February 28, 2007
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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 12, NUMBER 2, FEBRUARY 1999
Community Structure and the Drawdown of Nutrients and CO2 in
the Southern Ocean, K. R. Arrigo et al., Science 283,
365-367 (Jan. 15, 1999).
Phytoplankton communities in the Ross Sea were found to display
preferences in the degree of mixing in the water in which they lived.
Diatoms prefer highly stratified waters, whereas Phaeocystis
antarctica assemblages preferred deeply mixed waters. The use of CO2
and nutrients and the rate of new production by diatoms are much lower
than by Phaeocystis. Thus, if upper-ocean stratification of the
Ross Sea should occur because of climate warming, transport of carbon to
the deep ocean could be dramatically curtailed.
Widespread Iron Limitation of Phytoplankton in the South Pacific
Ocean, M. J. Behrenfeld and Z. S. Kolber, Science 283,
840-843 (Feb. 5, 1999).
Physiological diagnostics were sought for limiting factors on primary
productivity in the oceans that can be used to readily survey vast areas.
Samples were taken during transects of the South Pacific and the Atlantic
oceans. The fluorescence rates, photochemical quantum efficiencies, and
functional absorption cross-sections of photosystem II of these samples
were measured. A diurnal cycle in photochemical quantum efficiencies was
noticed with a rapid decrease at sunset and an increase at sunrise; the
functional absorption cross-sections followed a similar course. During
each cycle, the fluorescence rates fluctuated widely, indicating that
quenching processes were reacting to irradiance saturation. When iron was
added to the samples, the decreases in photochemical quantum efficiencies
and functional absorption cross-sections disappeared. Tests on the samples
gathered indicate that iron deficiency limits primary productivity in much
of the South Pacific gyre.
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