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Amy Atkins

Formation, Transformation and Trace-element scavenging of Minerals in Deep-Sea Ferromanganese crusts: Implications for marine biogeochemical cycles and paleoceanography. Amy Atkins. Supervisors: Dr Caroline Peacock & Dr Sam Shaw. Funding Part NERC/ Part SOEE.

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Amy Atkins

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  1. Formation, Transformation and Trace-element scavenging of Minerals in Deep-Sea Ferromanganese crusts: Implications for marine biogeochemical cycles and paleoceanography Amy Atkins Supervisors: Dr Caroline Peacock & Dr Sam Shaw

  2. Funding • Part NERC/ Part SOEE • Academic background Background • 2006-2009: B.Sc. Chemistry -University of Huddersfield • 2009-2010: M.Sc. Geochemistry - University of Leeds • M.S.c. Project : Mineralogical and physiochemical controls on Ni uptake by manganese minerals

  3. Background • Deep-sea hydrothermal vent fluids provide a major source of dissolved Fe and Mn to the deep oceans • Dissolved species react with oxidised seawater to precipitate abundant Fe/Mn (hydr)oxide minerals that form ferromanganese crusts at the sediment-water interface • Precipitates are rich in manganese mineral phases such as, • birnessite and todorokite • These mineral phases have high sorptive capacities and strongly scavenge trace elements from seawater Images courtesy of nasa.gov

  4. Why do we care ? • The formation of these minerals and their scavenging of trace-elements is a key control on the concentration of trace-elements in seawater and ocean sediments • Minerals play a key role in the biogeochemical cycling of trace-elements, including micro-nutrients, at both the regional and global scales. • As the minerals sorb trace-elements from seawater over time, they provide a ready depository for trace-metal chemical information over the entire history of their formation • These chemical signatures may be useful in terms of reconstructing aspects of seawater composition over the earths history.

  5. Project Aims & Objectives • Investigate birnessite and todorokite formation at the molecular level • Examine questions surrounding the transformation of the minerals on the ocean floor • Determine how these minerals sorb key trace-elements from seawater on a molecular scale. • Provide a fundamental new understanding of manganese mineralogy • Provide valuable insight into biogeochemical trace-element cycles in the ocean.

  6. Methodology • Design a series of lab experiments to examine the formation of birnessite and todorokite in the deep ocean. • Employ X-ray spectroscopy and diffraction techniques to investigate the transformation of these mineral phases over time and with temperature and pH. • Perform batch sorption experiments on synthetic mineral phases • Characterise the samples at the molecular level using synchrotron radiation. • Utilise computational modelling programs to aid interpretation of laboratory results.

  7. Any Questions ?

  8. (A) Electrostatic outer-sphere sorption in the Hx-birnessiteinterlayers and todorokite tunnels. (B) Bidentate inner-sphere complexation to the MnOH sites on Hx-birnessite and todorokite. (C) Tridentate inner-sphere complexation above the Mn2O vacancy sites on Hx-binessite. (D) Structural incorporation.

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