glacial-scale enrichment would result in an air-to-sea flux of about 4.6 mol C m⫺2year⫺1orabout 2 Pg C year⫺1over an oceanic area of3.6 ⫻ 107km2(50°S to 65°S). Seasonal icecover may reduce this estimate by a factor of 2.These estimates are several times larger thanthe present net annual Southern Ocean (south of50°S) uptake of CO2of 0.4 Pg C year⫺1(1) andcomparable to the current global ocean net up-take of atmospheric CO2. Dilution-correctedestimates of POC export (Table 1) extrapolatedto an annual basis suggests a similar flux on theorder of 8 mol C m⫺2year⫺1.These results demonstrate that iron additionto the Southern Ocean increases primary pro-ductivity and decreases pCO2. It remainsdifficult to extrapolate these findings with con-fidence to their impact on atmospheric compo-sition because the large-scale impacts of ironenrichment on midwater processes and thelength scales of POC remineralization are notyet known. The results strongly suggest, how-ever, that the Southern Ocean was more pro-ductive and exported more carbon during peri-ods of higher atmospheric iron input, whichoccurred during the last glacial maximum.References and Notes1. T. Takahashi et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 49, 1601 (2002).2. K. L. Daly et al., J. Geophys. Res. 106, 7107 (2001).3. D. M. Sigman, E. A. Boyle, Nature 407, 859 (2000).4. K. S. Johnson et al., Mar. Chem. 57, 137 (1997).5. S. E. Fitzwater et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 47, 3159 (2000).6. P. W. Boyd et al., Nature 407, 695 (2000).7. F. Gervais et al., Limnol. Oceanogr. 47, 1324 (2002).8. J. H. Martin, Paleoceanography 5, 1 (1990).9. D. Archer et al., Rev. Geophys. 38, 159 (2000).10. J. K. Moore et al., Global Biogeochem. Cycles 14, 455(2000).11. A. J. Watson et al., Nature 407, 730 (2000).12. R. F. Anderson, Z. Chase, M. Q. Fleisher, J. Sachs, Deep-Sea Res. Part II Top. Stud. Oceanogr. 49, 1909 (2002).13. J. R. Petit et al., Nature 399, 429 (1999).14. R. A. Armstrong et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 49, 2265 (2002).15. K. H. Coale et al., Nature 383, 495 (1996).16. A. Tsuda et al., Science 300, 958 (2003).17. R. Schlitzer, EOS 81, 45 (2000).18. M. R. Hiscock et al., Deep-Sea Res. II 50, 533 (2003).19. T. Trull et al., Deep-Sea Res. Part II Top. Stud. Oceanogr.48, 2439 (2001).20. K. H. Coale et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 45, 919 (1998).21. Iron enrichments were conducted by R/V Revelle. Thenorthern patch was deployed 10 to 12 January 2002 at56.23°S and 172°W by injecting 631 kg of iron (as acidiciron sulfate dissolved in seawater) into the ship’s wake andspread over an area of 225 km2. Iron infusions in the northpatch of 631 kg and 450 kg were repeated on 16 Januaryand 10 February, respectively. The southern patch wasdeployed 24 to 26 January at 66.45°S and 171.8°W, withrepeated infusions on 29 January, 1 February, and 5 Feb-ruary. Each infusion involved 315 kg spread over a 225 km2area. For both patches, initial iron infusions were supple-mented with infusions of SF6and3He as inert chemicaltracers. This allowed for rapid detection of the infused areaand provided estimates of mixing and gas exchange withthe atmosphere. Lagrangian drifter buoys were deployedboth inside and outside the enriched areas.22. K. H. Coale, X. Wang, S. J. Tanner, K. S. Johnson, Deep-Sea Res. Part II Top. Stud. Oceanogr. 50, 635 (2003).23. K. Johnson et al., EOS 83 (suppl.), F799 (2002).24. E. R. Abraham et al., Nature 407, 727 (2000).25. P. G. Falkowski, J. A. Raven, Aquatic Photosynthesis(Blackwell Scientific, Malden, MA, 1997).26. M. Behrenfeld et al., Nature 371, 508 (1996).27. Z. Kolber et al., Nature 371, 145 (1994).28. P. W. Boyd, E. R. Abraham, Deep-Sea Res. Part II Top.Stud. Oceanogr. 48, 2529 (2001).29. P. W. Boyd, Deep-Sea Res. Part II Top. Stud. Ocean-ogr. 49, 1803 (2002).30. M. R. Landry, R. P. Hassett, Mar. Biol. 67, 283 (1982).31. M. P. Gall, R. Strzepet, M. Maldonado, P. W. Boyd, Deep-SeaRes. Part II Top. Stud. Oceanogr. 48, 2571 (2001).32. M. R. Landry et al., Mar. Ecol. Prog. Ser. 201, 57 (2000).33. B. S. Twining et al., Anal. Chem. 75, 3806 (2003).34. S. Takeda, Nature 393, 774 (1998).35. M. A. Brzezinski et al., Mar. Ecol. Prog. Ser. 167, 89 (1998).36. M. T. Maldonado, N. M. Price, Mar. Ecol. Prog. Ser.141, 161 (1996).37. K. R. Timmermans et al., Mar. Ecol. Prog. Ser. 166,27(1998).38. W. P. Cochlan, D. A. Bronk, K. H. Coale, Deep-Sea Res.Part II Top. Stud. Oceanogr. 49, 3365 (2002).39. D. A. Hutchins, K. W. Bruland, Nature 393, 561 (1998).40. M. A. Brzezinski, D. R. Phillips, Limnol. Oceanogr. 42,856 (1997).41. R. R. Bidigare et al., EOS 83 (suppl.), F798 (2002).42. K. O. Buesseler et al., Science 304, 414 (2004).43. J. K. B. Bishop et al., Science 304, 417 (2004).44. C. Sweeney et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 47, 3395 (2000).45. B. Hales, T. Takahashi, J. Atmos. Ocean. Technol. 19,1096 (2002).46. W. O. Smith et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 47, 3073 (2000).47. S. Levitus, U.S. World Ocean Atlas (U.S. Departmentof Commerce, 1998).48. R. J. Olson et al., Deep-Sea Res. Part II Top. Stud.Oceanogr. 47, 3181 (2000).49. V. M. Franck et al., Deep-Sea Res. Part II Top. Stud. Ocean-ogr. 47, 3315 (2000).50. We wish to thank the entire SOFeX group, crew, andofficers of RV Revelle,RVMelville, and U.S. CoastGuard Research Ice Breaker Polar Star and two verythorough reviewers. This research was supported bygrants from NSF, Chemical and Biological Oceanog-raphy, and U.S. Department of Energy, Office ofScience, Biological and Environmental Research.Supporting Online Materialwww.sciencemag.org/cgi/content/full/304/5669/408/DC1Materials and MethodsFigs. S1 to S5Tables S1 and S2References29 July 2003; accepted 25 March 2004REPORTSThe Effects of Iron Fertilizationon Carbon Sequestration in theSouthern OceanKen O. Buesseler,* John E. Andrews,Steven M. Pike, Matthew A. CharetteAn unresolved issue in ocean and climate sciences is whether changes to the surfaceocean input of the micronutrient iron can alter the flux of carbon to the deep ocean.During the Southern Ocean Iron Experiment, we measured an increase in the flux ofparticulate carbon from the surface mixed layer, as well as changes in particle cyclingbelow the iron-fertilized patch. The flux of carbon was similar in magnitude to thatof natural blooms in the Southern Ocean and thus small relative to globalcarbon budgets and proposed geoengineering plans to sequester