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Science 2 March 2007:
Vol. 315. no. 5816, p. 1234
DOI: 10.1126/science.1136328
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Brevia

Was There Really an Archean Phosphate Crisis?

Kurt O. Konhauser,1* Stefan V. Lalonde,1 Larry Amskold,1 Heinrich D. Holland2

During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted.

1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada.
2 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.

* To whom correspondence should be addressed. E-mail: kurtk{at}ualberta.ca

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