BRINGING ON THE NEXT ICE AGE?
Dee Breger, Drexel University
Assumptions that tiny diatoms such as the ones shown above could fix carbon from the air and sink it to the bottom of the ocean have been hard to prove.
The US Department of Energy has taken an interest in carbon sequestration, but a grand scheme to induce thick blooms of carbon-fixing algae has yet to bear fruit in early studies. The DOE directs a large share of its global warming budget to carbon-sequestration research, drawing on biologists in hopes of enlisting algae, microbes, or plants to fix and store excess carbon created by the fossil-fuel economy. It has awarded tens of millions of dollars in biology-based research grants to geneticists, bioinformaticians, and cell biologists across the country.
By far the most ambitious and most expensive part of the program is a plan to seed the ocean with iron dust in order to induce phytoplankton blooms, which would in turn fix carbon and drop it to the bottom of the ocean. None of the four major iron fertilization expeditions has produced encouraging results. Problems abound, from a misunderstanding of the basic biochemical process involved, to faulty ecosystem modeling, to bacterial counter-blooms.
The idea can be traced back to a Woods Hole Oceanographic Institution meeting in 1985, when John Martin, then director of the Moss Landing Marine Laboratory, boasted: "Give me half a tanker of iron and I'll give you an ice age." Martin's general hypothesis that iron seeding would create a photosynthetic bloom proved correct, although the idea has turned out to be far less economical than he expected. The breakeven point for sequestration programs is $10 per ton of carbon dioxide; models based on the iron-seeding experiments still put the cost at $100 or more.
Many scientists involved in iron-seeding projects as well as those observing them from afar say that iron seeding for purposeful carbon sequestration just doesn't work. "In the beginning, the assumptions were that for every atom of iron, we could sink 500,000 atoms of carbon," says Ken Caldeira, an ocean carbon-cycle scientist at Lawrence Livermore National Laboratory in California, who helped to create computer simulations. Those estimates have since been revised downwards by hundreds of orders of magnitude, he says.
Sequestering carbon by any means necessary
Following the lead of President George W. Bush, whose $10 billion, 10-year 2002 Clear Skies and Global Climate Change initiative placed carbon removal at the top of the agenda, senior administrators at the Department of Energy (DOE) currently direct a majority of its global warming budget toward carbon-sequestration technology with far less going to alternative energy sources.
The DOE's 2005 budget, for example, includes $287 million for the Clean Coal Power Initiative, which is focused on sequestering carbon dioxide from coal furnaces, whereas funding for hydrogen energy research amounted to only $29 million. The largest projects currently focus on geological sequestration, in which excess carbon dioxide gets pumped into empty oil wells from whence it came. But, biologists factor in as well.
Grant Heffelfinger never considered himself a biologist. The Sandia National Laboratory software engineer spent most of his career helping to design and ensure safety measures for nuclear weapons. Now, among many other tasks, he oversees a $20 million DOE grant with the purpose of determining the carbon-fixation pathway for
This ocean cyanobacterium is no carbon-fixing powerhouse, but it has a completely sequenced genome. "The main aim of this project is to fully understand how this organism does it, and create the computational tools that can be used for other bacteria," says Heffelfinger. When marine biologists isolate a microbe that has a better-than-normal carbon-fixation mechanism, its sequence might be plugged into the software being developed by Heffelfinger's team and its pathway quickly determined. With discovery of different pathways, proteins, and genes comes the hope that an industrial microbe can be genetically engineered to sit inside a coal furnace and suck up all the carbon dioxide in the exhaust gases.
To realize this vision, though, researchers must find the microbes. That's why genome-sequencing maven, J. Craig Venter, is sailing the world aboard
Back on dry land, Rick Meilan, a forestry scientist at Purdue University, is trying to determine which genes in the recently sequenced
- Sam Jaffe
Others are more hopeful. Ken Coale, leader of the largest expedition to date, the Southern Ocean Iron Experiment (SOFeX), says that sequestration may still be viable. "Iron can be bought for pennies a ton," the current director of Moss Landing says. "It's still cheaper than any other method we've developed."
THE PRICE OF IRON
Yet, most ocean scientists side with Caldeira. The results of another large-scale experiment, the Subarctic Ecosystem Response to Iron Enrichment Study1 didn't do much to foster optimism. While the diatoms did respond dramatically to the iron additive, only 8% of the carbon material they produced fell below 50 meters, which is the minimum depth necessary for permanent sequestration. In addition, only four days passed between the end of the iron seeding and the expiration of the bloom. Scientists had been hoping that the bloom would endure much longer, but the silicic acid needed to produce the organisms' carbonate shells became depleted.
The results of SOFeX, also failed to show a massive flux in the carbon cycle.2 As a form of purposeful carbon sequestration, the authors pointed out that they were able to sink only 900 tons of carbon for the 1.26 tons of iron used in the experiment.
In addition, some question whether any of that carbon actually gets to the ocean floor. "There are entire ecosystems of microbes on each particle, and we really have no idea how much of it they consume as it falls from 50 meters to the sea floor, which can be 2000 meters below," says Kathy Barbeau, a marine chemist at Scripps Institution of Oceanography in La Jolla, Calif. The expedition was scientifically successful to a great degree. It proved Martin's original hypothesis again. It also was the first such expedition to get phytoplankton to bloom in an area of ocean that had low silicic acid content. "We expected that region to not bloom at all, and when it did everyone was surprised," says Rik Wanninkhof, an oceanic scientist at the National Oceanic and Atmospheric Administration who helped to tag the iron flakes with traceable chemicals. "It just goes to show how little of this process we understand."
A SIMPLE PLAN
The original idea behind iron seeding as a carbon mitigation strategy was to find areas of the ocean that are high in nitrates but low in chlorophyll, in other words, regions where nitrogen-fixing ocean bacteria are active but where little photosynthetic activity occurs. Approximately 20% of the ocean can be considered to fit these high-nitrate, low-chlorophyll criteria, according to Coale. The hypothesis is that little photosynthesis occurs in those regions, because they lack a suitable resource for the electron-transporting minerals necessary to make photosynthesis efficient.
© 2000 Nature Publishing Group
Above is a satellite view of the Southern Ocean Iron Enrichment Experiment (SOIREE) done in 1999 far off the southern coast of Australia. The algal bloom that resulted can be seen as a light semi circle.
Iron, even in trace amounts, is an ideal electron transporter. What hadn't been understood well, however, was the interplay between iron and other necessary nutrients, especially phosphates. "We knew that diatoms need phosphorous, but we thought there would be enough in the environment," says Caldeira. The natural supply appeared to expire quickly, however. The only corrective, he says, is to seed with phosphates in addition to iron, but the economics of such a system wouldn't work.
Even if someone were to figure out how to make algal blooms sequester carbon economically, very little research has been done on how such a project would affect the rest of the ecosystem. For instance, phytoplankton ecologist Elena Litchman at Georgia Institute of Technology in Atlanta ponders how the next level on the food ladder would react to a long-term artificially incurred algal bloom. She points out that mesozooplankton feed off of diatoms and might create a counter-bloom, producing as much carbon dioxide as the diatoms sequester. Such a change would then drastically affect the rest of the ecosystem. "It's a tangled mess of interactions that we have such a lack of knowledge about," says Litchman. "By altering one pathway, it could impact biological events in ways that nobody can imagine."
Sam Jaffe can be reached at