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 Academic background Background : B.Sc. Chemistry -University of Huddersfield : M.Sc. Geochemistry - University of Leeds M.S.c. Project : Mineralogical and physiochemical controls on Ni uptake by manganese minerals

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 Background Images courtesy of nasa.gov

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. Why do we care ?

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.

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. Methodology

Any Questions ?

(A) Electrostatic outer-sphere sorption in the Hx-birnessite interlayers and todorokite tunnels. (B) Bidentate inner-sphere complexation to the MnOH sites on Hx-birnessite and todorokite. (C) Tridentate inner-sphere complexation above the Mn 2 O vacancy sites on Hx-binessite. (D) Structural incorporation.