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Global change

Iron uncertainty

Nature volume 406, pages 468–469 (2000)Cite this article

In these pages last week, there was an account1 of a new explanation2 for the lower levels of CO2 in the atmosphere during the last glaciation (about 130,000 to 20,000 years ago) compared with the ensuing interglacial3. Given that CO2 remains one of the main determinants of global warming, the matter is of obvious interest. The explanation held that it was the high availability of silica, rather than of iron4, that induced phytoplankton growth during the last glaciation. Results described by Loubere (page 497 of this issue5) show a different picture again, at least for the eastern equatorial Pacific Ocean (EEP); see the map on page 498. The EEP is an important area in terms of the high levels of both new ocean biological productivity (up to half of the global total) and ocean–atmosphere exchange of CO2.

Here I will concentrate on the iron-fertilization hypothesis, which for several years has been at the centre of debate among those studying climate change. The idea is that during glacial periods the land was drier and the winds stronger, meaning that more iron-containing dust was blown over the oceans. Iron is a limiting nutrient for phytoplankton photosynthesis, so its greater availability increases productivity in the ocean surface4. Increased productivity results in greater incorporation of CO2 into organic matter through photosynthesis. When the phytoplankton die or get eaten, some of their remains sink to the ocean bottom, effectively removing CO2 from contact with the atmosphere for a long time. The result, during glacial times, was lower concentrations of CO2 in the atmosphere.

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  1. Department of Geological and Environmental Sciences, Stanford University, Braun Hall (320) 207, Stanford, 94305-2115, California, USA

    Adina Paytan

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  1. Adina Paytan
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Correspondence to Adina Paytan.

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Paytan, A. Iron uncertainty. Nature 406, 468–469 (2000). https://doi.org/10.1038/35020176

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