Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean

Martin, John H.; Coale, Kenneth H.; Johnson, Kenneth S.; Fitzwater, Steve E.; Gordon, R. Michael; Tanner, Sara J.; Hunter, Craig N.; Elrod, Virginia A.; Nowicki, Jocelyn L.; Coley, Teresa L.; Barber, Richard T.; Lindley, Steven T.; Watson, Andrew; Scoy, K. Van; Law, C. S.; Liddicoat, M.I.; Ling, Roger; Stanton, Tim; Stockel, James A.; Collins, Curtis A.; Anderson, Alan H.; Bidigare, Robert R.; Ondrusek, Michael; Latasa, Mikel; Millero, Frank J.; Lee, Kitack; Yao, Wensheng; Zhang, Jiazhong; Friederich, Gernot; Sakamoto, Carole M.; Chávez, Francisco P.; Buck, Kristen N.; Kolber, Zbigniew; Greene, Richard M.; Falkowski, Paul G.; Chisholm, Sallie W.; Hoge, Frank E.; Swift, Robert N.; Yungel, James K.; Turner, Suzanne M.; Nightingale, Philip D.; Hatton, Angela D.; Liss, Peter S.; Tindale, Neil

doi:10.1038/371123a0

Cited by 1,248 publications

(718 citation statements)

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“…Addition of approximately 4 nM iron during IronEx I resulted in a threefold increase in chlorophyll a and productivity (Martin et al 1994). The response during IronEx II, in which three pulses of iron were added, was even greater.…”

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confidence: 83%

“…In contrast, halfsaturation constants for iron have been estimated as 34 to 120 pM, which is close to four times higher than the ambient dissolved iron concentration (Price et al 1994;Coale et al 1996a). Finally, during both the IronEx I and II experiments, NH concentrations were consistently lower inside the ϩFe ϩ 4 patch than outside, whereas chlorophyll and productivity increased (Martin et al 1994;W. Cochlan pers.…”

Section: Prochlorococcus Productivity-to Compare Changes Inmentioning

confidence: 99%

“…The iron hypothesis explains these observations by maintaining that phytoplankton productivity and biomass are limited by iron (Martin et al 1991;Coale et al 1996b). Indeed, ambient iron levels are low in high-nutrient low-chlorophyll (HNLC) areas (Martin et al 1991;Coale et al 1996b), and the addition of iron to incubation bottles has been shown to increase net growth rates, chlorophyll yields, nitrate uptake, and nutrient consumption, particularly of the larger cells Martin et al 1991;Price et al 1991Price et al , 1994Takeda and Obata 1995;Fitzwater et al 1996). The ecumenical hypothesis (Morel et al 1991b;Price et al 1994;Cullen 1995) and the recent synthesis of data from the equatorial Pacific by Landry et al (1997) extend this explanation by invoking both iron limitation and grazing to explain the HNLC regions.…”

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confidence: 99%

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Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific

Mann

Chisholm

2000

Limnology & Oceanography

117

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Prochlorococcus, a small unicellular cyanobacterium, is an important member of the phytoplankton community in the eastern equatorial Pacific. When these waters were enriched with iron during IronEx II, the chlorophyll per cell and cell size of Prochlorococcus increased, implying that they were iron limited. The extent of this limitation was unclear, however, and the number of Prochlorococcus remained constant. To examine whether cell division rates were stimulated significantly by iron, we used a cell cycle analysis approach to measure them in and out of the Fe-enriched patch and in Fe-enriched bottles. The cell division rate increased from 0.6 to 1.1 d Ϫ1 over 6 d of exposure to the elevated iron concentrations in the patch. Cells incubated in bottles with additional iron had rates of 1.4 d Ϫ1 or two doublings per day. Prochlorococcus mortality rates, measured independently, nearly doubled after the addition of iron. This matched the increase in the cell division rate and maintained a relatively constant population size. Thus the cell division rates of even the smallest phytoplankton in the equatorial Pacific are significantly iron limited, but biomass is constrained by both iron limitation and microzooplankton grazing. The differential response of individual phytoplankton groups to the addition of iron during IronEx II was at least partially a result of differential mortality rates over the time course of the experiment. How the community would respond to sustained fertilization, however, is not obvious.Nitrate and phosphate concentrations are persistently high in the euphotic zone of the equatorial Pacific, and phytoplankton biomass and productivity are lower than expected based on nutrient availability (Cullen 1991;Frost and Franzen 1992). The phytoplankton community is dominated by small picoplankton (Chavez 1989), which have a large surface area to volume ratio and are less likely to be diffusion limited by either nutrients or trace metals than larger cells (Morel et al. 1991a). Measured cell division rates are often 0.5 d Ϫ1 or higher, both for the phytoplankton community as a whole (Barber and Chavez 1991;Chavez et al. 1991;Cullen 1991;Cullen et al. 1992;Landry et al. 1995;Verity et al. 1996;Latasa et al. 1997;Lindley and Barber 1998) and for the small cyanobacterium Prochlorococcus (DuRand 1995;Landry et al. 1995;Vaulot et al. 1995;Binder et al. 1996;Latasa et al. 1997;Liu et al. 1997; Vaulot and Dom-1 Corresponding author (chisholm@mit.edu). AcknowledgementsWe thank the captain and crew of the RV Melville, as well as Kenneth Coale and the Moss Landing IronEx group, for making the experiment possible. We also thank R. Michael Gordon for iron concentration measurements, and Richard Barber, William Cochlan, Michael R. Landry, and Makoto Saito for sharing unpublished data. Comments by J. Cullen, P. Falkowski, and an anonymous reviewer helped improve the manuscript.

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confidence: 83%

Section: Prochlorococcus Productivity-to Compare Changes Inmentioning

confidence: 99%

mentioning

confidence: 99%

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Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific

Mann

Chisholm

2000

Limnology & Oceanography

117

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“…The first mesoscale iron enrichments in the Equatorial Pacific, IRONEX I and II (Coale et al, 1996;Martin et al, 1994), and in the Southern Ocean, SOIREE, (Boyd and Law, 2001), have answered in the affirmative by dramatic demonstration of intense phytoplankton growth after relief of iron limitation. However, there is still much to be learnt from iron enrichment experiments, notably insight into mechanisms of biogeochemical cycling of iron and other nutrients.…”

Section: Introductionmentioning

confidence: 95%

Spatial and temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment

et al. 2005

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Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. concentrations increased at the depth of the chlorophyll maximum when iron concentrations returned to pre-infusion concentrations (b80 pM) possibly due to biological production related to iron reductase activity.In this work, Fe(II) and dissolved iron were used as tracers themselves for subsequent iron infusions when no further SF 6 was added. EisenEx was subject to periods of weak and strong mixing. Slow mixing after the second infusion allowed significant concentrations of Fe(II) and Fe to exist for several days. During this time, dissolved and total iron in the infusion plume behaved almost conservatively as it was trapped between a relict mixed layer and a new rain-induced mixed layer. Using dissolved iron, a value for the vertical diffusion coefficient K z =6.7F0.7 cm 2 s À1 was obtained for this 2-day period. During a subsequent surface survey of the iron-enriched patch, elevated levels of Fe(II) were found in surface waters presumably from Fe(II) dissolved in the rainwater that was falling at this time.Model results suggest that the reaction between uncomplexed Fe(III) and O 2 À was a significant source of Fe(II) during EisenEx and helped to maintain high levels of Fe(II) in the water column. This phenomenon may occur in iron enrichment experiments when two conditions are met: (i) When Fe is added to a system already saturated with regard to organic complexation and (ii) when mixing processes are slow, thereby reducing the dispersion of iron into under-saturated waters. D

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“…Renewed interest in assessing the role of iron in marine planktonic ecosystems was sparked by measurements suggesting that vast areas of the open ocean are iron limited (Martin and Fitzwater, 1988) and by results from the first in situ iron enrichment experiments conducted in the Equatorial Pacific, which showed stimulation of phytoplankton physiology and biomass (e.g., Kolber et al, 1994;Martin et al, 1994;Behrenfeld *Corresponding author. Tel.…”

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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Testing the iron hypothesis in ecosystems of the equatorial Pacific Ocean

Cited by 1,248 publications

References 39 publications

Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific

Iron limits the cell division rate of Prochlorococcus in the eastern equatorial Pacific

Spatial and temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment

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

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