Is ocean iron fertilization back from the dead as a CO₂ removal tool?
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Is ocean iron fertilization back from the dead as a CO₂ removal tool?by Jeremy Hance on 14 November 2023
- After a hiatus of more than 10 years, a new round of research into ocean iron fertilization is set to begin, with scientists saying the controversial geoengineering approach has the potential to remove “gigatons per year” of carbon dioxide from Earth’s atmosphere.
- The idea behind ocean iron fertilization is that dumping iron into parts of the ocean where it’s scarce could spark massive blooms of phytoplankton, which, when they die, can sink to the bottom of the sea, carrying the CO₂ absorbed during photosynthesis to be sequestered in the seabed for decades to millennia.
- So far, proof that this could work as a climate-change solution has remained elusive, while questions abound over its potential ecological impacts.
- Scientists with the Woods Hole Oceanographic Institution in Massachusetts, U.S., recently received $2 million in funding from the U.S. government that will enable computer modeling research that could pave the way for eventual in-ocean testing, effectively reviving research into ocean iron fertilization.
In 2009, a controversial scientific experiment dumped 6 metric tons of dissolved iron into the Southern Ocean to see if it would trigger a massive bloom of phytoplankton in iron-deficient waters. In one way, the experiment succeeded: The scientists produced a phytoplankton bloom. However, they didn’t get what they were really after: Proof that such a scheme could lead to large-scale carbon dioxide sequestration. You see, when phytoplankton die, they sometimes sink to the bottom of the sea — a phenomenon known as marine snow — carrying the carbon dioxide they absorbed during photosynthesis with them to be sequestered in the seabed for decades to millennia. In 2009, the vast majority of the experimental bloom was consumed by zooplankton near the surface and failed to reach the ocean floor.
Since then, except for an even more controversial attempt by a for-profit company in 2012 in Canadian waters, there have been no large-scale experiments of ocean iron fertilization as a potential tool to counteract climate change.
Now, researchers hope to change that. Dennis McGillicuddy and Ken Buesseler, both with the Woods Hole Oceanographic Institution in Massachusetts, U.S., have a multistage project in mind that Buesseler says would be about “10 times longer [and] 10 times bigger” than any past experiment. They say they hope such a scaled-up experiment will answer many of the questions that still remain about the efficacy of ocean iron fertilization.
McGillicuddy says iron fertilization remains intriguing because it has the potential to store “gigatons per year” of carbon dioxide.
“It doesn’t solve the problem by any stretch, but that’s an amount of carbon that is meaningful from a climate perspective,” he says.
Recently, they scored their first grant to bring iron fertilization experiments back. In September, the U.S. National Oceanic and Atmospheric Administration’s (NOAA) Ocean Acidification Program announced $2 million in federal funding for a computer modeling project, part of a $24.3 million funding package for a suite of marine CO2 removal studies.The modeling won’t involve any in-ocean experiments, but it’s the first step to trying iron fertilization experiments again.
Since the last experiment in 2009, Earth’s climate has only grown hotter and more unstable. This year looks to be the warmest on record (again) and may end up being the warmest in more than 100,000 years. Our planet has been rocked by record fires, floods and droughts due to climate change and El Niño conditions this year alone. Rates of warming and ice melt in Antarctica have surprised even the most seasoned scientists. All this has prompted researchers to look more intently at potential methods to sequester massive amounts of CO2.
“There’s a lot of legacy carbon that will have to be removed from the atmosphere,” says Gregory Frost, a climate expert with NOAA. “I would say it’s a scientific consensus statement that some form of carbon removal will be needed to remove that legacy carbon.”
The big idea
The core of our planet is made almost entirely of iron, making it — and not oxygen — Earth’s most common element. But that doesn’t mean iron is abundant everywhere. There are areas of the ocean where iron remains quite rare. Past research has shown that iron enters the ocean through dust blown on the winds from land or inflow from rivers. In remoter parts of the ocean, such as the Southern Ocean, the central Pacific, or the Arctic Pacific, iron is a rare commodity.
This matters because iron is indispensable for photosynthesis, the process underpinning most of our planet’s wild and verdant life. In iron-depleted seas, it is iron — not sunshine or heat or nutrients like nitrogen and phosphorous — that’s holding phytoplankton back. Phytoplankton suck carbon out of the atmosphere during respiration, and when they die under the right conditions, they can take that CO2 to the bottom of the sea with them.
In the late 1980s, oceanographer John Martin first hypothesized that adding more iron to the ocean could lead to the ocean sequestering more carbon, famously opining, “Give me a half tanker of iron, and I will give you an ice age.”
But real-world tests from the late 1990s up to 2009 showed it wasn’t quite that simple. First, researchers had to figure out where iron was rare in the oceans. Then they had to see if they could create phytoplankton blooms there by adding iron experimentally. And then they had to show that that iron fertilization actually led to sequestration of carbon.It’s fair to say these past experiments left a murky picture. They certainly identified iron-depleted parts of the ocean and showed iron fertilization could spark blooms. But whether the blooms fell to the seabed and sequestered CO2, or for how long, remained open questions, largely because the experiments were not well-designed to test those points. Controversy around several of the tests didn’t help matters, effectively ending experiments for more than a decade.
“The gap was largely, in my opinion, due to negative pressure by some special interest groups concerned about ‘geoengineering’ in general, and some of the bad behavior at that time from Planktos and other commercial efforts done in a nonscientific way,” says Buesseler. Planktos was a for-profit company that drew controversy over a plan to dump iron in the sea near Ecuador’s famed Galápagos Islands, but ran out of funding before it could do so.
But, according to a NOAA special report from May, iron fertilization still shows promise. Moderate promise, anyway: NOAA rated iron fertilization as having low-to-moderate potential for cost, scalability and how long carbon might be stored compared to other marine sequestration ideas. Still, that’s enough to pique the agency’s interest in garnering more research.
“The overarching goal was really to fund research that looks at the different marine carbon dioxide removal approaches, their inherent risks, but also potential co-benefits,” says Gabby Kitch, a marine geochemist with NOAA and co-author of the special report who was involved in selecting projects for funding. “This project fell to the top of those that were technically sound.”
Ten times larger and longer
The $2 million in funding will allow researchers, led by McGillicuddy, to bring more robust modeling to iron fertilization. McGillicuddy says this will involve “observing system simulation experiments” to figure out the best ways to measure both the carbon sequestration potential for iron fertilization as well as any impacts on ecosystems.
“There’s still a lot of uncertainty in the iron cycle in the ocean, for example. Therefore, we need … an ensemble of these models to inform our decisions,” McGillicuddy says.
The next steps, not included in current funding nor set to launch anytime soon, would be designing in-field experiments that build on the modeling work, potentially larger ones with longer time frames than any past experiment.
“I think we could be out there in 2025 if we could get the resources 12-plus months beforehand,” Buesseler says of an actual field test. “Now that’s about twice as fast as a normal planned experiment, but there’s some urgency here. We think we have technology to do it [in] much, much better ways” than previous experiments.
Buesseler and McGillicuddy are currently eyeing some areas in the northern Pacific, off Alaska or Canada, where the water is relatively calm for a first test site. Buesseler says three months of monitoring using autonomous vehicles and satellite imagery could provide a longer data set and time frame than past experiments, including real-time data on several parameters. It should pick up any ecological impacts, such as disrupting wildlife, toxic algae blooms or dead zones.
But he adds, “I want to be out there for the entire year and maybe do this a couple of times and come back the next year.”
After that, the team hopes to do similar field studies in other regions, including the Southern Ocean, which has the biggest potential for iron fertilization.
Buesseler and McGillicuddy note that their team will be following all rules and regulations. “This is an international consortium of scientists who are absolutely committed to openness and transparency with regard to all of the data sets that are collected,” McGillicuddy says.“We don’t want to be lumped in the same category as the pirates out there,” Buesseler adds, referring to past projects operated by for-profit entities that lacked proof-of-concept or real-time data.
The scientific team also hopes to answer another long-term question: Will deploying iron fertilization in one part of the ocean affect nutrients like nitrogen and phosphorous elsewhere?
Modeling research published in 2020, led by Jonathan Lauderdale, an oceanographer with the Massachusetts Institute of Technology (MIT), predicts it will. Specifically, it suggests that the phytoplankton blooms resulting from more iron dumped in the Southern Ocean could gobble up nutrients like nitrogen and phosphorous that would otherwise eventually circulate to other parts of the ocean and support blooms there. The upshot could be more blooms in the Southern Ocean, but fewer blooms elsewhere, potentially resulting in a wash for the climate but major disruption for food chains.
Still, Lauderdale says he supports further research on iron fertilization though he adds he worries “that some for-profit companies might go ‘all in’ on iron fertilization” before these questions are answered.
Indeed, McGillicuddy says it would take two to three decades before scientists would know whether iron fertilization in one part of the ocean is robbing nutrients from another part. This is because the currents take decades to complete their cycles.
The researchers also stress that ocean iron fertilization could never replace emissions reductions. Rather, if it works, it would be a requirement beyond even the most aggressive emission reductions, given all the carbon already in the atmosphere.
“There’s no single one of these carbon dioxide removal strategies … that’s going to fix everything. They’re all a piece of the puzzle,” McGillicuddy says. “Nearly all have the potential for intended consequences, but also unintended consequences. From my perspective, all these strategies need to be vetted.”
When it comes to iron fertilization, the vetting process will soon begin anew.
Citations:
Lauderdale, J. M., Braakman, R., Forget, G., Dutkiewicz, S., & Follows, M. J. (2020). Microbial feedbacks optimize ocean iron availability. Proceedings of the National Academy of Sciences, 117(9), 4842-4849. doi:10.1073/pnas.1917277117
Martin, P., Van der Loeff, M. R., Cassar, N., Vandromme, P., D’Ovidio, F., Stemmann, L., … Naqvi, S. W. (2013), Iron fertilization enhanced net community production but not downward particle flux during the Southern Ocean iron fertilization experiment LOHAFEX. Global Biogeochemical Cycles, 27(3), 871-881. doi:10.1002/gbc.20077