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Instruments / Technical Area	Publication Details	Published
I08-Scanning X-ray Microscopy beamline (SXM)	The role and fate of organic carbon during aging of ferrihydrite Yao Zhao , Oliver W. Moore , Ke-Qing Xiao , Lisa Curti , Alba Otero-Farina , Steven A. Banwart , Caroline L. Peacock Geochimica Et Cosmochimica Acta 212 DOI: 10.1016/j.gca.2022.07.003 Diamond Proposal Number(s): [23049] Open Access Show Abstract ▼ Abstract: The persistence of organic carbon (OC) in natural environments is widely attributed to mineral protection, especially by iron (Fe) (oxyhydr)oxides. The effect of OC binding strength on the aging of Fe (oxyhydr)oxides and the mobility and fate of OC during aging however, is unknown. Here we investigate how OC binding strength controls the aging of ferrihydrite (Fh) and subsequent retention or release of the associated OC. We focus on carboxyl-rich OC coprecipitated with Fh and track the physiochemical properties and OC stability as a function of carboxyl-richness over time. In agreement with previous work we find that during carboxyl-rich OC coprecipitation with Fh, OC is adsorbed to the Fh particle surfaces and that increasing carboxyl-richness results in an increasing number of carboxylate-Fe bonds between the OC and the mineral particles and thus increasing OC binding strength. We show that OC substantially retards the aging of Fe (oxyhydr)oxide from Fh to more crystalline Fe minerals and that this retardation increases with increasing OC binding strength. We also show that the total amount of OC decreases during aging and that the proportion of the remaining OC that is non-desorbable with 0.1 M NaOH decreases during aging for OC with relatively low binding strength but increases during aging for OC with relatively high binding strength. Our results therefore indicate that OC with higher binding strength coprecipitated with Fh becomes proportionally more stable with the solid phase and thus less mobile during aging in natural environments. We suggest that our work might offer a deeper mechanistic insight into the processes responsible for OC persistence with minerals and thus the long-term preservation of OC in natural environments.	Jul 2022
I08-Scanning X-ray Microscopy beamline (SXM)	Mineralogical control on methylotrophic methanogenesis and implications for cryptic methane cycling in marine surface sediment Ke-Qing Xiao , Oliver W. Moore , Peyman Babakhani , Lisa Curti , Caroline L. Peacock Nature Communications 13 DOI: 10.1038/s41467-022-30422-4 Diamond Proposal Number(s): [20839] Open Access Show Abstract ▼ Abstract: Minerals are widely proposed to protect organic carbon from degradation and thus promote the persistence of organic carbon in soils and sediments, yet a direct link between mineral adsorption and retardation of microbial remineralisation is often presumed and a mechanistic understanding of the protective preservation hypothesis is lacking. We find that methylamines, the major substrates for cryptic methane production in marine surface sediment, are strongly adsorbed by marine sediment clays, and that this adsorption significantly reduces their concentrations in the dissolved pool (up to 40.2 ± 0.2%). Moreover, the presence of clay minerals slows methane production and reduces final methane produced (up to 24.9 ± 0.3%) by a typical methylotrophic methanogen—Methanococcoides methylutens TMA-10. Near edge X-ray absorption fine structure spectroscopy shows that reversible adsorption and occlusive protection of methylamines in clay interlayers are responsible for the slow-down and reduction in methane production. Here we show that mineral-OC interactions strongly control methylotrophic methanogenesis and potentially cryptic methane cycling in marine surface sediments.	May 2022
I08-Scanning X-ray Microscopy beamline (SXM)	Carboxyl-richness controls organic carbon preservation during coprecipitation with iron (oxyhydr)oxides in the natural environment Lisa Curti , Oliver W. Moore , Peyman Babakhani , Ke-Qing Xiao , Clare Woulds , Andrew W. Bray , Ben J. Fisher , Majid Kazemian , Burkhard Kaulich , Caroline L. Peacock Communications Earth & Environment 2 DOI: 10.1038/s43247-021-00301-9 Diamond Proposal Number(s): [21323, 20839, 23049] Open Access Show Abstract ▼ Abstract: The coprecipitation of organic carbon with iron minerals is important for its preservation in soils and sediments, but the mechanisms for carbon-iron interactions and thus the controls on organic carbon cycling are far from understood. Here we coprecipitate carboxylic acids with iron (oxyhydr)oxide ferrihydrite and use near-edge X-ray absorption fine structure spectroscopy and wet chemical treatments to determine the relationship between sequestration mechanism and organic carbon stability against its release and chemical oxidative remineralisation. We show that organic carbon sequestration, stabilisation and persistence increase with an increasing number of carboxyl functional groups. We suggest that carboxyl-richness provides an important control on organic carbon preservation in the natural environment. Our work offers a mechanistic basis for understanding the stability and persistence of organic carbon in soils and sediments, which might be used to develop an overarching relationship between organic functional group-richness, mineral interactions and organic carbon preservation in the Earth system.	Nov 2021

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