This is the equivalent to a postage stamp on
the area of Texas. If you're a cell and you need iron to survive,
it'd be like flying over Texas looking for a postage stamp.
In addition, these extremely low concentrations poses an analytical
challenge to chemists measuring its concentration and many of us
are struggling to develop chemical methods for the analysis that
are robust and can use at sea.
reiterate some earlier points, this slide shows the stoichiometry
of photosynthesis and respiration including the iron requirement
for phytoplankton. The upper portion depicts photosynthesis indicating
a conversion of CO2 into organic Carbon material that sinks from
the water column into the deep ocean. To illustrate the molar ratio
of Fe:CO2 required by a phytoplankton cell, you can move 20,000
carbon dioxide molecules over to this side of the equation with
one iron atom in the coastal zone, and perhaps in the open ocean
you can move 500,000 CO2 atoms with one iron atom.
This is an incredible leveraging of iron by the cell in a very
delicate biological system. The point here is that very little iron
is required to fix a lot of carbon dioxide.
What does this mean in ocean systems? In this gross oversimplification
of the carbon cycle, we see the atmosphere represents about 700
metric tons of carbon, and acts as a reservoir.
oceans, by far, have the largest reservoir of carbon, which is accessible
in the biosphere, representing about 38,000 metric tons of carbon.
What I want to emphasize here is that small differences in the
balance of these carbon reservoirs can make huge differences in
terms of climate.
is a schematic diagram of the biological pump in the ocean. These
are complex, linked processes that result in the transport of carbon
fixed in the surface water by phytoplankton to the deep ocean. If
we turn-up the biological pump to drive more CO2 into the oceans,
CO2 in the atmosphere may decrease.
Note that only a fraction of that CO2 that is incorporated via
the biological pump actually exits into the deep sea and may in
fact be sequestered.