Browsing by Author "Harada, Y"

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    Reconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on record
    (European Geosciences Union (EGU), 2020-02-28) Sippo, JZ; Santos, IR; Sanders, CJ; Gadd, PS; Hua, Q; Lovelock, CE; Santini, NS; Johnston, SG; Harada, Y; Reithmeir, G; Maher, DT
    A massive mangrove dieback event occurred in 2015–2016 along ∼ 1000 km of pristine coastline in the Gulf of Carpentaria, Australia. Here, we use sediment and wood chronologies to gain insights into geochemical and climatic changes related to this dieback. The unique combination of low rainfall and low sea level observed during the dieback event had been unprecedented in the preceding 3 decades. A combination of iron (Fe) chronologies in wood and sediment, wood density and estimates of mangrove water use efficiency all imply lower water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid, large mobilization of sedimentary Fe, which is consistent with redox transitions promoted by changes in soil moisture content. Elemental analysis of wood cross sections revealed a 30- to 90-fold increase in Fe concentrations in dead mangroves just prior to their mortality. Mangrove wood uptake of Fe during the dieback is consistent with large apparent losses of Fe from sediments, which potentially caused an outwelling of Fe to the ocean. Although Fe toxicity may also have played a role in the dieback, this possibility requires further study. We suggest that differences in wood and sedimentary Fe between living and dead forest areas reflect sediment redox transitions that are, in turn, associated with regional variability in groundwater flows. Overall, our observations provide multiple lines of evidence that the forest dieback was driven by low water availability coinciding with a strong El Niño–Southern Oscillation (ENSO) event and was associated with climate change. © Author(s) 2020.
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    Tracking shark spatial mobility patterns using 14C measurements on vertebrae growth bands
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Harada, Y; Gustafson, J; Hua, Q; Riekenberg, PM; Steinhof, A; Fernandes, R
    Information on shark spatial mobility patterns is crucial to understand their feeding ecology and to identify prospective marine protected areas essential for their conservation. In this respect, radiocarbon can make a useful contribution by exploring spatial variations in marine radiocarbon reservoir effects. Here, we report data for seven sharks (1× scalloped hammer head, 1× tiger shark, 2× great hammer head, 3× great white shark) found dead off the Brisbane coastal region in Australia between 2016 and 2019. To examine temporal variations in dwelling areas and feeding habits, separate growth band samples were taken from a vertebra of each specimen for AMS 14C measurements, for carbon and nitrogen stable isotope analyses of bulk collagen, and nitrogen stable isotope analysis of single amino acids. Here we show considerable variability in 14C values among the different specimens and across time for each specimen which is indicative of individual spatial mobility patterns. We will discuss the use of novel Bayesian approaches to map temporal dwelling areas for each specimen by comparing shark vertebrae 14C results with the spatial distribution of surface marine radiocarbon levels effects . This has the potential of offering a new research tool for conservation purposes. © The Authors