Browsing by Author "Sanders, CJ"

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    Are mangrove carbon exports old or modern? A multiple radio- and stable isotope analysis
    (University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-09) Maher, DT; Call, M; Santos, IR; Sanders, CJ; Schulz, KG; Jenkinson, A; Jacobsen, GE
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    Blue carbon oxidation revealed by radiogenic and stable isotopes in a mangrove system
    (American Geophysical Union, 2017-05-8) Maher, DT; Santos, IR; Schulz, KG; Call, M; Jacobsen, GE; Sanders, CJ
    Mangroves are among the most carbon-rich ecosystems on Earth and can sequester carbon in sediments over long timescales. Here we assess whether century-old buried carbon may be remineralized and exported by measuring Δ14C in the exported dissolved inorganic carbon (DIC) as well as sediment Δ14C profiles in a subtropical mangrove. Pore water exchange released isotopically depleted, old DIC to surface waters. Keeling plots revealed that the source of DIC to surface waters had a δ13C-DIC value of −29.4 ±1.9‰ and Δ14C-DIC value of −73±9‰. The respired and exported carbon comes from an average depth of ~40 cm, equivalent to ~100 years of sediment accumulation. Therefore, century-old sequestered carbon is still susceptible to remineralization and tidal export to the coastal ocean via pore water exchange or submarine groundwater discharge. We suggest that the timescales over which blue carbon burial is assessed should consider carbon losses via pore water exchange. © 2017. American Geophysical Union
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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.