Download Ocean Fertilization

Introduction
Since the advent of the Industrial Revolution, societies across the globe have thrived in increasing their production
capacity and, as a consequence, their contribution to global emissions of greenhouse gases. Consequently, the amount
of carbon dioxide in the atmosphere has increased from 280 parts per million (ppm) to 380 ppm, and the average
global surface temperature has increased by 0.8°C (Bala, 2009). These increases are the results of human
perturbations, and are likely to follow an upward trend over the upcoming years, leading to significant climate change
that would profoundly alter ecosystems all over the world. In the past 20 years, the growth rate of fossil fuel emissions
has increased from 1.3% per year in 1990 to 3.3% per year in 2006 (Canadell et al., 2007)
Geoengineering involves large scale engineering of the environment in order to combat or counteract the changes in
atmospheric chemistry (US National Academy of Sciences). In my previous report, I reviewed literature on the
specific geoengineering scheme of ocean fertilization. This technique actively targets carbon sequestration by storing
atmospheric CO2 in phytoplankton biomass, which will then be exported to the deep oceans through the biological
pump. Ocean fertilization consists of providing appropriate nutrients to increase the phytoplankton population, which
in turn increases the amount of carbon dioxide taken up from the atmosphere.While it seems to be a relatively simple
scheme, the potential problems and complications that accompany this geoengineering strategy are vast. They range
from testing issues due to scaling problems to environmental concerns, e.g. side effects such as ocean acidification and
eutrophication. Figure 1 synthesizes the outcomes of the main experiments performed in the field of ocean
fertilization.
Experiment
Southern Ocean Iron Experiment
(SOFeX) (2002)
Eisen Iron Experiment (EisenEx-1)
(2000)
Southern Ocean Iron Release Experiment
(SOIREE) (1999)
Outcome
The downward flux of carbon was similar in magnitude
to that of natural blooms and thus small relative to Earth
carbon budgets (Buesseler , 2004)
Limited evidence that the particles carried large
quantities of carbon to the deep ocean ( Dawicki, 2003)
No differences in the fluxes between fertilized and
nonfertilized waters (Buesseler, 2003)
Figure 1: Table showing the results from different fertilization experiments
This report analyses and critiques the science behind ocean fertilization, presented in the previous literature review. A
thorough discussion then leads to the final recommendation of further focused research in this field.
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Technical concerns
Scaling issue
Spatial scale, time scale, rate of addition, amount and concentration are all determinant factors that should be
considered while evaluating the oceanic impact of ocean fertilization. The results of small scale experiments (tens of
kilometers) are strongly influenced by the dilution of unfertilized water into the fertilized patch as well as mixing of
new chemicals, which makes it difficult to extrapolate the results to larger scales/timeframes (CBD, 2009). Most
importantly, many of the processes observed, especially carbon sequestration, do not scale linearly (CBD, 2009).
Therefore, “large scale” experiments provide more realistic estimates of the impacts from commercial scale
fertilization as well as a better assessment of the influence of surface manipulations on the sinking fluxes of particles.
Defining “Large scale”
All 12 small-scale experiments conducted in the field of ocean fertilization have not shown any side effects, mainly
because the latter are dissipated in the ocean’s vastness (Powell, 2007). Large scale experiments would allow
integrating many more factors and testing the behaviour of the oceanic system as a unit. There is currently no well
established definition of “large scale”; however, there is a scientific confidence that a “threshold scale” can be
determined such that fertilization up to this scale would likely not cause persistent changes to an ecosystem (IMO,
2010). The London Convention/ London Protocol Draft Assessment Framework provide a mechanism for assessing,
on a case-by-case basis, proposals for ocean fertilization to determine whether they represent legitimate scientific
research (IMO, 2010). This mechanism includes the evaluation of the following criteria (IMO, 2007):
1) The estimated amounts and potential impacts of iron and other materials that may be released with the iron.
2) The potential impacts of gases that may be produced by the expected phytoplankton blooms or by bacteria
decomposing the dead phytoplankton.
3) The estimated extent and potential impacts of bacterial decay of the expected phytoplankton blooms, including
reduced oxygen concentrations.
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4) The types of phytoplankton that are expected to bloom and the potential impacts of any harmful algal blooms that
may develop.
5) The nature and extent of potential impacts on the marine ecosystem including naturally occurring marine species
and communities.
6) The estimated amounts and timescales of carbon sequestration, taking account of partitioning between sediments
and water.
7) The estimated carbon mass balance for the operation.
Environmental issue
The effects of large-scale ocean fertilization are presently unknown and may not be reversible (IUCN, 2008). Even
individual ocean fertilization experiments could result in significant adverse impacts on the marine environment if
conducted inappropriately (Greenpeace, 2007). Another challenge lies in monitoring impacts of ocean fertilization
experiments. Fertilized patches move in three dimensions and current monitoring methods do not provide information
on the whole volume fertilized (IUCN, 2008). Unintended impacts may also occur beyond the fertilized patch and the
area being monitored.
Location
The concept of ocean fertilization only works in certain areas of the oceans where the deficiency of certain nutrients
(e.g. iron) is the main factor limiting plankton growth. Such areas are mostly found in the Southern Ocean, the subArctic North Pacific and the equatorial Pacific (CBD, 2009). The physical and biogeochemical conditions as well as
other factors such as the mixed layer depth, compensation depth and light penetration vary with location. Therefore,
the choice of location is a major player in the success of the fertilization experiment.
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Analysis
Ocean fertilization has many unintended consequences that are still unclear.
Side-Effects
Eutrophication and Oxygen Depletion
Ocean fertilization changes the nutrients input ratios, thus affecting the productivity and structure of the marine
ecosystem. The increase in concentration of the limiting nutrient can enhance algal biomass by as much as three orders
of magnitude (0.2 μg L−1 for natural waters compared to 200 μg L−1 for eutrophic waters) (Gilbert et al., 2008). The
algal bloom at the ocean surface reduces light penetration during the day, therefore preventing the transfer of energy to
the lower layers. During the night hours, algae continue to undergo cellular respiration and can consequently deplete
the water column of available oxygen. The high chlorophyll concentration is also associated with hypoxia and anoxia,
occurring as a result of an increase in the oxidation rate of organic matter by bacteria. The decomposition of organic
matter is coupled with the reduction of 02, which increases the oxygen demand in deep waters. “Dead Zones” are
formed when oxygen demand exceeds the supply of dissolved oxygen in the water column. Another consequence of
eutrophication is trophic downgrading, which results from the death of organisms at high trophic levels and their
replacement by phytoplankton at the lowest trophic level. Trophic downgrading is enhanced by the fact that algae
have a higher growth rate than zooplankton, their main predator, and are not efficiently transferred to higher trophic
levels, primarily due to the low trophic transfer efficiency ( not all algae are palatable to zooplankton , etc..) (Gilbert et
al., 2008) See figure 2.
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Figure 2 : The process of eutrophication as a result of an increase in supply of macronutrients such as Nitrogen and
Phosphorous. The increase in the decomposition rate of organic matter, due to phytoplankton bloom, leads to
enhanced oxygen consumption (by microorganisms) for the purpose of remineralisation (Killredtide.org).
Ocean Acidification
Ocean pH has fluctuated between 8.0 and 8.3 for the last 25 Million years (Lampitt, 2008). CO2 dissolved in the ocean
rapidly reacts with water to form carbonic acid, then dissociates into bicarbonate and carbonate ions. The respective
reaction equations are the following:
1st Reaction: Dissolution of CO2 in water, producing carbonic acid
CO2 + H2O
H2CO3
2nd Reaction: Dissociation of carbonic acid, releasing hydrogen ions and bicarbonate
H2CO3
HCO3− + H+
3rd Reaction: Dissociation of Bicarbonate, releasing hydrogen ions and Carbonate ions
HCO3−
H+ + CO32-
These reactions add H+ ions (i.e. protons) to the oceans, thereby reducing pH and increasing acidity1.
The resulting net decrease in pH will also have negative consequences on oceanic calcifying organisms, which build
their external skeletal material out of calcium carbonate (CaCO3)(Hofman et al., 2010). These organisms span the food
chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera,
echinoderms, crustaceans and molluscs. Under normal conditions, the surface ocean is saturated in calcium carbonate
(including its several mineral forms such as calcite and aragonite), providing enough calcium and carbonate ions for
calcifying marine organisms, thus preventing corrosion of their shells (Hofman et al., 2010). The increase in oceanic
CO2 absorption due to fertilization considerably raises the concentration of H+ ions, which stimulates their reaction
with carbonate ions to reform bicarbonate: H+ + CO32-
HCO3−. With the smaller amount of carbonate ions
available, structures made of calcium carbonate such as coral reefs are deprived of their growth source as well as
vulnerable to dissolution.
The pH log scale, pH=-log[H+], means that for every unit decrease on the pH scale, the hydrogen ion concentration has
increased 10 folds
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Figure 3: Graph displaying the proportion of the saturating concentrations for three dissolved inorganic compounds
CO2, HCO3- and CO32- as a function of the ocean/seawater pH. A shift to the right or a decrease in acidity is due to an
increase in the concentration of CO32- and a decrease in the concentration of CO2. A shift to the left or an increase in
acidity is due to a decrease in the concentration of CO32- and an increase in the concentration of CO2. The latter is a
consequence of ocean fertilization (Friedland, 2010).
Production of climate-relevant gases
Ocean fertilization enhances the production of potent greenhouse gases nitrous oxide (N2O) and methane (CH4),
which are respectively 300 times and 25 times more effective as greenhouse gases than carbon dioxide (Greenpeace,
2007). Much of the methane and nitrous oxide arise from microbial activity in and around sinking particles of
particulate carbon. Anaerobic conditions stimulate denitrification, the conversion of Nitrate and Nitrite to Nitrous
oxide then Nitrogen gas , and methanogenesis, the production of methane by methanogens during the last step in the
decay of organic matter (EPA, 2010). Ocean fertilization spurs the export rate of organic materials, thereby expanding
low oxygen zones (by prompting mineralisation). In some regions of the ocean, large areas of surface water can
become oxygen depleted, allowing active denitrification and methanogenesis in open water and leading to rising
nitrous oxide and methane emissions.
Additionally, some phytoplankton classes, such as Dinophycease and Prymnesiophycea might produce more of a
chemical called dimethylsulfide (DMS), which can drift into the atmosphere and encourage cloud formation, thus
cooling the atmosphere and helping to counteract greenhouse warming (EPA, 2010). One way of evaluating the effect
of each gas is through radiative forcing, which is a measure of the influence of that gas in altering the balance of
incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the gas in climate
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change (IPCC). Ocean fertilization is likely to alter the concentrations of gases and aerosols affecting the radiative
balance of the Earth (Lampitt, 2008). The following figure summarizes the expected variations.
Radiative Forcing
2
1.5
1
Radiative Forcing
0.5
0
CO2
CH4
DMS
NO2
Figure 4 : Chart displaying the change in radiative forcing in (W/m2) for different gases with respect to preindustrial
conditions defined at 1750. (Lampitt, 2008)
Test Experiments
Comparison experiments
One way of testing ocean fertilization would be to perform the same experiment (i.e. add the same amount and type of
fertilizer) in multiple locations and compare the magnitude of the photosynthetic phytoplankton bloom and side
effects. This approach will enable the division of the oceans into different “fertilization regions” that have a common
limiting nutrient.
Gradual Scaling
Another way of testing ocean fertilization would be to gradually scale up the experiments until the wanted parameters,
such as the rate of gas production, the storage time of carbon, the change in pH and CO32- concentration, become
measurable with the available tools. An alternative to this would be to develop complex apparatuses capable of
measuring these parameters with greater precision, thus making small-scale experiments fully exploitable.
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Artificial Upwelling
Instead of providing fertilizers to enhance the downward flux of carbon, one could also exploit the motion of waves to
bring up nutrients from deep waters to the surface. British scientists James Lovelock and Chris Rapley developed a
whole new concept based on that idea. Long tubes extending from the nutrient-poor surface to nutrient-rich cold
waters would allow the pumping of deep water through the harnessing of wave energy. Although this method seems to
mimic anthropogenic nutrient addition, it does not guarantee the wanted kind of biological growth (i.e. photosynthetic
picoplankton) at the surface (ScienceDaily, 2009). This is due to the upwelling of random nutrients from the deep
ocean. This same method can also bring up water enriched with carbon dioxide, which can de-gas into the atmosphere.
One way of avoiding the upwelling of unwanted elements would be to pump water that contains specific ratios of
nutrients (particularly nitrogen and phosphorus), instead of carbon dioxide, by targeting different depths
(ScienceDaily, 2009).
Conclusion and Recommendation
The investigation of ocean fertilization indicates that the level of scientific understanding is insufficient to recommend
its potential use for carbon sequestration. Based on this observation, I recommend further focused research in that
field. This research should be conducted at a sufficiently large scale that will enable the assessment of the different
parameters (i.e. the rate of gas production, the storage time of carbon, the change in pH and CO32- concentration, etc...)
The research should also target specific aspects of the carbon storage process including the downward carbon flux, the
storage time of carbon, the ocean acidity, the concentration of CO32- , the oxygen concentration and gas emissions.
I strongly advocate that scientific research into ocean fertilization include both macronutrient and micronutrient
fertilization. The two types of fertilization are considerably different and applicable in diverse regions of the world.
One promising experiment to look into would be the use of tubes to enhance upwelling of nutrients, mainly because it
seems more durable than other fertilization means. This experiment will also allow a better understanding of natural
systems such as the biological pump. This being said, researching the topic of ocean fertilization should be given
priority over other geoengineering topics since it involves a much more complex system of interaction that is still
unclear.
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Annexe
Works Cited

Bala, G. "Problems with Geoengineering Schemes to Combat Climate Change." Current science 96.1 (2009):
41-8.

Buesseler, Ken O., et al. "The Effects of Iron Fertilization on Carbon Sequestration in the Southern Ocean."
Science 304.5669 (2004): 414-7.

Buesseler, Ken O., and Philip W. Boyd. "Will Ocean Fertilization Work?" Science 300.5616 (2003): 67-8.

Glibert, Patricia M., et al. "Ocean Urea Fertilization for Carbon Credits Poses High Ecological Risks."
Marine pollution bulletin 56.6 (2008): 1049-56.

Lampitt, R. S., et al. "Ocean Fertilization: A Potential Means of Geoengineering?" Philosophical Transactions
of the Royal Society A: Mathematical, Physical and Engineering Sciences 366.1882 (2008): 3919-45.

Dawicki, “Will Ocean Fertilization To Remove Carbon Dioxide From the Atmosphere Work?” Woods Hole
Oceanographic Institution (WHOI) 2003

United States Environmental Protection Agency (EPA), “Methane and Nitrous Oxide Emissions From
Natural Sources” 2010

Greenpeace Research Laboratories, “A scientific critique of oceanic iron fertilization as a climate change
mitigation strategy” 2007

International Maritime Organization (IMO), “Ocean fertilization: assessment framework for scientific
research involving ocean fertilization” 2010

International Maritime Organization (IMO), “Convention on the prevention of maritime pollution”, July 2007

Friedland, “Ocean Acidification”, The Political Climate 2010

Romm, “Ocean Fertilization for Geoengineering should be abandoned”, Climate Progress 2009

Hofman, “The Effect of Ocean Acidification on Calcifying Organisms in Marine Ecosystems: An Organismto-Ecosystem Perspective” 2010

Cannadel, The Global Carbon Cycle : Integrating Humans, Climate, and the Natural World. Washington, DC:
Island Press, 2007
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
The Convention on Biological Diversity (CBD), “Scientific Synthesis on the impacts of ocean fertilization on
marine biodiversity”, 2009

International Union for Conservation of Nature (IUCN), “Ocean Fertilization : Engineering the world’s
climate” , December 2008

ScienceDaily, “Complex Ocean Behavior Studied With Artificial Upwelling”, September 2008


The US National Academy of Sciences
Killredtide.org
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