Carbon sequestration processes in the rusty carbon sink


   School of Biological & Environmental Sciences

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  Dr C Schroeder, Prof Jaime Toney  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Carbon is sequestered in soils and sediments via mineral associations. Over 20% of organiccarbon in sediments is directly bound to reactive iron mineral phases, giving rise to the so-called ‘rusty carbon sink’ (Lalonde et al. 2012). In a world of global environmental change,we need to understand how the rusty carbon sink reacts to changing environmentalconditions such as ocean acidification, increasing temperatures, sea level rise, or enhancedrainfall and drought events.

The global biogeochemical iron cycle controls the carbon cycle (Raiswell and Canfield 2012).For example, iron is a limiting nutrient for phytoplankton growth in large areas of the ocean(Moore et al. 2013; Tagliabue et al. 2017), and more than 20% of organic carbonsequestered in sediments are directly bound to reactive iron mineral phases (Lalonde et al.2012). While some organic compounds such as citrate are specifically excreted bymicroorganisms to reduce and dissolve iron oxides, other organic compounds such as humicsubstances have no such effect (Braunschweig et al. 2014). Instead, when binding to themineral surface, they appear to result in mutual stabilization of both the reactive iron mineraland the organic carbon compound: the organic compounds are protected against microbialprocessing and redox processes and the reactive iron minerals are protected against mineraltransformations. Diagenetic processes (increased heat and pressure) eventually lead todehydration and reduction of the reactive iron minerals while the carbon compounds areoxidized into carbonate (Posth et al. 2013). However, even under diagenetic conditions, agreater presence of organic compounds slows down the mineral transformation (Schröder etal. 2016). To understand this stabilization is important in particular in light of globalenvironmental change: Where can we enhance carbon storage through such processes andwhere are existing carbon sinks at risk through changing environmental conditions (e.g.ocean acidification and warming temperatures).

Reactive iron minerals tend to be metastable and it is hypothesized that reactive ironminerals and certain organic compounds mutually stabilize each other (e.g. Schröder et al.2016): the organic compounds are protected against microbial processing and redoxprocesses and the reactive iron minerals are protected against mineral transformations. Inthis project, we aim to understand how the mutual stabilization works. What types of organiccompounds and functional groups enhance this stabilization (Hu et al. 2023; Zhao et al.2023)? Are different kinds of reactive iron minerals more efficient in preserving organiccarbon that way than others? What environmental factors increase or decrease thisstabilization?

In this project, we will investigate sediments collected from different coastal and marinesettings and compare those to experimental setups in the laboratory, in which we willinvestigate reaction pathways of iron minerals and organic compounds. Specifically, we willstudy mineral transformations via Mössbauer spectroscopy, using the stable 57Fe isotopesas a trace to understand reaction pathways (Notini et al. 2023), and use advanced methodsto identify the organic compounds binding to these minerals.


Chemistry (6) Environmental Sciences (13) Geology (18) Physics (29)

Funding Notes

IAPETUS2’s postgraduate studentships are tenable for up to 3.5 years and provide the following package of financial support:
• A tax-free maintenance grant set at the UK Research Council’s national rate, which in 2023/24 is £18,622;
• Payment of tuition fees at the Home rate (some of our partners have funding available for the additional fees charged to international students);
• Access to extensive research support funding; &
• Support for an external placement of up to six months.
Part-time award-holders are funded for seven years and receive a maintenance grant at 50% of the full-time rate.

References

Braunschweig, J., C. Klier, C. Schröder, M. Händel, J. Bosch, K.U. Totsche, and R.U.Meckenstock (2014), Citrate influences microbial Fe hydroxide reduction via a dissolution-disaggregation mechanism, Geochimica et Cosmochimica Acta 139, 434–446,http://dx.doi.org/10.1016/j.gca.2014.05.006.
Gütlich, P. and C. Schröder (2012), Mössbauer Spectroscopy. In: Methods in PhysicalChemistry, edited by R. Schäfer and P.C. Schmidt, Wiley-VCH, pp. 351-389,http://dx.doi.org/10.1002/9783527636839.ch11.
P. Gütlich , C. Schröder, and V. Schünemann (2012), Mössbauer Spectroscopy – Anindispensable tool in solid state research, Spectroscopy Europe 24(4), 21-32,https://www.spectroscopyeurope.com/article/m%C3%B6ssbauer-spectroscopy%E2%80%94-indispensable-tool-solid-state-research.
Hu L, Ji Y, Zhao B, Liu X, Du J, Liang Y, Yao P. (2023). The effect of iron on the preservationof organic carbon in marine sediments and its implications for carbon sequestration. ScienceChina Earth Sciences, 66, https://doi.org/10.1007/s11430-023-1139-9.
Lalonde et al (2012) Preservation of organic matter in sediments promoted by iron. Nature483, 198–200, doi:10.1038/nature10855.5/6
Moore et al (2013) Processes and patterns of oceanic nutrient limitation. Nature Geoscience6, 701–710, doi:10.1038/NGEO1765.
Notini et al. (2023), A New Approach for Investigating Iron Mineral Transformations in Soilsand Sediments Using 57Fe-Labeled Minerals and 57Fe Mössbauer Spectroscopy,Environmental Science & Technology in press, https://doi.org/10.1021/acs.est.3c00434.
Posth, N.R. I. Köhler, E. Swanner, C. Schröder, E. Wellmann, B. Binder, K. O. Konhauser, U.Neumann, C. Berthold, M. Nowak, and A. Kappler (2013), Simulating Precambrian bandediron formation diagenesis, Chemical Geology, 362, 66-73,http://dx.doi.org/10.1016/j.chemgeo.2013.05.031.
Raiswell and Canfield (2012) The iron biogeochemical cycle past and present. GeochemPerspect 1, 1–220, doi:10.7185/geochempersp.1.1.
Schröder, C., I. Köhler, F.L.L. Muller, A.I. Chumakov, I. Kupenko, Rudolf Rüffer, and A.Kappler (2016), The biogeochemical iron cycle and astrobiology, Hyperfine Interactions 237,85, http://dx.doi.org/10.1007/s10751-016-1289-2.
Tagliabue et al (2017) The integral role of iron in ocean biogeochemistry. Nature 543, 5 1-59,doi:10.1038/nature21058.
Zhao, B., P. Yao, T.S. Bianchi, X. Wang, M.R. Shields, C. Schröder, and Z. Yu (2023),Preferential preservation of pre-aged terrestrial organic carbon by reactive iron in estuarineparticles and coastal sediments of a large river-dominated estuary, Geochimica etCosmochimica Acta 345, 34–49, https://doi.org/10.1016/j.gca.2023.01.023.

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