MEPS 364:269-282 (2008)  -  doi:10.3354/meps07548

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

Hein J. W. de Baar1,2,*, Loes J. A. Gerringa2, Patrick Laan2, Klaas R. Timmermans2

1Ocean Ecosystems, Centre for Evolution and Ecology Studies, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
2Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg (Texel), The Netherlands

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.


KEY WORDS: Iron · Fertilization · Ocean · Efficiency · Carbon · Export · Diatoms


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Cite this article as: de Baar HJW, Gerringa LJA, Laan P, Timmermans KR (2008) Efficiency of carbon removal per added iron in ocean iron fertilization. Mar Ecol Prog Ser 364:269-282

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