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FROM VOLUME 9, NUMBER 12, DECEMBER 1996
related items in Nature, 383(6600), Oct. 10, 1996
(see News, this Global Climate Change Digest issue--Dec.
"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
"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.
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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