Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern Ocean

Baar, H. J. W. de; Jong, Jeroen de; Bakker, Dorothee C E; Löscher, Bettina M.; Veth, C.; Bathmann, U.; Smetacek, Victor

doi:10.1038/373412a0

Cited by 794 publications

(493 citation statements)

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“…Although the nutrient pools were not raised substantially above the ambient levels, nitrogen was provided as ammonia, whereas nitrate is-by farthe dominant form in the ambient waters, which may have had a positive effect on algal growth. Moreover, iron supply, which has been claimed to limit phytoplankton production in Antarctic waters (de Baar et al 1995), is relatively high in the coastal environment studied, which receives inputs of glacial materials transporting iron-rich volcanic ash derived from eruptions at near-by Depception Island. We propose that the evidence presented here points to light-limitation of the phytoplankton community in ambient waters as the factor responsible for its low biomass and production relative to the mesocosm.…”

Section: Discussionmentioning

confidence: 99%

“…Hypotheses to account for this paradox span the full spectrum of possible limiting factors, including limitation by resources (nutrients and iron, light) and consumer pressure (e.g. Holm-Hansen et al 1984, Minas & Minas 1992, de Baar et al 1995. In addition to possible limiting factors, the capacity of Antarctic phytoplankton to realise the potential primary production possible with the nutrients present is believed to be constrained by the low maximum intrinsic growth rates believed to be possible in cold waters (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Experimental induction of a large phytoplankton bloom in Antarctic coastal waters

Agustı́¹,

Duarte²

2000

Mar. Ecol. Prog. Ser.

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The experimental enclosure of an Antarctic planktonic community in a large (35 m 3 ) mesocosm moored in Johnson's Dock (62°39.576' S, 60°22.408' W, Livingston Island, Bransfield Sector, Antarctica) was followed by a large phytoplankton bloom. This bloom, dominated by the large diatom Thalassiosira antarctica, reached a biomass 1000-fold greater than in the ambient waters. The net growth rate of T. antarctica averaged 0.53 ± 0.17 d -1 , with maximum net growth rates close to 1.0 d -1 , exceeding the predicted maximal population growth rates by 60 to 200%. The gross primary production in the mesocosm (49 mmol C m -3 d -1 ) was about 30 times greater than the concurrent gross production in the ambient waters, while sedimentation losses removed only between 2.1 to 13% of the biomass d -1 and cell mortality was negligible. The bloom development led to a decline of dissolved inorganic nutrient concentrations to values several times lower than those in the ambient waters, indicating that the ambient nutrients were both available and sufficient to allow the development of the massive algal bloom observed. Light-limitation of the phytoplankton community was likely the factor responsible for the low biomass and production in ambient waters relative to the mesocosm, as indicated by: (1) limited water transparency of about 1 m, which increased up to 6 m as a result of the sedimentation of the glacial flour in the mesocosm; (2) dense pigment packaging (14.7 ± 3 pg chl a µm -3 ) inside the phytoplankton cells of the community in the ambient waters compared to much lower values (4.2 ± 0.8 pg chl a µm -3 ) in the mesocosm community; (3) a specific light absorption of the phytoplankton community in the ambient waters 10 times higher (average specific PAR absorption ± SE = 0.018 ± 0.0038 m -1 mg chl a -1 ) than in the mesocosm community (0.0087 ± 0.002 m -2 mg -1 chl a); and (4)

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental induction of a large phytoplankton bloom in Antarctic coastal waters

Agustı́¹,

Duarte²

2000

Mar. Ecol. Prog. Ser.

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“…In high latitude regions, potential effects of low iron availability must be considered in the context of seasonal changes in light availability associated with incident solar radiation and deep winter mixing (e.g., Mitchell et al, 1991). For the Southern Ocean, in particular, uncertainty about what combination of factors regulates primary production has important implications for predicting the overall effects of marine processes in global carbon cycling (de Baar et al, 1995;Sarmiento and Le Quere, 1996;Arrigo et al, 1999). The role of iron in limiting Southern Ocean phytoplankton has been investigated chiefly via iron enrichment experiments in which properties such as chlorophyll, biomass, or physiological parameters are measured over time in control and enriched samples.…”

Section: Introductionmentioning

confidence: 99%

Phytoplankton and iron limitation of photosynthetic efficiency in the Southern Ocean during late summer

Sosik

Olson

2002

Deep Sea Research Part I: Oceanographic Research Papers

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As part of two USJGOFS cruises, we investigated spatial variability in phytoplankton properties across the strong environmental gradient associated with the Antarctic Polar Frontal Zone during late austral summers of 1997 and 1998. Cell properties, including size and an index of pigment content as well as photosynthetic efficiency (as indicated by relative variable fluorescence), changed dramatically across this frontal region. A general trend toward reduced photosynthetic efficiency south of the Polar Front was correlated with low dissolved iron concentration and is consistent with physiological iron limitation in the phytoplankton. We detected no significant differences in photosynthetic efficiency among different size classes of the dominant pico-to nanophytoplankton, despite a systematic community level shift toward larger sized cells south of the Polar Front. In contrast to other cells, those classified as cryptophyte algae showed relatively high photosynthetic efficiency in low iron waters; however, this group was never found in high abundance. One group, all cells p2 mm, showed an unexpected increase in intracellular pigment content (based on single cell chlorophyll fluorescence measurements) south of the Polar Front where dissolved iron concentration and the cells' relative abundance were low. Overall, these results suggest that group-or size-specific differences in physiological status were not directly regulating community structure in the pico-to nanophytoplankton during the late summer season; other processes, such as differential grazing or sinking losses, must be important.

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“…Wells, 1995 . Among these regions are the Antarctic Ž Ocean de Baar et al, 1990Baar et al, , 1995Buma et al, 1991;Scharek et al, . Ž 1997, the Equatorial Pacific Ocean Martin, 1992 .…”

Section: Discussionmentioning

confidence: 99%

“…Ž The effects of iron additions on phytoplankton de Baar et al, 1990;Buma et al, 1991;Timmermans et al, 1994;Scharek et al, . 1997 , the distribution of iron and other trace ele-Ž ments in the water column Saager et al, 1989;Nolting et al, 1991;de Baar et al, 1995;Loscher eẗ . al., 1997 and the chemical speciation of iron in Ž seawater Gledhill and van den Berg, 1995; in press are central themes in our work.…”

Section: Introductionmentioning

confidence: 99%

Responses of marine phytoplankton in iron enrichment experiments in the northern North Sea and northeast Atlantic Ocean

et al. 1998

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Short-term iron enrichment experiments were carried out with samples collected in areas with different phytoplankton activity in the northern North Sea and northeast Atlantic Ocean in the summer of 1993. The research area was dominated by high numbers of pico-phytoplankton, up to 70,000 ml y1 . Maximum chlorophyll a concentrations varied from about 1.0 mg y1 Ž . l in a high-reflectance zone caused by loose coccoliths, remnants from a bloom of Emiliania huxleyi and about 3.5 mg l y1 in a zone in which the phytoplankton were growing, to about 0.5 mg l y1 in the northeast Atlantic Ocean. From the high-reflectance zone to the northeast Atlantic Ocean, nitrate concentrations increased from 0.5 mM to 6.0 mM. Concentrations of reactive iron in surface water showed an opposite trend and decreased from about 2.6 nM in the high-reflectance zone to -1.0 nM in the northeast Atlantic Ocean. In the research area, no signs of true iron deficiency were found, but iron enrichments in the high-reflectance zone, numerically dominated by Synechococcus sp., resulted in increased nitrate uptake. Ammonium uptake was hardly affected. Strong support for the effect of Fe on cell physiology is Ž . given by the increase in the f-ratio. Net growth rates of the phytoplankton changes in cell numbers over 24 h were almost unchanged. Phytoplankton collected from the northeast Atlantic Ocean, did not show changes in the nitrogen metabolism upon addition of iron. Net growth rates in these incubations were low or negative, with only slightly higher values with additional iron. q

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Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern Ocean

Cited by 794 publications

References 30 publications

Experimental induction of a large phytoplankton bloom in Antarctic coastal waters

Experimental induction of a large phytoplankton bloom in Antarctic coastal waters

Phytoplankton and iron limitation of photosynthetic efficiency in the Southern Ocean during late summer

Responses of marine phytoplankton in iron enrichment experiments in the northern North Sea and northeast Atlantic Ocean

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