DATA Series

Summary
Using data from the Monterey Bay Aquarium Research Institute, track chemical changes during an upwelling event and investigate the effects of iron enrichment.

Objectives

• Describe ocean iron fertilization, the biological pump and upwelling.
• Relate roles of phytoplankton productivity and upwelling.
• Distinguish among differences in chlorophyll, temperature, nitrate and iron levels during and after upwelling events.
• Appraise the value and impact of iron on chlorophyll levels.

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-water-column 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.

Access MBARI’s wind direction data from this time period.

1. How do wind direction and speed change from the upwelling events to the relaxation events? Access MBARI’s surface contour data for the first upwelling event and the relaxation event.
2. Do temperature and nitrate (a form of nitrogen) levels differ between these two events? Why?
3. Are there large differences in the iron levels between these two events? Is iron being brought to the surface during upwelling?
4. 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?
5. Access MBARI’s surface contour data for the second upwelling event. 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. Access the enrichment experiment data. 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).

6. In sample A (high nitrogen), what effect did the addition of iron have on chlorophyll?
7. 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?
8. Based on your analysis of these data, do you think iron fertilization of the waters off of Monterey Bay, California would increase primary productivity?
9. What other experiments might you do to see if this would be beneficial?

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