Concluding remarks

The decision to carry out large-scale OIF should be based on a comprehensive assessment of the long- and short-term as well as local and global effects derived from experiments and models, hence taken by an international body, preferably an agency of the UN specifically established for the purpose. This science-oriented body would subsequently manage and monitor larger scale OIF whether carried out by itself (analogous to deployment of experts by the well-known International Atomic Energy Agency, IAEA, of the UN) or by private companies under contract. OIF can be opened to the carbon credit market only if such an independent body allots a specific carbon quota per tonne of iron added in a specific season and region. For reasons dealt with below, inherent uncertainties are likely to prevent the scientific community from ever being in a position to allot fixed quotas for the SO. Indeed, we feel it is highly unlikely that a free-for-all carbon market could ever take over the SO as feared by many scientists (Chisholm et al. 2001) owing to the verification problem. It is up to the scientific community to exercise tight control over any large-scale OIF operation by generating the knowledge required to assess its effects. Statements calling for more experiments have been made by several scientific and other international bodies (Buesseler et al. 2008).

We have outlined hypothetical differences between open ACC and land-influenced waters above; another region where a very different type of phyto-plankton assemblage is present is the silicon-limited band of the ACC north of the Polar Front, in particular the regions where Antarctic Intermediate Water is formed. The SOFEX north patch, carried out in low-silicon waters, induced a bloom of thin-shelled pennate diatoms followed by significant enhancement of vertical flux (Bishop et al. 2004; Coale et al. 2004). However, in addition to thin-shelled diatoms, haptophyte flagellates known to produce copious quantities of DMSP, in particular the colonial species Phaeocystis and the calcifying coccol-ithophorids, also dominate the phytoplankton of this region (Seeyave et al. 2007; Lampitt et al. 2008). If OIF stimulates growth of coccolithophorids then pCO2 decrease caused by the uptake and export of organic carbon will be offset by the increase resulting from CaCO3 formation that reduces the alkalinity as well as the pH of seawater.

Experiments in this area would shed light on the much debated factors selecting for diatom or haptophyte dominance of the SO phytoplankton blooms (Smetacek et al. 2004). Thus, Phaeocystis blooms are recurrent in the Ross Sea but not in the Atlantic Sector and it is possible that sustained fertilization may lead to sustained blooming of this species, which does not appear to either provide high-quality food to zooplankton or contribute as efficiently to vertical flux as do diatoms. The toxic algal blooms reported from coastal waters around the world are unlikely to occur in the SO, although it cannot be excluded that toxic species of diatoms (Pseudo-nitzschia spp.), not currently present, may appear in the future. These possibilities underline the need to first carry out experiments but also, if they prove successful, to monitor carefully the effects of any large-scale OIF continuously and stop fertilization if and when needed.

Prolonged OIF will certainly boost zooplankton stocks, in particular copepods, and possibly also their predator populations. Surface-living, copepod-feeding fish are absent in the HNLC ACC (Smetacek et al. 2004), so it is impossible to predict which other predator groups, from coelenterates (jelly-fish) and amphipods, to mesopelagic fish and squid and even the copepod-feeding, endangered southern right whales, might profit from copepod population build-up. It will also be necessary to follow the effects of sustained fertilization on the mesopelagic community of copepods and radiolarians because, if their population density increases over time, they will intercept an increasingly larger proportion of the deep sinking flux. In such a case, it would be advisable to interrupt OIF for appropriate periods. It would also be necessary to monitor closely oxygen concentrations in the water column and sediments underlying OIF regions and halt operations if and when large oxygen depletion begins to take place.

Even under the best possible conditions, OIF will have only a limited effect on the rate at which atmospheric CO2 is projected to rise, but the amount involved is too large to be discounted; in short, we cannot afford not to thoroughly investigate the potential of this technique. A further benefit accruing from large-scale experiments is the attention they draw from the media, eager to report new developments in the global struggle, now in its infancy, that will help meet the challenge of global warming. The case for and against OIF can be used as a platform to educate the public on the workings of the global carbon cycle and the anthropogenic impact on it by providing a perspective on the quantities involved. OIF experiments would also serve as an ideal training ground for the next generation of ocean scientists faced with the challenge of coping with ongoing climate change in a global context.

References

Abelmann, A., Gersonde, R., Cortese, G., Kuhn, G. & Smetacek, V. 2006 Extensive phytoplankton blooms in the Atlantic Sector of the glacial Southern Ocean. Paleoceanography 21, PA1013. (doi:10.1029/2005PA001199) Anderson, R. F., Chase, Z., Fleisher, M. Q. & Sachs, J. 2002 The Southern Ocean's biological pump during the last glacial maximum. Deep Sea Res. II49, 9-10. (doi:10.1016/S0967-0645(02)00018-8) Assmy, P., Henjes, J., Klaas, C. & Smetacek, V. 2007 Mechanisms determining species dominance in a phytoplankton bloom induced by the iron fertilisation experiment EisenEx in the Southern Ocean. Deep Sea Res. 154, 340-362. (doi:10.1016/j.dsr.2006.12.005) Atkinson, A., Siegel, V., Pakhomov, E. A. & Rothery, P. 2004 Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432, 100-103. (doi:10.1038/nature02996) Bakun, A. & Weeks, S.J. 2004 Greenhouse gas buildup, sardines, submarine eruptions and the possibility of abrupt degradation of intense marine upwelling ecosystems. Ecol. Lett. 7, 1015-1023. (doi:10.1111/j.1461-0248.2004.00665.x) Bathmann, U. V., Scharek, R., Klaas, C., Dubischar, C. D. & Smetacek, V. 1997 Spring development of phytoplankton biomass and composition in major water masses of the Atlantic sector of the Southern Ocean. Deep Sea Res. II44, 51-67. Beaulieu, S. E. 2002 Accumulation and fate of phytodetritus on the sea floor. In

Oceanography and Marine Biology: An Annual Review, eds. Gibson, R. N., Barnes, M. & Atkinson, R. J. London: Taylor and Francis, pp. 171-232. Bishop, J. K. B., Wood, T. J., Davis, R. E. & Sherman, J. T. 2004 Robotic observations of enhanced carbon biomass and export at 55 degrees S during SOFeX. Science 304, 417-420. (doi:10.1126/science.1087717) Blain, S. et al. 2007 Effect of natural iron fertilization on carbon sequestration in the

Southern Ocean. Nature 446, 1070-1074. (doi:10.1038/nature05700) Boyd, P. et al. 2000 Phytoplankton bloom upon mesoscale iron fertilisation of polar

Southern Ocean waters. Nature 407, 695-702. (doi:10.1038/35037500) Boyd, P. W. et al. 2007 Mesoscale iron enrichment experiments 1993-2005: synthesis and future directions. Science 315, 612-617. (doi:10.1126/science.1131669) Boyle, E. A. 1988 Vertical oceanic nutrient fractionation and glacial-interglacial CO2

cycles. Nature 331, 55-56. (doi:10.1038/331055a0) Buesseler, K. O. & Boyd, P. W. 2003 Will ocean fertilization work? Science 300, 67-68.

(doi:10.1126/science.1082959) Buesseler, K. O. et al. 2008 Ocean iron fertilization: moving forward in a sea of uncertainty. Science 319, 162. (doi:10.1126/science.1154305) Cassar, N., Bender, M.L., Barnett, B. A., Songmiao, F., Moxim, W. J., Levy, H. II & Tilbrook, B. 2007 The Southern Ocean biological response to aeolian iron deposition. Science 317, 1067-1070. (doi:10.1126/science.1144602)

Chisholm, S. W. & Morel, F. M. M. 1991 What regulates phytoplankton production in nutrient-rich areas of the open sea? Limnol. Oceanogr. 36, U1507-U1511. Chisholm, S., Falkowski, P. & Cullen, J. 2001 Dis-crediting ocean fertilisation. Science

294, 309-310. (doi:10.1126/science.1065349) Cisewski, B., Strass, V. H. & Prandke, H. 2005 Upper-ocean vertical mixing in the Antarctic Polar Frontal Zone. Deep Sea Res. II52, 1087-1108. (doi:10.1016/j.dsr2.2005.01.010) Cisewski, B., Strass, V. H., Losch, M. & Prandke, H. 2008 Mixed layer analysis of a mesoscale eddy in the Antarctic Polar Front Zone. J. Geophys. Res. Ocean. 113, C05017. (doi:10.1029/2007JC004372) Coale, K. H. et al. 1996 A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the Equatorial Pacific Ocean. Nature 383, 495-501. (doi:10.1038/383495a0) Coale, K. H. et al. 2004 Southern Ocean iron enrichment experiment: carbon cycling in high-and low-Si waters. Science 304, 408-414. (doi:10.1126/science.1089778) Crutzen, P.J. 1991 Methane's sinks and sources. Nature 350, 380-381.

(doi:10.1038/350380a0) de Baar, H. J. W. et al. 2005 Synthesis of iron fertilization experiments: from the iron age in the age of enlightenment. J. Geophys. Res. 110, C09S16. (doi:10.1029/2004JC002601) Ducklow, H. W. & Harris, R. P. (eds.) 1993 JGOFS: The North Atlantic Bloom

Experiment. Deep Sea Res. II40, 1-461. Falkowski, P. G., Barber, R. T. & Smetacek, V. 1998 Biogeochemical controls and feedbacks on ocean primary production. Science 281, 200-206. (doi:10.1126/science.281.5374.200) Falkowski, P. et al. 2000 The global carbon cycle: a test of our knowledge of earth as a system. Science 290, 291-296. (doi:10.1126/science.290.5490.291) Frost, B. W. 1996 Phytoplankton bloom on iron rations. Nature 383, 475-476.

(doi:10.1038/383475a0) Fuhrman, J. A. & Capone, D. G. 1991 Possible biogeochemical consequences of ocean fertilization. Limnol. Oceanogr. 36, 1951-1959. Galbraith, E. D., Jaccard, S. L., Pedersen, T. F., Sigman, D. M., Haug, G. H., Cook, M., Southon, J. R. & Francois, R. 2007 Carbon dioxide release from the North Pacific abyss during the last deglaciation. Nature 449, 890-893. (doi:10.1038/nature06227) Gervais, F., Riebesell, U. & Gorbunov, M. Y. 2002 Changes in primary productivity and chlorophyll a in response to iron fertilization in the Southern Polar Frontal Zone. Limnol. Oceanogr. 47, 1324-1335. Gonzalez, H.E. 1992 The distribution and abundance of krill faecal material and oval pellets in the Scotia and Weddell Seas (Antarctica) and their role in particle flux. Polar Biol. 12, 81-91. (doi:10.1007/BF00239968) Gunson, J. R., Spall, S. A., Anderson, T. R., Jones, A., Totterdell, I. J. & Woodage, M. J. 2006 Climate sensitivity to ocean dimethylsulphide emissions. Geophys. Res. Lett. 33, L07701. (doi:10.1029/2005GL024982) Haberl, H., Erb, K. H., Krausman, F., Gaube, V., Bondeau, A., Plutzar, C., Gingrich, S., Lucht, W. & Fischer-Kowalski, M. 2007 Quantifying and mapping the human appropriation of net primary production in earth's terrestrial ecosystems. Proc. Natl Acad. Sci. USA 104, 12 942-12 947. (doi:10.1073/pnas.0704243104) Hamm, C. & Smetacek, V. 2007 Armor: why, when, and how. In Evolution of Primary Producers in the Sea, eds. Falkowski, P. G. & Knoll, A. H. London: Elsevier, pp. 311-332.

Hart, T. J. 1942 Phytoplankton periodicity in Antarctic surface waters. Discovery Reports 21, 261-356.

Henjes, J., Assmy, P., Klaas, C., Verity, P. & Smetacek, V. 2007 Response of microzooplankton (protists and small copepods) to an iron-induced phytoplankton bloom in the Southern Ocean (EisenEx). Deep Sea Res. 154, 363-384. (doi:10.1016/j.dsr.(2006):12.004) Jacquet, S. H. M., Savoye, N., Dehairs, F., Strass, V. H. & Cardinal, D. 2008 Mesopelagic carbon remineralization during the European iron fertilization experiment. Glob. Biogeochem. Cycle. 22, GB1023. (doi:10.1029/2006GB002902) Jansen, S., Klaas, C., Kragefsky, S., von Harbou, L. & Bathmann, U. 2006 Reproductive response of the copepod Rhincalanus gigas to an iron-induced phytoplankton bloom in the Southern Ocean. Polar Biol. 29, 1039-1044. (doi:10.1007/s00300-006-0147-0) Jayakumar, D. A., Naqvi, S. W. A., Narvekar, P. V. & George, M. D. 2001 Methane in coastal and offshore waters of the Arabian Sea. Mar. Chem. 74, 1-13. (doi:10.1016/S0304-4203(00)00089-X) Jickells, T.D. et al. 2005 Global iron connections between desert dust, ocean biogeochemistry, and climate. Science 308, 67-71. (doi:10.1126/science.1105959) Jin, X. & Gruber, N. 2003 Offsetting the radiative benefit of ocean iron fertilisation by enhancing N2O emissions. Geophys. Res. Lett. 30, 2249. (doi:10.1029/2003GL018458) Kallel, N., Labeyrie, L. D., Juillet-Leclerc, A. & Duplessy, J. C. 1988 A deep hydrological front between intermediate and deep-water masses in the glacial Indian Ocean. Nature 333, 651-655. (doi:10.1038/333651a0) Landry, M. R. & Hassett, R. P. 1982 Estimating the grazing impact of marine micro-zooplankton. Mar. Biol. 67, 283-288. (doi:10.1007/BF00397668) Law, C. S. & Ling, R.D. 2001 Nitrous oxide flux and response to increased iron availability in the Antarctic Circumpolar Current. Deep Sea Res. II48, 2509-2527. (doi:10.1016/S0967-0645(01)00006-6) Lawrence, M. G. 2002 Side effects of oceanic iron fertilization. Science 297, 1993.

(doi:10.1126/science.297.5589.1993b) Laws, R. W. 1977 Seals and whales of the Southern Ocean. Phil. Trans. R. Soc. B 279,

81-96. (doi:10.1098/rstb. 1977.0073) Le Quere, C. et al. 2007 Saturation of the Southern Ocean CO2 sink due to recent climate change. Science 316, 1735-1738. (doi:10.1126/science.1136188) Liss, P. S. 2007 Trace gas emissions from the marine biosphere. Phil. Trans. R. Soc. A

365, 1697-1704. (doi:10.1098/rsta.2007.2039) Losch, M., Schukay, R., Strass, V. & Cisewski, B. 2006 Comparison of a NLOM data assimilation product to direct measurements in the Antarctic Polar Frontal Zone: a case study. Ann. Geophys. 24, 3-6. Maier-Reimer, E., Mikolajewicz, U. & Winguth, A. 1996 Future ocean uptake of CO2: interaction between ocean circulation and biology. Climate Dyn. 12, 711-721. (doi:10.1007/s003820050138) Martin, J. H. 1990 Glacial-interglacial CO2 change: the iron hypothesis.

Paleoceanography 5, 1-13. (doi:10.1029/PA005i001p00001) Martin, J. H. & Fitzwater, S. E. 1988 Iron deficiency limits phytoplankton growth in the northeast Pacific subarctic. Nature 331, 341-343. (doi:10.1038/331341a0) Martin, J. H., Knauer, G. A., Karl, D. M. & Broenkow, W. W. 1987 Carbon cycling in the northeast Pacific. Deep Sea Res. A 34, 267-285. (doi:10.1016/0198-0149(87)90086-0) Martin, J. H. et al. 1994 Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean. Nature 371, 123-129. (doi:10.1038/371123a0)

Nevison, C.D., Lueker, T.J. & Weiss, R.F. 2004 Quantifying the nitrous oxide source from coastal upwelling. Glob. Biogeochem. Cycle 18, GB1018. (doi:10.1029/2003GB002110) Petit, J. R. et al. 1999 Climate and atmospheric history of the past 420 000 years from the

Vostok ice core, Antarctica. Nature 399, 429-436. (doi:10.1038/20859) Pollard, R., Sanders, R., Lucas, M. & Statham, P. 2007 The Crozet natural iron bloom and export experiment (CROZEX). Deep Sea Res. II54, 1905-1914. (doi:10.1016/j.dsr2.2007.07.023) Poulton, A. J., Mark Moore, C., Seeyave, S., Lucas, M. I., Fielding, S. & Ward, P. 2007 Phytoplankton community composition around the Crozet Plateau, with emphasis on diatoms and Phaeocystis. Deep Sea Res. II54, 2085-2105. (doi:10.1016/j.dsr2.2007.06.005) Salter, I., Lampitt, R. S., Sanders, R., Poulton, A., Kemp, A. E. S., Boorman, B., Saw, K. & Pearce, R. 2007 Estimating carbon, silica and diatom export from a naturally fertilised phytoplankton bloom in the Southern Ocean using PELAGRA: a novel drifting sediment trap. Deep Sea Res. II54, 2233-2259. (doi:10.1016/j.dsr2.2007.06.008) Sarmiento, J.L. & Orr, J. C. 1991 Three-dimensional simulations of the impact of Southern Ocean nutrient depletion on atmospheric CO2 and ocean chemistry. Limnol. Oceanogr. 36, 1928-1950. Seeyave, S., Lucas, M. I., Moore, C.M. & Poulton, A.J. 2007 Phytoplankton productivity and community structure in the vicinity of the Crozet Plateau during austral summer 2004/2005. Deep Sea Res. II54, 2020-2044. (doi:10.1016/j.dsr2.2007.06.010) Siegenthaler, U. et al. 2005 Stable carbon cycle-climate relationship during the late

Pleistocene. Science 310, 1313-1317. (doi:10.1126/science.1120130) Smetacek, V. 1985 Role of sinking in diatom life-history cycles: ecological, evolutionary and geological significance. Mar. Biol. 84, 239-251. (doi:10.1007/BF00392493) Smetacek, V. 1999 Diatoms and the ocean carbon cycle. Protist 150, 25-32. Smetacek, V. 2002 The ocean's veil. Nature 419, 565. (doi:10.1038/419565a) Smetacek, V. 2007 ?Es el declive del krill antartico resultado del calentamiento global o del exterminio de las ballenas? In Impactos del calentamiento global sobre los ecosistemas polares, ed. Duarte, C.M. Bilbao, Spain: Fundacion BBVA, pp. 45-81.

Smetacek, V. & Nicol, S. 2005 Polar ocean ecosystems in a changing world. Nature 437,

362-368. (doi:10.1038/nature04161) Smetacek, V. & Passow, U. 1990 Spring bloom initiation and Sverdrup's critical-depth model. Limnol. Oceanogr. 35, 228-234. Smetacek, V., Scharek, R. & Nothig, E.-M. 1990 Seasonal and regional variation in the pelagial and its relationship to the life history cycle of krill. In Antarctic Ecosystems, eds. Kerry, K. & Hempel, G. Heidelberg, Germany: Springer, pp. 103-116.

Smetacek, V., Assmy, P. & Henjes, J. 2004 The role of grazing in structuring Southern Ocean pelagic ecosystems and biogeochemical cycles. Antarctic Science 16, 541-558. (doi:10.1017/S0954102004002317) Spahni, R. et al. 2005 Atmospheric methane and nitrous oxide of the late Pleistocene from

Antarctic ice cores. Science 310, 1317-1321. (doi:10.1126/science.1120132) Stramma, L., Johnson, G. C., Sprintall, J. & Mohrholz, V. 2008 Expanding oxygen-minimum zones in the tropical oceans. Science 320, 655-658. (doi:10.1126/science.1153847) Strzepek, R. F. & Harrison, P. J. 2004 Photosynthetic architecture differs in coastal and oceanic diatoms. Nature 431, 689-692. (doi:10.1038/nature02954)

Suzuki, K., Saito, H., Hinuma, A., Kiyosawa, H., Kuwata, A., Kawanobe, K., Saino, T. & Tsuda, A. 2006 Comparison of community structure and photosynthetic physiology of phytoplankton in two mesoscale iron enrichment experiments in the NW subarctic Pacific. In Proc. PICES-IFEP Workshop on In Situ Iron Enrichment Experiments in the Eastern and Western Subarctic Pacific. Tovar-Sanchez, A., Duarte, C. M., Hernández-León, S. & Sanudo-Wilhelmy, S. A. 2007 Krill as a central node for iron cycling in the Southern Ocean. Geophys. Res. Lett. 34, L11601. (doi:10.1029/2006GL029096) Tsuda, A. et al. 2003 A mesoscale iron enrichment in the western subarctic Pacific induces a large centric diatom bloom. Science 300, 958-961. (doi:10.1126/science.1082000) Tsuda, A., Saito, H. & Sastri, A. R. 2006 Meso-and microzooplankton responses in the iron-enrichment experiments in the subarctic North Pacific (SEEDS, SERIES and SEEDS-II). In Proc. PICES-IFEP Workshop on In Situ Iron Enrichment Experiments in the Eastern and Western Subarctic Pacific. Turner, D. & Owens, N. J. P. 1995 A biogeochemical study in the Bellingshausen Sea: overview of the STERNA expedition. Deep-Sea Res. II42, 907-932. (doi:10.1016/0967-0645(95)00056-V) Turner, S. M., Harvey, M. J., Law, C. S., Nightingale, P. D. & Liss, P. S. 2004 Iron-induced changes in oceanic sulfur biogeochemistry. Geophys. Res. Lett. 31, L14307. (doi:10.1029/2004GL020296) Tyson, R. V. 1995 Sedimentary Organic Matter. London: Chapman and Hall. Walter, S., Peeken, I., Lochte, K., Webb, A. & Bange, H. W. 2005 Nitrous oxide measurements during EIFEX, the European Iron Fertilisation Experiment in the subpolar South Atlantic Ocean. Geophys. Res. Lett. 32, L23613. (doi:10.1029/2005GL024619) Wefer, G. 1989 Particle flux in the ocean: present and past. In Dahlem Conference, eds.

Berger, W. H., Smetacek, V. S. & Wefer, G. Chichester, UK: Wiley, pp. 139-154. Zeebe, R. E. & Archer, D. 2005 Feasibility of ocean fertilization and its impact on future atmospheric CO2 levels. Geophys. Res. Lett. 32, L09703. (doi:10.1029/2005GL022449)

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