The global mid-ocean ridge (MOR) system is a 60,000 km submarine volcanic mountain range that crosses all of the major ocean basins on Earth. Along the MOR, subseafloor seawater circulation exchanges heat and elements between the oceanic crust and seawater. One of the elements released through this venting process is iron. The amount of iron released by hydrothermal venting to the ocean per year (called a flux) is similar in magnitude to that in global riverine runoff (Elderfield and Schultz, 1996). Until recently, measurements and modeling activities to understand the contribution of hydrothermal iron to the ocean budget have been largely neglected. It was thought that hydrothermal iron was removed completely from seawater by precipitation of iron-bearing minerals within plumes and then deposited at the seafloor close to vent sites. With this assumption in place, the contribution of hydrothermal fluxes to the ocean budget was considered negligible. Recent work, however, questions the validity of that assumption, and leads to what we call the "leaky vent" hypothesis. Our goal is to measure the forms of iron, known as speciation, present in hydrothermal plume particles to better understand the bioavailability, geochemical reactivity, and transport properties of hydrothermal iron in the ocean.

Toner, B.M., M.A. Marcus, K.J. Edwards, O. Rouxel, and C.R. German. 2012. Measuring the form of iron in hydrothermal plume particles. Oceanography 25(1):209–212, https://doi.org/10.5670/oceanog.2012.19.

Adams, D.K., D.J. McGillicuddy Jr., L. Zamudio, A.M. Thurnherr, X. Liang, O. Rouxel, C.R. German, and L.S. Mullineaux. 2011. Surface-generated mesoscale eddies transport deep-sea products from hydrothermal vents. Science 332:580–583, https://doi.org/10.1126/science.1201066.
1. Bennett, S.A., E.P. Achterberg, D.P. Connelly, P.J. Statham, G.R. Fones, and C.R. German. 2008. The distribution and stabilisation of dissolved Fe in deep-sea hydrothermal plumes. Earth and Planetary Science Letters 270:157–167, https://doi.org/10.1016/j.epsl.2008.01.048.
2. Breier, J.A., C.G. Rauch, K. McCartney, B.M. Toner, S.C. Fakra, S.N. White, and C.R. German. 2009. A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters. Deep-Sea Research Part I 56:1,579–1,589, https://doi.org/10.1016/j.dsr.2009.04.005.
3. Campbell, A.C. 1991. Mineralogy and chemistry of marine particles by synchrotron X-ray spectroscopy, Mossbauer spectroscopy, and plasma-mass spectrometry. Pp. 375–390 in Marine Particles: Analysis and Characterization. D.C. Hurd and D.W. Spencer, eds, American Geophysical Union, Washington, DC.
4. Chu, N.C., C.M. Johnson, B.L. Beard, C.R. German, R.W. Nesbitt, M. Frank, M. Bohn, P.W. Kubik, A. Usui, and I. Graham. 2006. Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacific Ocean through time. Earth and Planetary Science Letters 245:202–217, https://doi.org/10.1016/j.epsl.2006.02.043.
5. Elderfield, H., and A. Schultz. 1996. Mid-ocean ridge hydrothermal fluxes and the chemical composition of the ocean. Annual Review of Earth and Planetary Sciences 24:191–224, https://doi.org/10.1146/annurev.earth.24.1.191.
6. Feely, R.A., M. Lewison, G.J. Massoth, G. Rober-Baldo, J.W. Lavelle, R.H. Byrne, K.L. Von Damm, and H.C. Curl. 1987. Composition and dissolution of black smoker particulates from active vents on the Juan de Fuca Ridge. Journal of Geophysical Research 92:11,347–11,363.
7. Lam, P.J., D.C. Ohnemus, and M.A. Marcus. 2012. The speciation of marine particulate iron adjacent to active and passive continental margins. Geochimica et Cosmochimica Acta, https://doi.org/10.1016/j.gca.2011.11.044.
8. Lilley, M.D., R.A. Feely, and J.H. Trefry. 1995. Chemical and biochemical transformations in hydrothermal plumes. Pp. 369-391 in Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions. S.E. Humphris, R.A. Zierenberg, L.S. Mullineaux, and R.E. Thomson, eds, Geophysical Monograph Series, vol. 91, American Geophysical Union, Washington, DC, https://doi.org/10.1029/GM091p0369.
9. Lupton, J.E. 1998. Hydrothermal helium plumes in the Pacific Ocean. Journal of Geophysical Research 103:15,853–15,868, https://doi.org/10.1029/98JC00146.
10. Marcus, M.A., A. MacDowell, R. Celestre, A. Manceau, T. Miller, H.A. Padmore, and R.E. Sublett. 2004. Beamline 10.3.2 at ALS: A hard X-ray microprobe for environmental and material sciences. Journal of Synchrotron Radiation 11:239–247.
11. Mayhew, L.E., S.M. Webb, and A.S. Templeton. 2011. Microscale imaging and identification of Fe oxidation state, speciation, and distribution in complex geological media. Environmental Science & Technology 45:4,468–4,472, https://doi.org/10.1021/es104292n.
12. McGillicuddy, D.J. Jr., L.A. Anderson, N.R. Bates, T. Bibby, K.O. Buesseler, C.M. Carlson, C.S. Davis, C. Ewart, P.G. Falkowski, S.A. Goldthwait, and others. 2007. Eddy/wind interactions stimulate extraordinary mid-ocean plankton blooms. Science 316:1,021–1,026, https://doi.org/10.1126/science.1136256.
13. Sander, S.G., and A. Koschinsky. 2011. Metal flux from hydrothermal vents increased by organic complexation. Nature Geoscience 4:145–150, https://doi.org/10.1038/ngeo1088.
14. Tagliabue, A., L. Bopp, J.-C. Dutay, A.R. Bowie, F. Chever, P. Jean-Baptiste, E. Bucciarelli, D. Lannuzel, T. Remenyi, G. Sarthou, and others. 2010. Hydrothermal contribution to the oceanic dissolved iron inventory. Nature Geoscience 3:252–256, https://doi.org/10.1038/ngeo818.
15. Toner, B.M., S.C. Fakra, S.J. Manganini, C.M. Santelli, M.A. Marcus, J.W. Moffett, O. Rouxel, C.R. German, and K.J. Edwards. 2009b. Preservation of iron(II) by carbon-rich matrices in hydrothermal plumes. Nature Geoscience 2:197–201, https://doi.org/10.1038/ngeo433.
16. Winckler, G., R. Newton, P. Schlosser, and T.J. Crone. 2010. Mantle helium reveals Southern Ocean hydrothermal venting. Geophysical Research Letters 37, L05601, https://doi.org/10.1029/2009GL042093.
17. Wu, J., M.L. Wells, and R. Rember. 2011. Dissolved iron anomaly in the deep tropical-subtropical Pacific: Evidence for long-range transport of hydrothermal iron. Geochimica et Cosmochimica Acta 75:460–468, https://doi.org/10.1016/j.gca.2010.10.024.
18. Yücel, M., A. Gartman, C.S. Chan, and G.W. Luther III. 2011. Hydrothermal vents as a kinetically stable source of iron-sulphide-bearing nanoparticles to the ocean. Nature Geoscience 4:367–371, https://doi.org/10.1038/ngeo1148.

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