the satellite era. We aim to determine whether stalagmite chemistry can be used as a proxy for burn severity.