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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/bg-2019-478
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-478
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Jan 2020

16 Jan 2020

Review status
A revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Linking climatic-driven iron toxicity and water stress to a massive mangrove dieback

James Z. Sippo1,2, Isaac R. Santos2,3, Christian J. Sanders2, Patricia Gadd4, Quan Hua4, Catherine Lovelock5, Nadia S. Santini6,7, Scott G. Johnston1, Yota Harada8, Gloria Reithmeir1, and Damien T. Maher1,9 James Z. Sippo et al.
  • 1Southern Cross Geoscience, Southern Cross University, Lismore, 2480 Australia
  • 2National Marine Science Centre, Southern Cross University, PO Box 4321, Coffs Harbour, NSW 2450, Australia
  • 3Department of Marine Sciences, University of Gothenburg, Sweden
  • 4Australian Nuclear Science and Technology Organisation (ANSTO), Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
  • 5School of Biological Sciences, the University of Queensland, St Lucia QLD 4072, Australia
  • 6Cátedra Consejo Nacional de Ciencia y Tecnología, Av. Insurgentes Sur 1582, Crédito Constructor, Benito Juárez, 03940, Ciudad de México, Mexico
  • 7Instituto de Ecología, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04500, Ciudad de México, Mexico
  • 8Australian Rivers Institute – Coast and Estuaries, and School of Environment and Science, Griffith University, Gold Coast, QLD 4222, Australia
  • 9School of Environment, Science and Engineering, Southern Cross University, Lismore 2480, Australia

Abstract. A massive mangrove dieback event occurred in 2015/2016 along ~ 1000 km of pristine coastline in the Gulf of Carpentaria, Australia. To gain insights into dieback drivers, we combine sediment and wood chronologies to analyze geochemical and climatic changes. The unique combination of low rainfall and low sea level observed during the dieback event was unprecedented in the previous three decades. Multiple lines of evidence from iron (Fe) chronologies in wood and sediment, wood densities and mangrove water use efficiency suggest low water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid and large mobilization of sedimentary Fe, which was likely associated with pyrite oxidation within mangrove sediments. High resolution elemental analysis of wood cross sections revealed 30–90 fold increase in Fe concentrations in dead mangrove areas just prior to mortality. Fe concentrations in wood samples correlated strongly with the El Niño Southern Oscillation (ENSO) index, suggesting ENSO was a major driver of Fe mobilization. Large Fe losses from sediments during the dieback are consistent with Fe uptake in the trees, further implying sediment pyrite oxidation. If our data are representative of the entire dieback region, we estimate that the dieback drove the mobilization and loss of 50 ± 173 Gg Fe, equivalent to 8–50 % of annual global atmospheric Fe deposition into the oceans, which is one of the major drivers of surface ocean productivity. Overall, our observations support the hypothesis that the forest dieback was associated with low water availability and Fe toxicity driven by a strong ENSO event.

James Z. Sippo et al.

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James Z. Sippo et al.

James Z. Sippo et al.

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Short summary
In 2015/2016, a massive mangrove dieback event occurred along ~ 1000 km of coastline in Australia. Multiple lines of evidence from climate data, wood and sediment samples suggest low water availability within the dead mangrove forest. Wood and sediments also reveal a large increase in iron concentrations in mangrove sediments during the dieback. This study support the hypothesis that the forest dieback was associated with low water availability and iron toxicity driven by a strong ENSO event.
In 2015/2016, a massive mangrove dieback event occurred along ~ 1000 km of coastline in ...
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