Browsing by Author "Goodwin, MJ"

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    Hydroclimate proxies for eastern Australia using stable isotopes in grey mangroves (Avicennia marina)
    (Elsevier, 2022-01) Goodwin, MJ; Verdon-Kidd, DC; Hua, Q; English, NB; Haines, HA; Allen, KJ
    The development of high-resolution terrestrial palaeoclimate records in Australia is hindered by the scarcity of tree species suitable for conventional dendrochronology. However, novel analytical techniques have made it possible to obtain climate information from tree species that do not reliably form annual growth rings. In this paper we assess the potential of stable carbon and oxygen isotopes in the xylem wood of grey mangroves (Avicennia marina (Forssk.) Vierh.) as hydroclimate proxies for eastern Australia. Bomb-pulse radiocarbon dating and simple age models were used to estimate the age of the growth layers in radial sequence in stems from four grey mangrove trees in two adjacent estuaries in New South Wales, Australia. Stable isotope data measured from the xylem wood of the four stems were composited to yield mean δ18O and δ13C series for the 1962–2016 period. Significant negative Spearman correlations were found between δ18O and rainfall, sea level, instrumental Palmer Drought Severity Index (scPDSI) and the El Niño Southern Oscillation (ENSO), while δ13C was positively correlated with temperature, vapour pressure and evapotranspiration. The results demonstrate that stable oxygen isotopes in grey mangroves have the potential to yield valuable information about pre-instrumental hydroclimate. Grey mangroves can survive with intact centres for an estimate of >250 years based on observed growth rates, are widespread along northern Australian and tropical coastlines and could provide important information regarding pre-instrumental climate in regions currently lacking high-resolution (i.e., near annual) centennial scale climate proxy records. © 2021 Elsevier B.V.
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    Using stable isotopes and radiocarbon to extract climate information from grey mangroves with non-annual growth rings
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Goodwin, MJ; Verdon-Kidd, DC; Hua, Q; English, NB; Haines, HA; Allen, KJ
    Hydroclimate variability in Australia is not well understood prior to the commencement of instrumental climate records in the mid-20th Century. Instrumental climate records can be extended further back in time using proxy data obtained from annual ring forming trees using dendrochronology. However, aside from several exceptions (e.g., Callitris spp.), suitable trees are rare in mainland Australia. Novel techniques such as bomb-pulse radiocarbon dating and stable isotope analysis have made it possible to obtain climate information from trees that do not form annual growth rings. Grey mangroves (Avicennia marina) are the most common mangrove species in NSW, but their growth layers are non-annual. However, grey mangroves are highly sensitive to climate-related variation in freshwater availability and soil salinity. In this study we demonstrate that radiocarbon-based time series of δ18O and δ13C measured from grey mangroves can be used as hydroclimate proxies. Four grey mangrove stem sections were sampled from dead mangrove trees in the Myall and Hunter River estuaries in NSW, Australia in 2018 and analysed layer-by-layer for δ18O and δ13C using isotope ratio mass spectrometry. Four of the growth layers in each stem including the pith, the outermost layer and two other layers spaced evenly along the selected measurement radius were dated using bomb-pulse radiocarbon dating. A simple age / growth model was prepared for each stem assuming linear growth between the dated layers. Age estimates for all growth layers were truncated to integer calendar years allowing isotope data from the four stems to be averaged into composite δ18O and δ13C series covering the 1962-2016 period. The composite δ18O and δ13C time series were then assessed for similarity with a range of relevant climate variables using Spearman correlation analysis. Significant correlations were found between δ18O and rainfall, days rain, sea level, vapour pressure, Palmer Drought Severity Index (PDSI) and the El Niño Southern Oscillation (ENSO). Grey mangrove δ18O values appear to reflect the relative proportions of assimilated sea water (δ18O ≈ 0‰ VSMOW) and 18O-depleted fresh water entering mangrove wetlands as rainfall and runoff. Higher δ18O values were observed during known droughts in the 1960’s and during the millennium drought, whilst lower δ18O values occurred at the same time as La Niña events in 2010-12, 2007-08, 1998-2001, 1988-89 and 1973-76. The composite δ13C series was positively correlated with temperature, vapour pressure and evapotranspiration, suggesting that grey mangrove δ13C values were primarily influenced by atmospheric moisture demand. The most significant positive δ13C peak occurred at the same time as the intense El Niño drought of 1982/83, and the most significant negative δ13C peak occurred at the same time as the La Niña of 2010-12 that was the wettest 24-month period on record in Australia. These results demonstrate that stable carbon and oxygen isotope ratios in grey mangroves yield valuable hydroclimate information. Grey mangroves can live for up to 800 years, are widespread along northern Australian and tropical coastlines and could provide important information regarding pre-instrumental climate in regions currently lacking highresolution centennial scale climate proxy records. © The Authors