DUMPING IRON INTO OCEAN COULD HELP SEQUESTER CO2 FOR CENTURIES, RESEARCHERS SAY

Tamar Hallerman
GHG Monitor
07/27/12

A group of international researchers has issued a new study that says adding iron to portions of the ocean could cause an algae boom that could eventually lead to the sequestration of carbon already emitted into the atmosphere. In a study published in the most recent edition of the journal Nature, a team of researchers from more than a dozen nations analyzed results from an ocean iron fertilization (OIF) experiment conducted in the South Ocean surrounding Antarctica eight years ago. Over the course of five weeks, the team “fertilized” a 37 mile-wide self-contained eddy with several tonnes of iron sulphate. Because the waters in the region are nutrient-rich but relatively deplete of iron, the addition spurred the creation of twice the amount of blooms of single-celled algae than average. The team then monitored the blooms during photosynthesis, as they took in CO2 from the atmosphere; and as they died several weeks later, sinking miles below to the bottom of the deep ocean. At least half of the blooms sank to depths of below 3,300 feet, with a “substantial” portion likely to have reached the seafloor, in effect sequestering the CO2 the algae absorbed that could last for a period of centuries, the researchers said. “Iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments,” the report concludes.

In an interview with GHG Monitor, the head authors of the study, Christine Klaas and Victor Smetacek of the Alfred Wegener Institute for Polar and Marine Research in northwest Germany, said that while previous experiments had linked iron additions with increased algae blooms in low-iron waters, this study has helped prove that the CO2 absorbed by that algae is then sequestered deep underwater. “Based on previous experiments, we knew that when iron was added, a bloom of algae grew. But those experiments never showed there was a significant increase in the export of this organic matter at depth,” Klaas said. “This is the first time we proved that.” She added that the monitoring portion of the experiment, the longest of its kind ever conducted in an ocean, also showed higher levels of biomass accumulation than in other experiments.

Researchers Tout OIF’s Potential

While much more research must be done, OIF could become a fairly efficient method of mitigating CO2 emissions, the researchers said. The report said that each atom of additional iron put into the ocean absorbed at least 13,000 atoms of CO2 from the atmosphere, and that OIF has the potential of sequestering up to 1 gigatonne of CO2 annually, making this an option that should not be ignored, Smetacek said. “While 1 gigatonne is not going to save the world, it is also too large to ignore,” he said. “So one would definitely have to consider it. While it’s not going to be the solution, it could be part of a portfolio of measures undertaken [to mitigate climate change].”

Ken Buesseler, a marine scientist at the Woods Hole Oceanographic Institution who has done work on the issue in the past but is not affiliated with the study, told GHG Monitor that the project has made the link between OIF and removing CO2 from the atmosphere “probably better than anyone else.” In a corresponding commentary piece in Nature this week, he said that the work is significant because it answers some questions about whether OIF is a viable climate change strategy. “[It] certainly does not answer all of the questions about geoengineer¬ing, but by showing how the addition of iron to the ocean not only enhances ocean productiv¬ity, but also sequesters carbon, it is one of the best OIF studies so far,” Buesseler said in his commentary.

Questions Still Remain

The study, however, still leaves some questions unanswered about the viability about OIF. For one, concrete figures for the carbon sequestration aspect—how much carbon stays out of the atmosphere and for how long—still do not exist. Klaas said that much depends on the depth to which the algae bloom sinks. “In the Southern Ocean, the portion of CO2 retained within the 200-m-deep winter mixed layer would be in contact with the atmosphere within months, but carbon sinking to successively deeper layers, and finally the sediments, will be sequestered for decades to centuries or longer,” the report says.

Another unresolved question, as pointed out by Buesseler in his commentary, is the issue of unintended side effects surrounding OIF. “Although the authors conclude that OIF does indeed sequester carbon in the deep ocean, questions remain about the possible unintended consequences of geoengineer¬ing,” he said, listing things like the production of nitrous oxide, a more potent greenhouse gas than CO2, the possibility of the creation of toxic algal blooms and the potential to deplete oxygen levels in mid-waters as the algae decomposes. Buesseler told GHG Monitor that scaling also could bring forth some significant challenges. “If you were to geoengineer, you’d need to do this on a much larger scale, and that brings with it both changes to the efficiency and how effective it is,” he said.

Lisa Speer, director of the Natural Resources Defense Council’s International Oceans Program, also raised questions about OIF and its effectiveness for storing CO2 for the long term in an interview with GHG Monitor. “The maximum time these studies have been conducted has been a few weeks at best, and so one question is whether this actually works. Does the carbon actually stay down there and for how long, and is this truly sequestering carbon in an effective way?” she said. “There could also be unintended effects [such as] the possible creation of nitrous oxide, which is a much more potent greenhouse gas, and the largely unknown impacts on the ocean environment. We don’t know what the implications are for doing this in a very large area for a long period of time.”

Geoengineering, Including OIF, Remains Highly Controversial

Regardless of this particular project’s results, whether or not researchers will be able to continue studying the topic of OIF outside of the lab remains unseen. Often classified among the geoengineering techniques seen as last-resort efforts to mitigate the effects of climate change, OIF is still considered highly controversial and faces relatively high levels of political opposition. In 2007, after the researchers on this particular study began their work, 191 parties to the U.N. Convention on Biological Diversity issued a statement of concern surrounding OIF, calling for a moratorium on all large-scale operations aside from very basic research. Ever since, very few projects have gotten the greenlight to move ahead. Speer said she does not think that any more projects will get political support moving forward. “If they think they’re going to have trouble in getting CCS to work or reduction of emissions to work, I think they’re going to face an equally steep hill in convincing people that it’s worth sort of gambling with the ocean and I think that seems to me to be a very important question,” she said.

Smetacek and Buesseler both said that more research is needed to ultimately see if OIF is a potential option for climate change mitigation. “We know that iron itself is not a toxic thing that we’re putting into the ocean. So I think if people just step back and allow this research to go forward, if anything, if you’re against ocean iron fertilization this might give you the information to say that this might not be a good idea,” Buesseler said. “But let’s get the information, let’s get the numbers to either regulate this at some level or not allow it and then move on to the next, and that seems like it’s kind of the merit of this type of study.”

OIF Not a Silver Bullet, Researchers Agree

Even if work somehow can move forward and widespread commercial OIF operations commence, it cannot be the “silver bullet” for climate change given that at most it can store a fraction of the 9 gigatonnes of annual global emissions, Buesseler said in his commentary. “The ocean’s capacity for carbon sequestration in low-iron regions is just a frac¬tion of anthropogenic CO2 emissions, and such sequestration is not permanent—it lasts only for decades to centuries,” he said in his commentary piece. “However, humans have already embarked on an ocean geoengineering experiment through our energy practices (which are affecting climate and acidifying the seas), by fishing, and through our other uses of ocean resources.”

While OIF should be a method of last resort, Klaas said, it should still be pursued. “We need to face the reality here that not much is being done at the moment, so I think that we have to do research at least,” she said. But Speer disagreed. She classified OIF as a “distraction” from other, more tried, methods to mitigate climate change.  “There is a huge rang of uncertainties out there,” she said. “In contrast, we know what does work. We know that reducing emissions works. We know that carbon capture and storage works. One of the concerns is that by pursing these sort of schemes, we’re putting off taking on the action that’s really necessary to deal with greenhouse gas emissions.”