Iron Fertilization: Pumping Iron
Written by: Lisa Ayers Lawrence, Virginia Sea Grant, Virginia Institute of MarineScience
Credits:
Monterey Bay Aquarium Research Institute
Summary: Using data from the Monterey Bay Aquarium Research Institute, track chemical
changes during an upwelling event and investigate the effects of iron enrichment.
Introduction:
Pumping iron can make a person stronger and more fit. But can pumping iron into the
oceans improve the fitness of the Earth? Since the Industrial Revolution, humans have been
contributing significantly to global warming partly through the release of large amounts of CO2, a
greenhouse gas. In recent years, efforts have been made to reduce anthropogenic CO2 emissions
through conservation measures, including political agreements such as the Kyoto Protocol. In
addition to reducing the amount of CO2 produced, another way to limit this greenhouse gas is to find
methods of consuming it. A great way to consume CO2 is through photosynthesis by plants.
The oceans account for approximately 80% of the Earth's surface but only about 50% of primary
production. Large areas of the world's oceans, including the central ocean gyres, are not highly
productive due to low levels of the nutrients nitrogen and phosphorous. However, there are two areas,
the equatorial Pacific and the Southern Ocean, that have high nutrient levels yet still do not have high
phytoplankton productivity. (These areas are called HNLC -- high-nutrient, low-chlorophyll waters.)
Why is productivity lacking in spite of the presence of sufficient nutrients? Scientists, asking that
same question determined that these areas, though nutrient-rich, are lacking in iron. These scientists
came up with the Ocean Iron Fertilization Hypothesis to solve the problem.
The Iron Hypothesis theorizes that by adding iron to HNLC areas, phytoplankton productivity will
increase. As the phytoplankton photosynthesize, they take in CO2, incorporating the carbon into their
cells and releasing the oxygen to the water and atmosphere. Once the phytoplankton die, they sink
below the thermocline taking with them the atmospheric carbon which will remain stored in the deep
ocean for a long time. This process is called the biological pump. Benefits of ocean iron fertilization
could include not only an inexpensive method of reducing atmospheric CO2, but an increase in fish
stocks due to the increase in food. With such beneficial effects, why aren't scientists pumping iron
into the oceans like crazy?
Consider that it is extremely difficult to assess all the implications of deliberately altering such a
massive ecosystem. Many research issues remain. Fertilization of the oceans may cause not only
good phytoplankton blooms but also harmful algal blooms. In addition, when large phytoplankton
blooms die, oxygen is used during decomposition. This could lead to anoxic conditions like the Gulf
of Mexico's "dead zone." With anoxic conditions comes the release of methane and nitrous oxide,
two other greenhouse gases.
More research needs to be conducted on ocean iron fertilization to see if this is a viable solution. One
such research project is Monterey Bay Aquarium Research Institute's (MBARI) MOOS Upper-watercolumn Science Experiment (MUSE). The MUSE data show temperature, salinity, nitrate, iron and
chlorophyll content in waters just outside of Monterey Bay in California. The following data activity
analyzes selected MUSE data from August 2000 during upwelling and non-upwelling (relaxation)
events.
Data Activity:
The waters near Monterey Bay, California experience upwelling events that bring
cold, nutrient-rich water up from the bottom. During these upwelling events, the area experiences
HNLC (high-nutrient, low-chlorophyll) conditions. From August 18 - 26, 2000 the R/V New Horizon
sailed off the coast of Monterey Bay conducting the MUSE project. During this time, the area
experienced two upwelling events separated by a relaxation event.
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First upwelling event (Aug. 19/20):
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Relaxation Event (22:23 Aug):
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Compare the two sets of figures:
• During the upwelling, do temperature and nitrate (a form of nitrogen) levels differ between these two
events? Why?
• Are there large differences in the iron levels between these two events? Is iron being brought to the
surface during upwelling?
• Now compare the chlorophyll levels for these two periods. If the nutrient levels are higher during
upwelling, why might primary production be higher during relaxation?
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Second upwelling event
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• How do temperature, nitrate and iron differ from the first upwelling event? During which upwelling
event do the waters appear to be nitrogen-limited? During which upwelling event do the waters
appear to be iron-limited? During the research cruise, scientists collected samples of surface water and conducted iron enrichment
experiments in the lab to see if it was iron-limited. Sample A was collected during the first upwelling
event in high-nutrient waters, and sample B was collected during the second upwelling event in high-iron
waters. To each sample, iron was added (open circles) and chlorophyll levels were measured and
compared to controls with no iron enrichment (filled circles).
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• In sample A (high nitrogen), what effect did the addition of iron have on chlorophyll?
• Looking at the first 3 days, what effect did iron enrichment have on sample B? On day 3, nitrate was
added to sample B. How did that affect chlorophyll levels?
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EACH PERSON ANSWERS THIS QUESTION INDEPENDENTLY
• Based on these results do you think that it was appropriate for Ross George’s to convince the local
communities in Western Canada (discussed briefly in the video at the start of class) that
fertilizing their waters would help to increase salmon productivity? Why or why not? YOU
MUST INCLUDE DETAILED DEMONSTRATION OF YOUR UNDERSTANDING OF THE
CARBON CYCLE IN YOUR ANSWER.
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