A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

By Philip W. Boyd, A. Watson, C. Law, E. Abraham, T. Trull, R. Murdoch, D. Bakker, A. Bowie, K. Buesseler, Hoe Chang and 25 more. Nature, 2000

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Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the ‘iron hypothesis’. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.

Subfields: Ecology, Oceanography

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Citations in the corpus

The spatial structure of Antarctic biodiversity (2014, background): “These patterns reflect partial release of phytoplankton populations from micronutrient (trace metal) limitation, specifically by iron (Martin et al. 1994, Boyd et al. 2000, Ducklow et al. 2003).”
Growth rates, half‐saturation constants, and silicate, nitrate, and phosphate depletion in relation to iron availability of four large, open‐ocean diatoms from the Southern Ocean (2004, methodology): “In our present study, the diatoms were cultured under realistic conditions, i.e., natural HNLC Southern Ocean water without significant changes in the chemical composition of the growth medium (Gerringa et al. 2000; Timmermans et al. 2001).”
Nutrient limitation of primary productivity in the Southeast Pacific (BIOSOPE cruise) (2007, result): “These results are in accordance with the patterns found in other HNLC waters (e.g. Boyd et al., 2000).”
Synergistic effects of iron and temperature on Antarctic phytoplankton and microzooplankton assemblages (2009, background): “Similar trends have also been observed in other Southern Ocean in situ fertilization experiments (Boyd et al., 2000) as well as in other Fe-limited ecosystems (Hutchins and Bruland, 1998). www.biogeosciences.net/6/3131/2009/ Biogeosciences, 6, 3131–47, 2009 3142 J. M. Rose et al.: Synergistic…”
Co-limitation by iron and light of Chaetoceros brevis, C. dichaeta and C. calcitrans (Bacillariophyceae) (2001, background): “…nutrient, low chlorophyll (HNLC) regions, for example, the Southern Ocean, since there is ample evidence for both iron limitation (de Baar et al. 1995, Timmermans et al. 1998, Boyd et al. 2000) and light limitation (Mitchell et al. 1991, Behrenfeld & Kolber 1999) of phytoplankton photosynthesis.”
Iron-mediated changes in phytoplankton photosynthetic competence during SOIREE (2001, methodology): “During the experiment a deep chlorophyll-amaximum (DCM) developed (or was advected into) the surrounding HNLC waters (Boyd et al., 2000).”