Iron limitation of phytoplankton photosynthesis in the equatorial Pacific Ocean

THE surface waters of the equatorial Pacific have unusually high nitrate and phosphate concentrations, but relatively low phyto-plankton biomass 1–3 . This 'high nitrate, low chlorophyll' (HNLC) 4 phenomenon has been ascribed to 'top-down' grazing pressure by herbivores, which pr...

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Bibliographic Details
Published in:Nature (London) 1994-09, Vol.371 (6493), p.145-149
Main Authors: Kolber, Zbigniew S, Barber, Richard T, Coale, Kenneth H, Fitzwateri, Steve E, Greene, Richard M, Johnson, Kenneth S, Lindley, Steven, Falkowski, Paul G
Format: Article
Language:English
Subjects:
Chemistry
Energy conversion
Humanities and Social Sciences
Iron
letter
Marine
multidisciplinary
Oceans
Photochemicals
Photosynthesis
Phytoplankton
Plankton
Science
Science (multidisciplinary)
Surface water
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Summary:THE surface waters of the equatorial Pacific have unusually high nitrate and phosphate concentrations, but relatively low phyto-plankton biomass 1–3 . This 'high nitrate, low chlorophyll' (HNLC) 4 phenomenon has been ascribed to 'top-down' grazing pressure by herbivores, which prevent the phytoplankton from fully utilizing the available nutrients 5 . In the late 1980s, however, Martin and co-workers proposed that iron, which is delivered to the remote open ocean in aeolean dust 6 , is the key factor limiting the standing crop of phytoplankton in HNLC areas 7,8 . Using a sensitive fluor-escence method 9 , we have followed changes in photochemical energy conversion efficiency 9–10 of the natural phytoplankton com-munity both before and after artificial enrichment with iron of a small area (7.5 x 7.5 km) of the equatorial Pacific Ocean 11 . Our results show that iron limits phytoplankton photosynthesis in all size classes in this region by impairing intrinsic photochemical energy conversion, thereby supporting the hypothesis of physiologi-cal ('bottom up') limitation by this element.
ISSN:0028-0836
1476-4687
DOI:10.1038/371145a0