IRON SEEDING (FERTILIZATION)
OF THE OCEAN
Iron fertilization is the intentional introduction
of iron to the upper ocean to increase the marine food chain and
to sequester carbon dioxide from the atmosphere. It involves encouraging
the growth of marine phytoplankton blooms by physically distributing
microscopic iron particles in otherwise nutrient rich, but iron
deficient blue ocean waters.
An increasing number of ocean labs, scientists
and businesses are exploring it as a means to revive declining plankton
populations, restore healthy levels of marine productivity and/or
sequester millions of tonnes of carbon dioxide to slow down global
warming. Since 1993, ten international research teams have completed
relatively small-scale ocean trials demonstrating the effect, and
substantially larger pilot projects were planned.
Iron seeding of oceans and climate change
As John Martin envisioned from his water research
and the paleoclimatological record, increasing plankton photosynthesis
and primary productivity could have profound impacts on atmospheric
carbon dioxide and global temperature.
Historically marine phytoplankton have annually
absorbed and fixed nearly half of all planetary carbon dioxide emissions
or approximately 50 billion tons. NASA and NOAA’s most conservative
estimate of global plankton decline in the last 25 years is at least
6%. Simply returning these populations to known 1980 levels of health
and activity could therefore annually sequester 2~3 billion more
tons of carbon dioxide than are being removed today, or a third
to one half of all current industrial and automotive emissions.
Also, water with more algae would reflect more sunlight and cause
less heating of the ocean.
Plankton that generate calcium or silica carbonate
skeletons, such as diatoms, coccolithophores and foraminifera, account
for most direct carbon sequestration. When these organisms die their
carbonate skeletons sink relatively quickly and form a major component
of the carbon-rich deep sea precipitation known as marine snow.
Marine snow also includes fish fecal pellets and other organic detritus,
and can be seen steadily falling thousands of meters below active
Of the carbon-rich biomass generated by natural
plankton blooms and fertilization events, half or more is generally
consumed by grazing organisms (zooplankton, krill, small fish, etc.)
but 20 to 30% sinks below 200 meters into the colder water strata
below the thermocline. Much of this fixed carbon continues falling
into the abyss as marine snow, but a substantial percentage is redissolved
and remineralized. At this depth, however, this carbon is now suspended
in deep currents and effectively isolated from the atmosphere for
centuries or more. (The surface to benthic depths cycling time for
the entire ocean system is approximately 4000 years.)
Analysis and quantification: Evaluation of the
biological effects and verification of the amount of carbon actually
sequestered by any particular bloom requires a variety of sophisticated
measurements. Methods currently in use include a combination of
ship-borne and remote sampling, submarine filtration traps, tracking
buoy spectroscopy, and satellite telemetry.
Dimethyl sulfide and clouds
Some species of plankton produce Dimethyl sulfide
(DMS), a portion of which enters the atmosphere where it is oxidized
by hydroxyl radicals (OH), atomic chlorine (Cl) and bromine monoxide
(BrO) to form sulfate particles and ultimately clouds. This may
increase the amount of sunlight reflected from the planet and so
During the Southern Ocean Iron Enrichment Experiments
(SOFeX), DMS concentrations increased by a factor of four inside
the fertilized patch. Widescale iron fertilization of the Southern
Ocean could lead to significant cooling in addition to the increased
carbon dioxide uptake, however the amount of cooling is very uncertain.
how much would it cost?
Current estimates of the amount of iron required
to restore all the lost plankton and sequester 3 gigatons of carbon
dioxide range widely, from approximately two hundred thousand tons/year
to over 4 million tons/year. Even in the latter worst case scenario,
this only represents about 16 supertanker loads of iron and a projected
cost of less than €20 billion. Considering EU penalties for Kyoto
non-compliance will reach €100/ton carbon dioxide in 2010 and the
annual value of the global carbon credit market is projected to
exceed €1 trillion by 2012, even the most conservative estimate
still portrays a very feasible and inexpensive strategy to offset
half of all industrial emissions.
History of iron fertilization of oceans
Consideration of iron’s importance to phytoplankton
growth and photosynthesis dates back to the 1930s when English biologist
Joseph Hart speculated that the ocean’s great “desolate zones” (areas
apparently rich in nutrients, but lacking in plankton activity or
other sea life) might simply be iron deficient. Little further scientific
discussion of this issue was recorded until the 1980s, when oceanographer
John Martin renewed controversy on the topic with his marine water
nutrient analyses. His studies indicated it was indeed a scarcity
of iron micronutrient that was limiting phytoplankton growth and
overall productivity in these “desolate” regions, which came to
be called “High Nutrient, Low Chlorophyll” (HNLC) zones.
Martin’s famous 1991 quip at Woods Hole Oceanographic
Institution, “Give me a half a tanker of iron and I will give you
another ice age,” vernacularized a decade of research findings that
suggested iron deficiency was not merely impacting ocean ecosystems,
it also offered a key to mitigating climate change as well. Martin
hypothesized that restoring high levels of plankton photosynthesis
could slow or even reverse global warming by sequestering enormous
volumes of carbon dioxide in the sea. He died shortly thereafter
during preparations for Ironex I, a proof of concept research voyage,
which was successfully carried out near the Galapagos Islands in
1993 by his colleagues at Moss Landing Marine Laboratories. Since
then 9 other international ocean trials have confirmed the iron
Perhaps the most dramatic vindication of Martin’s
hypothesis was seen in the aftermath of the 1991 eruption of Mount
Pinatubo in the Philippines. Environmental scientist Andrew Watson
analyzed global data from that eruption and calculated that it deposited
approximately 40,000 tons of iron dust into the oceans worldwide.
This single fertilization event generated an easily observed global
decline in atmospheric carbon dioxide and a parallel pulsed increase
in oxygen levels.
Financial opportunities of iron fertilization
Since the advent of the Kyoto Protocol several
countries and the European Union have established carbon offset
markets which trade certified emission reduction credits (CERs)
and other types of carbon credit instruments internationally. In
2006 CERs sell for approximately €25/ton carbon dioxide, which suggests
that a full-scale plankton restoration program could generate up
to €75 billion in carbon offset value. Iron fertilization is a relatively
inexpensive carbon sequestration technology compared to scrubbing,
direct injection and other industrial approaches, and can theoretically
generate these credits for less than €5/ton. Given this potential
return on investment, some carbon traders and offset customers are
watching the progress of this technology with interest.
Science of iron fertilization
About 70% of the world’s surface is covered in
oceans, and the upper part of these (where light can penetrates)
is inhabited by algae. In some oceans, the growth and/or reproduction
of these algae is limited by the amount of iron in the seawater.
Iron is a vital micronutrient for phytoplankton growth and photosynthesis
that has historically been delivered to the pelagic sea by wind-driven
dust storms from arid lands. This Aeolian dust contains 3~5% iron
and its deposition has fallen nearly 25% in recent decades due to
modern changes in land use and agricultural practices as well as
increased greening of dry regions thanks to increasing levels of
atmospheric carbon dioxide. (Arid zone grasses and vegetation now
lose less water vapor through their stomata to absorb the same amount
of carbon dioxide, and thus stay greener longer, reducing dust storm
frequency and the amount of iron reaching the deep seas. Increasing
sand desertification does little to compensate for this shortfall
since sand is primarily silica with relatively low iron content.)
In “desolate” HNLC zones, therefore, small amounts
of iron (measured in parts per trillion) delivered by either by
the wind or a planned restoration program can trigger large responsive
phytoplankton blooms. Recent marine trials confirm that one kilogram
of fine iron particles can reliably generate well over 100,000 kilograms
of plankton biomass. The size of the iron particles is critical,
however, and particles of several micrometers or less seem to be
ideal both in terms of sink rate and bioavailability. Particles
this small are not only easier for cyanobacteria and other phytoplankton
to incorporate, the churning of surface waters keeps them in the
euphotic or sunlit biologically active depths without sinking for
long periods of time.
Debate over iron fertilization
While many advocates of ocean iron fertilization
see it as modern society’s last best hope to slow global warming
long enough to change our consumption patterns and energy systems,
a number of critics have also arisen including some academics, deep
greens and proponents of competing technologies who cite a variety
Critics say we don’t know the possible side-effects
of large scale iron fertilization. Not enough research has been
done. We should not risk iron fertilization on the scale needed
to affect global carbon dioxide levels or animal populations.
Advocates: believe that similar blooms have occurred
naturally for millions of years with no observed ill effects. The
precautionary principle provides a legitimate brake on this technique
once plankton populations are restored to their known levels in
1980. Up to that point, however, plankton revival is simply eco-healing
and little different from remedially treating superfund sites, oil
spills or contaminated mothers milk. Not even trying to remedy these
industrial impacts is far more irresponsible considering the known
pace of increasing harm.
Inadequacies of carbon sequestration
According to certain ocean iron fertilization
trial reports, this approach may actually sequester very little
carbon per bloom, with most of the plankton being eaten rather than
deposited on the ocean floor, and thus require too many seeding
voyages to be practical.
The counter-argument to this is that the low sequestration
estimates that emerged from some ocean trials are largely due to
Timing: none of the ocean trials had enough boat
time to monitor their blooms for more than 27 days, and all their
measurements are confined to those early weeks. Blooms generally
last 60~90 days with the heaviest precipitation occurring during
the last two months.
Scale: most trials used less than 1000 kg of iron and thus created
small blooms that were quickly devoured by opportunistic zooplankton,
krill and fish that swarmed into the seeded region.
Academic conservatism: having an obviously limited data set and
unique sequestration criteria, many peer-reviewed ocean researchers
are understandably reluctant to project or speculate upon the results
their experiments might have actually achieved during the full course
of a bloom.
Some ocean trials did indeed report remarkable results. According
to IronEx II reports, their thousand kilogram iron contribution
to the equatorial Pacific generated a carbonaceous biomass equivalent
to one hundred full-grown redwoods within the first two weeks. Researchers
on Wegener Institute’s 2004 Eifex experiment recorded carbon dioxide
to iron fixation ratios of nearly 300,000 to 1.
Critics say that in ocean science, carbon is not
considered removed from the system unless it settles to the ocean
floor where it is truly sequestered for eons. Most of the organic
and inorganic carbon that sinks beneath plankton blooms is dissolved
and remineralized at great depths and will eventually be re-released
to the atmosphere, negating the original effect.
Advocates say ocean science does traditionally
define “sequestration” in terms of sea floor sediment that is isolated
from the atmosphere for millions of years. Modern climate scientists
and Kyoto Protocol policy makers, however, define sequestration
in much shorter time frames and recognize trees and even grasslands
as important carbon sinks. Forest biomass only sequesters carbon
for decades, but carbon that sinks below the marine thermocline
(100~200 meters) is effectively removed from the atmosphere for
hundreds or thousands of years, whether it is remineralized or not.
Since deep ocean currents take so long to resurface, their carbon
content is effectively “sequestered” by any terrestrial criterion
in use today.
Harmful Algal Blooms
Critics believe that some plankton species cause
red tides and other toxic phenomena. How do we know what kind of
plankton will bloom in these events? What will prevent toxic species
from poisoning lagoons, tide pools and other sensitive ecosystems
along our coasts?
Advocates believe most species of phytoplankton
are entirely harmless, and indeed beneficial. Red tides and other
harmful algal blooms are largely coastal phenomena and primarily
affect creatures that eat contaminated coastal shellfish. Iron-stimulated
plankton blooms only work in the deep oceans where iron deficiency
is the problem. Most coastal waters are replete with iron and adding
more has no effect. Since all phytoplankton blooms last only 90~120
days at most, in the open ocean fertilized patches of any species
will dissipate long before reaching any land.
Deep water oxygen depletion
Critics believe that when organic bloom detritus
sinks into the abyss, a significant fraction will be devoured by
bacteria, other microorganisms and deep sea animals which also consume
oxygen. A large bloom could, therefore, render certain regions of
the sea deep beneath it anoxic and threaten other benthic species.
Advocates believe the largest plankton replenishment
projects now being proposed are less than 10% the size of most natural
wind-fed blooms. In the wake of major dust storms, many extremely
vast natural blooms have been studied since the beginning of the
20th century and no such deep water die offs have ever been reported.
Critics say depending upon the composition and
timing of delivery, these iron infusions could preferentially favor
certain species and alter surface ecosystems to unknown effect.
Population explosions of jellyfish, disturbance of the food chain
with a huge impact on whale populations or fisheries are cited as
Advocates say carbon dioxide-induced surface water
heating and rising carbonic acidity are already shifting population
distributions for phytoplankton, zooplankton and many other creatures
on a massive scale.
If certain infusions or space/time coordinates
do show asymmetrical selective impacts in certain regions, the effect
is inherently constrained by the limited size and 90-day lifespan
of each bloom. Only larger scale research will show if this is really
a problem, what factors tilt the playing field, and/or whether this
issue can be effectively addressed.
Conclusion and further research
Advocates say that using this technique to restore
ocean plankton to recent known levels of health would help solve
half the climate change problem, revive major fisheries and cetacean
populations, and alleviate several other urgent ocean crises. Critics
say global warming must be solved at the source, large scale iron
fertilization experiments have never been attempted, the effects
could be inadequate, and/or too little is known to press ahead.
Critics and advocates generally agree that most
outstanding questions on the impact, safety and efficacy of ocean
iron fertilization can only be answered by much larger studies.
Several such large scale pilot projects (covering approximately
10,000 km²) were organized for 2006 and 2007 in collaboration with
various ocean institutes and university laboratories.
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