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Contribution to the Theme Section ‘Implications of large-scale iron fertilization of the oceans’ Efficiency of carbon removal per added iron in ocean iron fertilization

Author(s): de Baar HJW, Gerringa LJA, Laan P, Timmermans KR

Published: July, 2008

Publisher: Marine Ecology Progress Series

DOI: 10.3354/meps07548

Tags: Ocean Fertilization

URL: http://www.int-res.com/abstracts/meps/v364/p269-282/

Abstract: The major response to ocean iron fertilization is by large diatoms, which at Fe-replete ambient seawater show an optimum C:Fe elemental ratio of ~23000 and a higher ratio of ~160000 or more under Fe-limited conditions. The efficiency of CO2 drawdown during the several weeks of artificial fertilization experiments with concomitant observations is in the range of 100 < (CO2:Fe) < 1000 and is unknown in direction (positive or negative) and magnitude in the period after observations. The efficiency of biogenic carbon export into deeper water layers ranges from ~650 < (C:Fe)export < ~25000 for reported export depths in the 100 to 250 m range. Variations in ocean initial conditions and variable weather during an experiment cause this range of ~2 orders of magnitude. Approximately 75% of Fe added in fertilization experiments is lost very rapidly. Hence the above efficiencies can be multiplied 4-fold, to ~2600 < (C:Fe)export < ~100000, for the sake of comparison with natural fertilization with Fe-organic complexes, which stabilize Fe in solution. Quantification of the Fe source of natural fertilization is difficult, leading to an export efficiency in the ~2400 < (C:Fe)export < ~800000 range. Due to severe under-sampling, the existing datasets of artificial experiments and natural fertilizations may allow a wider range of alternative assessments than reported here.


Ocean Iron Fertilization--Moving Forward in a Sea of Uncertainty

Author(s): Buesseler KO, Doney SC, Karl DM, Boyd PW, Caldeira K, Chai F, Coale KH, de Baar HJW, Falkowski PG, Johnson KS, Lampitt RS, Michaels AF, Naqvi SWA, Smetacek V, Takeda S, Watson AJ

Published: January, 2008

Publisher: Science

DOI: 10.1126/science.1154305

Tags: Ocean fertilization, Research

URL: http://www.sciencemag.org/content/319/5860/162.short

Abstract: It is premature to sell carbon offsets from ocean iron fertilization unless research provides the scientific foundation to evaluate risks and benefits.


Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions

Author(s): Boyd PW, Jickells TD, Law CS, Blain S, Boyle EA, Buesseler KO, Coale KH, Cullen JJ, de Baar HJW, Follows M, Harvey M, Lancelot C, Levasseur M, Owens NPJ, Pollard RT, Rivkin RB, Sarmiento JL, Schoemann V, Smetacek V, Takeda S, Tsuda A, Turner SM, Watson AJ

Published: February, 2007

Publisher: Science

DOI: 10.1126/science.1131669

Tags: Ocean Fertilization, Research

URL: http://www.sciencemag.org/content/315/5812/612.abstract

Abstract: Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has radically changed. Mesoscale iron addition experiments (FeAXs) have unequivocally shown that iron supply limits production in one-third of the world ocean, where surface macronutrient concentrations are perennially high. The findings of these 12 FeAXs also reveal that iron supply exerts controls on the dynamics of plankton blooms, which in turn affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulfur and ultimately influence the Earth climate system. However, extrapolation of the key results of FeAXs to regional and seasonal scales in some cases is limited because of differing modes of iron supply in FeAXs and in the modern and paleo-oceans. New research directions include quantification of the coupling of oceanic iron and carbon biogeochemistry.


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