Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 3 2010 10.5194/bg-7-827-2010 http://www.biogeosciences.net/7/827/2010/ http://www.biogeosciences.net/7/827/2010/bg-7-827-2010.html http://www.biogeosciences.net/7/827/2010/bg-7-827-2010.pdf 827 844 2010-03-03 The role of airborne volcanic ash for the surface ocean biogeochemical iron-cycle: a review S. Duggen svend_duggen@skoleforeningen.de N. Olgun P. Croot L. Hoffmann H. Dietze P. Delmelle C. Teschner IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Dynamics of the Ocean Floor, Wischhofstrasse 1–3, 24148 Kiel, Germany A. P. Møller Skolen, Upper Secondary School and Sixth Form College of the Danish National Minority in Germany, Fjordallee 1, 24837 Schleswig, Germany IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Marine Biogeochemistry, Düsternbrooker Weg 20, 24105 Kiel, Germany Department of Plant and Environmental Sciences, Göteborg University, Carl Skottsberg Gata 22 B, 40530 Gothenburg, Sweden Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand Environment Department, University of York, Heslington Y010 5DD, York, UK IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Ocean Circulation and Climate Dynamics, Wischhofstrasse 1–3, 24148 Kiel, Germany Iron is a key micronutrient for phytoplankton growth in the surface ocean. Yet the significance of volcanism for the marine biogeochemical iron-cycle is poorly constrained. Recent studies, however, suggest that offshore deposition of airborne ash from volcanic eruptions is a way to inject significant amounts of bio-available iron into the surface ocean. Volcanic ash may be transported up to several tens of kilometers high into the atmosphere during large-scale eruptions and fine ash may stay aloft for days to weeks, thereby reaching even the remotest and most iron-starved oceanic regions. Scientific ocean drilling demonstrates that volcanic ash layers and dispersed ash particles are frequently found in marine sediments and that therefore volcanic ash deposition and iron-injection into the oceans took place throughout much of the Earth's history. Natural evidence and the data now available from geochemical and biological experiments and satellite techniques suggest that volcanic ash is a so far underestimated source for iron in the surface ocean, possibly of similar importance as aeolian dust. Here we summarise the development of and the knowledge in this fairly young research field. The paper covers a wide range of chemical and biological issues and we make recommendations for future directions in these areas. The review paper may thus be helpful to improve our understanding of the role of volcanic ash for the marine biogeochemical iron-cycle, marine primary productivity and the ocean-atmosphere exchange of CO₂ and other gases relevant for climate in the Earth's history. % vor jede Referenz Awaya, Y., Kodani, E., Tanaka, K., Liu, J., Zhuang, D., and Meng, Y.: Estimation of the global net primary productivity using NOAA images and meteorological data: changes between 1988 and 1993, Int. J. Remote Sens., 25, 1597–1613, 2004. Bains, S., Norris, R. D., Corfield, R. M., and Faul, K. L.: Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback, Nature, 407, 171–174, 2000. Baker, A. R. and Croot, P. L.: Atmospheric and marine controls on aerosol iron solubility in seawater, Mar. Chem., doi:10.1016/j.marchem.2008.09.003, in press, 2010. Banse, K. and English, D. C.: Comparing phytoplankton seasonality in the eastern and western subarctic Pacific and the western Bering sea, Prog. Oceanogr., 43, 235–288, 1999. Bay, R. C., Bramall, N., and Price, P. B.: Bipolar correlation of volcanism with millenial climate change, Proceedings of the National Academy of Science of the United States of America, 101, 6341–6345, 2004. Bay, R. C., Bramall, N. E., Price, P. B., Clow, G. D., Hawley, R. L., Udisti, R., and Castellano, E.: Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period, J. Geophys. Res., 111, D11108, doi:10.1029/2005JD006306, 2006. Behrenfeld, M. J., Bale, A. J., Kolber, Z. S., Aiken, J., and Falkowski, P. G.: Confirmation of iron limitation of phytoplankton photosynthesis in the equatorial Pacific Ocean, Nature, 383, 508–511, 1996. Benitez-Nelson, C. R., Vink, S. M., Carrillo, J. H., and Huebert, B. J.: Volcanically influenced iron and aluminium cloud water deposition to Hawaii, Atmos. Environ., 37, 535–544, 2003. Blain, S., Quéguiner, B., Armand, L., Belviso, S., Bombled, B., Bopp, L., Bowie, A., Brunet, C., Brussaard, C., Carlotti, F., Christaki, U., Corbière, A., Durand, I., Ebersbach, F., Fuda, J.-L., Garcia, N., Gerringa, L., Griffiths, B., Guigue, C., Guillerm, C., Jaquet, S., Jeandel, C., Laan, P., Lefèvre, D., Monaco, C. L., Malits, A., Mosseri, J., Obernosterer, I., Park, Y.-H., Picheral, M., Pondaven, P., Remenyi, T., Sandroni, V., Sarthou, G., Savoye, N., Scouarnec, L., Souhaut, M., Thuiller, D., Timmermans, K., Trull, T., Uitz, J., van Beel, P., Veldhuis, M., Vincent, D., Viollier, E., Vong, L., and Wagener, T.: Effect of natural iron fertilization on carbon sequestration on the Southern Ocean, Nature, 446, 1070–1074, 2007. Boyd, P. W., Watson, A. J., Law, C. S., Abraham, E. R., Trull, T., Murdoch, R., Bakker, D. C. E., Bowie, A. R., Buesseler, K. O., Chang, H., Charette, M., Croot, P., Downing, K., Frew, R., Gall, M., Hadfield, M., Hall, J., Harvey, M., Jameson, G., LaRoche, J., Liddicoat, M. I., Ling, R., Maldonado, M. T., McKay, R. M., Nodder, S., Pickmere, S., Pridmore, R., Rintoul, S., Safi, K., Sutton, P., Strzepek, R., Tanneberger, K., Turner, S., Waite, A., and Zeldis, J.: A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization, Nature, 407, 695–702, 2000. Boyd, P. W., Law, C. S., Wong, C. S., Nojiri, Y., Tsuda, A., Levasseur, M., Takeda, S., Rivkin, R., Harrison, P. J., Strzepek, R., Gower, J., McKay, R. M., Abraham, E. R., Arychuk, M., Barwell-Clarke, J., Crawford, W., Crawford, D., Hale, M., Harada, K., Johnson, K., Kiyosawa, H., Kudo, I., Marchetti, A., Miller, W., Needoba, J., Nishioka, J., Ogawa, H., Page, J., Robert, M., Saito, H., Sastri, A., Sherry, N., Soutar, T., Sutherland, N., Taira, Y., Whitney, F., Wong, S.-K. E., and Yoshimura, T.: The decline and fate of an iron-induced subarctic phytoplankton bloom, Nature, 428, 549–553, 2004. Bruland, K. W. and Lohan, M. C.: Controls of trace metals in seawater, in: The Oceans and Marine Geochemistry, edited by: Elderfield, H., Treatise on Geochemistry, Elsevier Pergamon, Amsterdam-Boston-Heidelberg-London-New York-Oxford-Paris-San Diego-San Francisco-Singapore-Sydney-Tokyo, 23–47, 2004. Capaccioni, B. and Mangani, F.: Monitoring of active but quiescent volcanoes using light hydrocarbon distribution in volcanic gases: the results of 4 years of discontinuous monitoring in the Campi Flegrei (Italy), Earth Planet. Sci. Lett., 188, 543–555, 2001. Cather, S. M., Dunbar, N. W., McDowell, F. W., McIntosh, W. C., and Scholle, P. A.: Climate forcing by iron fertilization from repeated ignimbrite eruptions: The icehouse-silicic large igneous province (SLIP) hypothesis, Geosphere, 5, 315–324, 2009. Christenson, B. W.: Geochemistry of fluids associated with the 1995–1996 eruption of Mt. Ruapehu, New Zealand: signatures and processes in the magmatic-hydrothermal system, J. Volcanol. Geoth. Res., 97, 1–30, 2000. Cimino, G. and Toscano, G.: Dissolution of trace metals from lava ash: influence on the composition of rainwater in the Mount Etna volcanic area, Environ. Pollut., 99, 389–393, 1998. Coale, K. H., Johnson, K. S., Fitzwater, S. E., Gordon, R. M., Tanner, S. J., Chavez, F. P., Ferioli, L., Sakamoto, C., Rogers, P., Millero, F., Steinberg, P., Nightingale, P., Cooper, D., Cochlan, W. P., Landry, M. R., Constantiniou, J., Rollwagen, G., Trasvina, A., and Kudela, R.: A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean, Nature, 383, 495–501, 1996. Coale, K. H., Johnson, K. S., Chavez, F. P., Buesseler, K. O., Barber, R. T., Brzezinski, M. A., Cochlan, W. P., Millero, F., Falkowski, P. G., Bauer, J. E., Wanninkhof, R. H., Kudela, R. M., Altabet, A. M., Hales, B. E., Takahashi, T., Landry, M. R., Bidigare, R. R., Wang, X., Chase, Z., Strutton, P. G., Friederich, G. E., Gorbunov, M. Y., Lance, V. P., Hilting, A. K., Hiscock, W. T., Sullivan, K. F., Tanner, S. J., Gordon, R. M., Hunter, C. N., Elrod, V. A., Fitzwater, S. E., Jones, J. L., Tozzi, S., Koblizek, M., Roberts, A. E., Herndon, J., Brewster, J., Ladizinsky, N., Smith, G., Cooper, D., Timothy, D., Brown, S. L., Selph, K. E., Sheridan, C. C., Twining, B. S., and Johnson, Z. I.: Southern Ocean iron enrichment experiment: Carbon cycling in high- and low-Si waters, Science, 304, 408–414, 2004. Cooper, D. J., Watson, A. J., and Nightingale, P. D.: Large decrease in ocean-surface CO₂ fugacity in response to \textitin situ iron fertilization, Nature, 383, 511–513, 1996. Croot, P. and Johansson, M.: Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-$p$-creasol (TAC), Electroanalysis, 12, 565–576, 2000. De Baar, J. W. O. and De Jong, J. T. M.: Distributions, Sources and Sinks of Iron in Seawater, in: Biogeochemistry of iron in seawater, edited by: Turner, D. R. and Hunter, K., Wiley, Chichester, 124–233, 2001. de Hoog, J. C. M., Koetsier, G. W., Bronto, S., Sriwana, T., and van Bergen, M. J.: Sulfur and chlorine degassing from primitive arc magmas: temporal changes during the 1982-1963 eruptions of Galunggung (West Java, Indonesia), J. Volcanol. Geoth. Res., 108, 55–83, 2001. Delmelle, P., Lambert, M., Dufrene, Y., Gerin, P., and Óskarsson, N.: Gas/aerosol-ash interaction in volcanic plumes: New insights from surface analyses of fine ash particles, Earth Planet. Sci. Lett., 259, 159–170, 2007. Duggen, S., Croot, P., Schacht, U., and Hoffmann, L.: Subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth: Evidence from biogeochemical experiments and satellite data, Geophys. Res. Lett., 34(5), L01612, doi:10.1029/2006GL027522, 2007. Eicher, G. J. and Rounsefell, G. A.: Effects of lake fertilization by volcanic activity on abundance of salmon, Limnol. Oceanogr., 2, 70–76, 1957. Felitsyn, S. B. and Kirianov, V. Y.: Mobility of phosphorous during weathering of volcanic ashes, Lithol. Miner. Resour., 37, 275–278, 2002. Fisher, R. V. and Schmincke, H.-U.: Pyroclastic Rocks, Springer-Verlag, Berlin-Heidelberg-New York-Tokyo, 472~pp., 1984. Flaathen, T. K., Oelkers, E. H., and Gislason, S. R.: The effect of aqueous sulphate on basaltic glass dissolution rates, Mineralogical Magazine, 72, 39–41, 2008. Frogner Kockum, P. C.: A diverse ecosystem response to volcanic aerosols, Chem. Geol., 231, 57–66, 2006. Frogner, P., Gislason, S. R., and Oskarsson, N.: Fertilization Potential of Volcanic Ash in Ocean Surface Waters, Journal of Conference Abstracts (Goldschmidt Conference 2000, Oxford), 5, 415, 2000. Frogner, P., Gíslason, S. R., and Óskarsson, N.: Fertilizing potential of volcanic ash in ocean surface water, Geology, 29, 487–490, 2001. Fruchter, J. S., Robertson, D. E., Evans, J. C., Olsen, K. B., Lepel, E. A., Laul, J. C., Abel, K. H., Sanders, R. W., Jackson, P. O., Wogman, N. S., Perkins, R. W., van Tuyl, H. H., Beauchamp, R. H., Shade, J. W., Daniel, J. L., Erikson, R. L., Sehmel, G. A., Lee, R. N., Robinson, A. V., Moss, O. R., Briant, J. K., and Cannon, W. C.: Mount St. Helens Ash from the 18 May 1980 Eruption: Chemical, Physical, Mineralogical, and Biological Properties, Science, 209, 1116–1125, 1980. Gislason, S. R. and Oelkers, E. H.: Mechanism, rates, and consequences of basaltic glass dissolution: II. An experimental study of the dissolution rates of basaltic glass as a function of pH and temperature, Geochim. Cosmochim. Acta, 67, 3817–3832, 2003. Gran, H. H.: On the conditions for the production of plankton in the sea, Rapp. Proc. Verb. Cons. Int. Explor. Mer, 75, 37–46, 1931. Harvey, H. W.: The supply of iron to diatoms, Journal of the Marine Biology Association, XXII, 205–219, 1937. Jicha, B. R., Scholl, D. W., and Rea, D. K.: Circum-Pacific arc flare-ups and global cooling near the Eocene-Oligocene boundary, Geology, 37, 303–306, doi:10.1130/G25392A.1, 2009. Jones, M. T. and Gislason, S. R.: Rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments, Geochim. Cosmochim. Acta, 72, 3661–3680, 2008. Keeling, R. F., Piper, S. C., and Heimann, M.: Global and hemispheric CO₂ sinks deduced from changes in atmospheric O₂ concentration, Nature, 381, 218–221, 1996. Kraemer, S. M.: Iron oxide dissolution and solubility in the presence of siderophores, Aquat. Sci., 66, 3–18, 2004. Krakauer, N. Y. and Randerson, J. T.: Do volcanic eruptions enhance or diminish net pimary production? Evidence from tree rings, Global Biogeochem. Cy., 17, 002003, doi:10.1029/2003GB002076, 2003. Kunz-Pirrung, M., Gersonde, R., and Hodell, D. A.: Mid-Brunhes century-scale diatom sea surface temperature and sea ice records from the Atlantic sector of the Southern Ocean (ODP Leg 177, sites 1093, 1094 and core PS2089-2), Palaegeogr. Palaeocl., 182, 305–328, 2002. Kurenkov, I. I.: The influence of volcanic ashfall on biological processes in a lake, Limnol. Oceanogr., 11, 426–429, 1966. Kutterolf, S., Freundt, A., and Peréz, W.: Pacific offshore record of plinian arc volcanism in Central America: 2. Tephra volumes and erupted masses, Geochem. Geophy. Geosy., 9, 1–19, 2008. Langmann, B., Zakšek, K., Hort, M., and Duggen, S.: Volcanic ash as fertiliser for the surface ocean, Atmos. Chem. Phys. Discuss., 10, 711–734, 2010. Larsson, W.: Vulkanische Asche vom Ausbrauch des chilenischen Vulkans Quizapu (1932) in Argentinien gesammelt. Eine Studie über äolische Differentiation., Geological Institute of Upsala Bulletin, 26, 27–52, 1937. Lepskaya, E. V.: Influence of Ash from the Alaid Volcano on Phytoplankton of Lake Kurile (Southern Kamchatka), in: Issledovaniya biologii i dinamiki chislennosti promyslovykh ryb Kamchatskogo shel'fa (The Study of Biology and Dynamics of Commercial Fish Population on the Kamchatka Shelf), 2, Min-vo Rybn, Khoz-va, Petropavlovsk-Kamchatskii, 21–24, 1993. Lucht, W., Prentice, I. C., Myneni, R. B., Sitch, S., Friedlingsstein, P., Cramer, W., Bousquet, P., Buermann, W., and Smith, B.: Climatic control of the high-latitude vegetation greening trend and Pinatubo effect, Science, 296, 1687–1689, 2002. Martin, J. H. and Fitzwater, S. E.: Iron deficiency limits phytoplankton growth in the north-east Pacific subarctic, Nature, 331, 341–343, 1988. Martin, J. H., Gordon, R. M., and Fitzwater, S. E.: Iron in Antarctic waters, Nature, 345, 156–158, 1990. McKnight, D. M., Feder, G. L., and Stiles, E. A.: Effects on a blue-green alga of leachates of ash from the May 18 eruption, in: The 1980 Eruptions of Mount St. Helens, edited by: Lipman, P. W. and Mullineaux, D. R., USGS Professional Paper, Washington, 733–741, 1971. McKnight, D. M., Feder, G. L., and Stiles, E. A.: Toxicity of volcanic-ash leachate to a blue-green alga: results of a preliminary bioassay experiment, Environ. Sci. Technol., 15, 362–364, 1981. Mendez, J., Guieu, C., and Adkins, J.: Atmospheric input of manganese and iron to the ocean: Seawater dissolution experiments with Saharan and North American dusts, Mar. Chem., in press, 2010. Middleton, G. V., Church, M. J., and Coniglio, M.: Encyclopedia of Sediments and Sedimentary Rocks, Springer, Boston, 2003. Mills, M. M., Ridame, C., Davey, M., La Roche, J., and Geider, R.: Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic, Nature, 429, 292–294, 2004. Morel, F. M. M., Milligan, A. J., and Saito, M. A.: Marine bioinorganic chemistry: The role of trace metals in the oceanic cycles of major nutrients, in: The Oceans and Marine Geochemistry, edited by: Elderfield, H., Treatise on Geochemistry, Elsevier Pergamon, Amsterdam-Boston-Heidelberg-London-New York-Oxford-Paris-San Diego-San Francisco-Singapore-Sydney-Tokyo, 113–143, 2004. Nehring, N. L. and Johnston, D. A.: Use of ash leachates to monitor gas emissions, in: The 1980 Eruptions of Mount St. Helens, edited by: Lipman, P. W., and Mullineaux, D. R., USGS Professional Paper, Washington, 251–254, 1981. Nemani, R. R., Keeling, C. D., Hashimoto, H., Jolly, W. M., Piper, S. C., Tucker, C. J., Myneni, R. B., and Running, S. W.: Climate-driven increases in global terrestrial net primary production from 1982–1999, Science, 300, 1560–1563, 2003. Newcomb, T. W. and Flagg, T. A.: Some Effects of Mt. St. Helens Volcanic Ash on Juvenile Samlon Smolts, Mar. Fish. Rev., 45, 8–12, 1983. Nielsen, S. H. H., Hodell, D. A., Kamenov, G., Guilderson, T., and Perfit, M. R.: Origin and significance of ice-rafted detritus in the Atlantic sector of the Southern Ocean, Geochem. Geophy. Geosy., 8, 1–23, 2007. Niemeier, U., Timmreck, C., Graf, H.-F., Kinne, S., Rast, S., and Self, S.: Initial fate of fine ash and sulfur from large volcanic eruptions, Atmos. Chem. Phys., 9, 9043–9057, 2009. Olgun, N., Duggen, S., Croot, P. L., Delmelle, P., Dietze, H., Schacht, U., Óskarsson, N., Siebe, C., and Auer, A.: Surface ocean iron fertilization: The role of airborne volcanic ash from subduction zone and hotspot volcanoes and related fluxes into the Pacific Ocean, Global Biogeochem. Cy., in review, 2010. Oppenheimer, C.: Limited global change due to the largest known Quaternary eruption, Toba 74 kyr BP?, Quaternary Sci. Rev., 21, 1593–1609, 2002. Oppenheimer, C.: Volcanic Degassing, in: The Crust, edited by: Rudnick, R. L., Treatise on Geochemistry, Elsevier Pergamon, Amsterdam-Boston-Heidelberg-London-New York-Oxford-Paris-San Diego-San Francisco-Singapore-Sydney-Tokyo, 123–166, 2004. Óskarsson, N.: The interaction between volcanic gases and tephra: Flourine adhering to tephra of the 1970 Hekla eruption, J. Volcanol. Geoth. Res., 8, 251–266, 1980. Óskarsson, N.: The chemistry of Icelandic lava incrustations and the latest stages of degassing, J. Volcanol. Geoth. Res., 10, 93–111, 1981. Parekh, P., Follows, M. J., and Boyle, E. A.: Decoupling of iron and phosphate in the global ocean, Global Biogeochem. Cy., 19, 1–16, 2005. Pedersen, G. K., and Surlyk, F.: Dish structures in Eocene volcanic ash layers, Denmark, Sedimentology, 24, 581–590, 1977. Randazzo, L. A., Censi, P., Saiano, F., Zuddas, P., Aricò, P., and Mazzola, S.: Trace elements release from volcanic ash to seawater. Natural concentrations in Central Mediterraenan Sea, European Geosciences Union Meeting, Vienna, 2009, Rea, D. K., Scholl, D. W., and Allan, J. F.: Proceedings of the Ocean Drilling Program 145, Scientific Results, 1995. Rolett, B. and Diamond, J.: Environmental predictors of pre-European deforestation on Pacific islands, Nature, 431, 443–446, 2004. Rose, W. I.: Scavenging of volcanic aerosol by ash: atmospheric and volcanologic implications, Geology, 5, 621–624, 1977. Rubin, C. H., Noji, E. K., Seligman, P. J., Holtz, J. L., Grande, J., and Vittani, F.: Evaluating a flourosis hazard after a volcanic eruption, Arch. Environ. Health, 49, 395–401, 1994. Sansone, F. J., Benitez-Nielson, C. R., DeCarlo, E. H., Resing, J. A., Vink, S. M., Heath, J. A., and Huebert, B. J.: Geochemistry of atmospheric aerosols generated from lava-seawater interactions, Geophys. Res. Lett., 29, 1–4, 2002. Sarmiento, J. L.: Atmospheric CO₂ stalled, Nature, 365, 697–698, 1993. Schmincke, H.-U.: Volcanism, Springer-Verlag, Berlin Heidelberg New York, 324~pp., 2004. Sigurdsson, H., Houghton, B., McNutt, S. R., Rymer, H., and Stix, J.: Encyclopedia of Volcanoes, Academic Press, San Diego California, 2000. Smith, D. B., Zielinski, R. A., and Rose, W. I.: Leachability of uranium and other elements from freshly erupted volcanic ash, J. Volcanol. Geoth. Res., 13, 1–30, 1982. Smith, D. B., Zielinski, R. A., Taylor, H. E., and Sawyer, M. B.: Leaching Characteristics of Ash from the May 18, 1980, Eruption of Mount St. Helens Volcano, Washington, Bulletin of Volcanology, 46, 103–124, 1983. Smith, M. A. and White, M.: Observations on lakes near Mount St. Helens: Phytoplankton, J. Arch. Hydrobiol., 104, 345–363, 1985. Spirakis, C. S.: Iron fertilization with volcanic ash?, Eos Trans. AGU, 72(47), 525–526, 1991. Straub, S. M. and Schmincke, H.-U.: Evaluating the tephra input into Pacific Ocean sediments: distribution in space and time, Geol. Rundsch., 87, 461–476, 1998. Symonds, R. B., Rose, W. I., Reed, M. H., Lichte, F. E., and Finnegan, D. L.: Volatilization, transport and sublimation of metallic and non-metallic elements in high temperature gases at Merapi Volcano, Indonesia, Geochim. Cosmochim. Acta, 51, 2083–2101, 1987. Taylor, H. E. and Lichte, F. E.: Chemical composition of Mount St. Helens volcanic ash, Geophys. Res. Lett., 7, 949–952, 1980. Textor, C., Graf, H. F., Herzog, M., Oberhuber, J. M., Rose, W. I., and Ernst, G. G. J.: Volcanic particle aggregation in explosive eruption columns. Part I: Parameterization of the microphysics of hydrometeors and ash, J. Volcanol. Geoth. Res., 150, 359–377, 2006. Uematsu, M., Toratani, M. M. K., Narita, Y., Senga, Y., and Kimoto, T.: Enhancement of primary productivity in the western North Pacific caused by the eruption of the Miyake-jima volcano, Geophys. Res. Lett., 31, 1–4, 2004. Walker, G. P. L. and Croasdale, R.: Characteristics of some basaltic pyroclastics, Bull. Volcanol., 35, 303–317, 1972. Watson, A. J.: Volcanic Fe, CO₂, ocean productivity and climate, Nature, 385, 587–588, 1997. Wells, M. L.: The level of iron enrichment required to initiate diatom blooms in HNLC waters, Mar. Chem., 82, 101–114, 2003. Wiesner, M. G., Wetzel, A., Catane, S. G., Listanco, E. L., and Mirabueno, H. T.: Grain size, areal thickness distribution and controls on sedimentation of the 1991 Mount Pinatubo tephra layer in the South China Sea, Bull. Volcanol., 66, 226–242, 2004. Witham, C. S., Oppenheimer, C., and Horwell, C. J.: Volcanic ash-leachates: a review and recommendations for sampling methods, J. Volcanol. Geoth. Res., 141, 299–326, 2005. Wolff-Boenisch, D., Gislason, S. R., and Oelkers, E. H.: The effect of fluoride on the dissolution rates of natural glasses at pH 4 and 25 °C, Geochim. Cosmochim. Acta, 68, 4571–4582, 2004a. Wolff-Boenisch, D., Gislason, S. R., Oelkers, E. H., and Putnis, C. V.: The dissolution rates of natural glasses as a function of their composition at pH 4 and 10.6, and temperatures from 25 to 74 °C, Geochim. Cosmochim. Acta, 68, 4843–4858, 2004b.