White Paper Title: 
Biogeochemistry of iron in hydrothermal plumes

Hydrothermal venting associated with mid-ocean ridge (MOR) volcanism is globally widespread, and responsible for a dissolved iron (Fe) flux to the ocean that is approximately equal to all continental riverine runoff (1). For hydrothermal fluxes, it has long been assumed that most Fe is precipitated as inorganic forms via abiotic processes soon after entering the oceans as hydrothermal plumes. However, recent discoveries from isotopic, voltammetric, and spectroscopic studies prompt us to question these long held assumptions, and point to organic chemistry and biological processes as pivotal for Fe speciation at and transport from MORs (2-6). In particular, a potentially important role for dissolved and particulate organic matter in complexation of Fe in hydrothermal plumes is emerging. These discoveries are opening new avenues of inquiry regarding the properties of organic materials in hydrothermal plume systems and the biogeochemical processes active in the deep-ocean Fe cycle.

Biogeochemical cycling of Fe at MORs is a topic that represents an opportunity for the Ridge community. A critical and concise review of what is known about co-cycling of Fe, carbon, and sulfur at MORs would be valuable contribution because recent discoveries in this area highlight large knowledge gaps. A synthesis of the next big questions would help the community plan for integrated biogeochemical research activities in the context of existing and new programs (e.g. Geotraces and cabled observatories). Research conducted at East Pacific Rise 9-10 o N is particularly attractive for a review because the knowledge generated during R2K for this site is very rich. In addition, there are a number of researchers poised to publish new biogeochemistry research for plumes at EPR: John Breier (7), Christopher German, Olivier Rouxel, Katrina Edwards, Jason Sylvan, Sarah Bennett, and me (Brandy Toner).

1. Elderfield, H. and Schultz, A., 1996. Mid-ocean ridge hydrothermal fluxes and the chemical composition of the ocean. Annu. Rev. Earth Planet. Sci. 24, 191-224.
2. Sander, S. G., Koschinsky, A., Massoth, G. J., Stott, M., and Hunter, K. A., 2007. Organic complexation of copper in deep-sea hydrothermal vent systems. Environ. Chem. 4, 81-89.
3. Chu, N. C., Johnson, C. M., Beard, B. L., German, C. R., Nesbitt, R. W., Frank, M., Bohn, M., Kubik, P. W., Usui, A., and Graham, I., 2006. Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacifiic Ocean through time. Earth Planet. Sci. Lett. 245, 202-217.
4. Bennett, S. A., Achterberg, E. P., Connelly, D. P., Statham, P. J., Fones, G. R., and German, C. R., 2008. The distribution and stabilisation of dissolved Fe in deep-sea hydrothermal plumes. Earth Planet. Sci. Lett. 270, 157-167.
5. Breier, J. A., Rauch, C. G., McCartney, K., Toner, B. M., Fakra, S. C., White, S. N., and German, C. R., 2009. A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters. Deep Sea Research Part I 56, 1579-1589.
6. Toner, B. M., Fakra, S. C., Manganini, S. J., Santelli, C. M., Marcus, M. A., Moffett, J. W., Rouxel, O., German, C. R., and Edwards, K. J., 2009. Preservation of Iron(II) by Carbon-Rich Matrices in Hydrothermal Plumes. Nature Geoscience 2, 197-201.
7. Breier, J. A., Toner, B. M., Fakra, S. C., Marcus, M. A., White, S. N., and German, C. R., submitted. The influence of micro-aggregate formation on deep-sea hydrothermal plume chemistry and particle transport: 9° 50' N East Pacific Rise. Earth and Planetary Science Letters.