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Item #d96dec14

Five related items in Nature, 383(6600), Oct. 10, 1996 (see News, this Global Climate Change Digest issue--Dec. 1996):

"Phytoplankton Bloom on Iron Rations," B.W. Frost (Sch. Oceanog., Univ. Washington, Seattle WA 98195), 475-476. Summary of and comment on the results of the IronEx II experiment in the Equatorial Pacific, detailed in the following four papers.

"A Massive Phytoplankton Bloom Induced by an Ecosystem-Scale Iron Fertilization Experiment in the Equatorial Pacific Ocean," K.H. Coale (Moss Landing Marine Labs., POB 450, Moss Landing CA 95039), K.S. Johnson et al., 495-501. The seeding of an expanse of surface waters with low concentrations of dissolved iron, but high nitrate and low chlorophyll, triggered a massive phytoplankton bloom. It consumed large quantities of CO2 and nitrate that these microscopic plants cannot fully utilize under natural conditions. These and other observations provide unequivocal support for the hypothesis (which now takes the status of a theory) that phytoplankton growth in this oceanic region is limited by iron bioavailability.

"Confirmation of Iron Limitations of Phytoplankton Photosynthesis in the Equatorial Pacific Ocean," M.J. Behrenfeld (Oceanog. & Atmos. Sci. Div., Brookhaven Natl. Lab, Upton NY 11973), A.J. Bale et al., 508-511. Focuses on in situ measurements of fluorescence in Iron Ex II, which show that the iron enrichment triggered biophysical alterations of the phytoplankton's photosynthetic apparatus, resulting in increased photosynthetic capacities throughout the experiment and the observed bloom.

"Large Decrease in Ocean-Surface CO2 Fugacity in Response to in situ Iron Fertilization," D.J. Cooper (Dept. Atmos. & Ocean Sci., Univ. Wisconsin, 1225 W. Dayton St., Madison WI 53706), A.J. Watson, P.D. Nightingale, 511-513. The fugacity of CO2 in the center of the IronEx II bloom fell significantly, implying a transient 60% decrease in the natural ocean-to-atmosphere CO2 flux. Concludes that the iron supply to this ocean region can strongly modulate the local short-term source of CO2 to the atmosphere. There is little long-term influence on the partial pressure of atmospheric CO2 here, but there could be in the Southern Ocean.

"Increased Dimethyl Sulphide [DMS] Concentrations in Sea Water from in situ Iron Enrichment," S.M. Turner (Sch. Environ. Sci., Univ. E. Anglia, Norwich NR4 7TJ, UK), P.D. Nightingale et al., 513-517. Iron enrichment increased DMS concentrations by a factor of 3.5. Results provide direct support for an important link in the iron-DMS-climate hypothesis, in which natural iron fertilization by dust influences global albedo and temperature change by the transformation of DMS to sulfate aerosol particles in the atmosphere.

Item #d96dec15

Two related items in Nature, 383(6598), Sep. 26, 1996:

"Microbial Ferrous Wheel," D.L. Kirchman (Graduate College of Marine Studies, Univ. Delaware, Lewes DE 19958), 303-304. Provides a research background for the following paper, which decisively establishes oceanic bacteria as a component of the "biological pump," which exports carbon and other materials to the deep ocean.

"The Role of Heterotrophic Bacteria in Iron-Limited Ocean Ecosystems," P.D. Tortell (Dept. Ecol. & Evolutionary Biol., Princeton Univ., Princeton NJ 08544), p. 330 ff. Measurements in the subarctic Pacific Ocean and in the laboratory show that heterotrophic bacteria, which constitute up to 50% of the total particulate organic carbon in open ocean waters, play a major role in the biogeochemical cycling of iron. Iron limitation of heterotrophic metabolism may have profound effects on carbon flux in the ocean.

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