So in summary, the N2-primed prokaryote
pump and the stochastic event-driven diatom pump, are probably the
most important with regard to discussions of ocean fertilization
I will now talk briefly about the Redfield Ratio pump because it
is the one we're used to thinking about. The Redfield Ratio concept
is a very important one in oceanography and I really don't have
time to review the entire history this morning. Dr. Paul Falkowski,
who is present here today, has recently written a beautiful summary
(Falkowski 2000, J. Phycol. 36, 3-6). This concept assumes that
there is a uniform biochemical stoichiometry of life in the ocean.
Biology ultimately controls the nutrient elements in the sea, and
there's been a cottage industry of studying the Redfield Ratio in
Now this is all well and good, and there's plenty of evidence that
the Redfield Ratio holds up in many parts of the world's oceans.
However, N2 fixation and the process
of denitrification (conversion of fixed N back into N2
gas) are two microbiological processes that can, over the long term,
disrupt the expected Redfield Ratio.
Furthermore, under phosphorus (P) limitation, which can occur in
many portions of the open ocean, the nitrogen-to-phosphorus (N:P)
molar ratio in organisms can increase well in excess of the Redfield
Ratio of 16N:1P, and under fixed N-limitation, it can decrease to
values below the Redfield Ratio.
these "anomalies," if you will, to the mean climatology
of the ocean are very important to our understanding of carbon sequestration
in the sea. At the top of this slide, I've presented a schematic
of the Redfield Ratio pump, wherein organic matter is produced and
exported all in Redfield Ratio, and is subsequently remineralized
with a similar C:N:P stoichiometry. The latter regenerated nutrient
pool feeds back into the surface ocean to continue the Redfield-balanced
production, export and remineralization cycle.
The Redfield stoichiometry pump has no potential for the net sequestration
of carbon, because the carbon that flow out of the euphotic zone
is equal to the carbon that flows back in, and everything is fully