- Artificial upwelling is a form of geoengineering that aims to use pipes and pumps to channel cool, nutrient-rich water from the deep ocean to the surface. In doing so, it could fertilize surface waters, prompting the growth of plankton, which can then absorb and store large amounts of atmospheric carbon.
- Long considered a potential marine carbon dioxide removal (CDR) method, artificial upwelling has more recently been coupled with seaweed farming to potentially soak up even more atmospheric CO2.
- But technological challenges have plagued open-water upwelling experiments, while environmentalists worry that large-scale use could ultimately prove ineffective and ecologically harmful.
- Experts state that though upwelling could prove a viable solution to improve fisheries and protect coral reefs from marine heat waves, more research is needed. Considering the rapid current pace of climate change, it’s debatable as to whether implementation at scale could come in time to stave off dangerous warming.
Artificial upwelling is a geoengineering climate solution with a long history. The concept: mimic natural ocean upwelling by pumping cold, nutrient-rich seawater up from ocean depths via pipes to the surface.
There it can cause a growth surge in CO2-absorbing plankton, nourishing aquaculture and tackling climate change. Closer to shore, the technique could even protect coral reefs from marine heat waves.
But as simple as this idea sounds in theory, it has faced complex technological challenges, high costs and failed experiments, though it continues to garner interest. Whether marine upwelling will ever break through as a solution for fisheries or the climate is unclear.
Upwelling isn’t a new idea. First proposed in the 1970s as a method to feed fish farms and grow seaweed, it has seen waves of testing come and go.
Over past decades, trials have operated with mixed success. In 2008, one test near Hawai‘i pumped cold, nutrient-rich water from a depth of 300 meters (nearly 1,000 feet). But that trial lasted just 17 hours before the pump failed. By contrast, tests in a semi-closed embayment in Aoshan Bay, China, between 2018 and 2020, proved more successful in prompting macroalgae growth.
Starting in the 1990s, artificial upwelling was proposed as a way of propagating vast floating seaweed farms, spurring CO2 uptake as a climate solution. It’s also seen as a potential way of saving coral reefs from devastating heat wave-induced bleaching events.
But putting all this theory fully into practice, even in small-scale experiments, has proven difficult, while scaling up remains a far future prospect, say critics.
Climate potential and technological challenges
As already mentioned, a primary artificial upwelling technique proposes pumping cold, nutrient-rich water up from the ocean floor to fertilize surface waters in nutrient-poor ocean zones to spur the growth of marine life that can absorb atmospheric CO2.
Another approach uses artificial upwelling to feed massive seaweed farms, which could lock up carbon. The seaweed could then be harvested for biofuel and biofertilizer, or be sunk back to the sea bottom, sequestering carbon.
That latter approach is the vision of Seafields, a company that hopes to capture and farm sargassum seaweed as a climate solution. As global warming escalates, sargassum has become a detriment to tourism and public health in the Caribbean, as the ocean weed proliferates in warm seas, is washed up on beaches, and dies there and rots in stinking heaps.
Artificial upwelling is seen as a way of transforming that headache into an entrepreneurial climate solution. But developing the technology to do so seems far off, even for company director John Auckland.
Still, “If you want to grow these [sargassum] farms very quickly, [you’ll be] growing them in nutrient-deprived waters. So artificial upwelling is a way of doing it,” Auckland says. But “I actually, personally, don’t think it’s the best way of doing it. I don’t think hundreds of thousands of pipes in the ocean is practical, or good for marine life.”
Seafields planned and raised funding for an on-land artificial upwelling test facility, but that fell through. “We were never able to execute on that test because it’s just too big an engineering challenge,” Auckland notes, adding that this failure is “a bit … ominous.” The firm’s next step is to use currently available pumping technology to gauge whether artificial upwelling is even necessary to grow sargassum.
Aside from making pumps work, costs pose a major barrier, ranging from $100,000 to $1 million per pipe, Seafields says. Each pipe needs to run to around 400 m (about 1,300 ft) deep, and there’s still uncertainty how many would be needed to feed the seaweed.
“Do we need 400,000 of these pipes, or do we need 4 million to get to a gigaton of CO2 removal?” Aukland wonders. “So, we’ve also got an order-of-magnitude range there, which is problematic.”
Disappointing trials
A small-scale test conducted off the Canary Islands is emblematic of the technological challenges plaguing artificial upwelling. That project, dubbed Test-artUP, ran between 2021 and 2024. Funded by the German Ministry of Education and Research, it aimed to study the effects of a single artificial upwelling pump device running for several weeks.
Ultimately, it was a “big disappointment,” says Michael Sswat, a postdoctoral researcher at the GEOMAR Helmholtz Centre for Ocean Research in Germany, who was part of the study team. After momentary success, the device sputtered to a halt after just four hours of operation.
“With the current state of technology available for artificial upwelling, it is probably not viable, because there’s such a tremendous amount of research that still has to go into the technical side of things,” Sswat says.
Despite such setbacks, Brian von Herzen, CEO of the Climate Foundation, says artificial upwelling could be viable for ecological restoration — needed due to climate change-induced surface warming and ocean stratification, which can stall life-giving natural upwelling and sea surface fertilization. For that reason, von Hersen uses the term “restoring natural upwelling” instead of artificial upwelling.
His organization is now trialing a different approach: a deep-water cycling technique that moves seaweed from the surface to deep water. This is being done in part to avoid the controversial biodiversity impacts of standard upwelling methods, which raise concerns of eutrophication and other environmental impacts.
Based on this test, deep cycling could be highly effective for seaweed growth, but less so when it comes to restoring fish populations. Though von Herzen’s organization doesn’t plan to pursue upwelling, he offers that: “We would be happy to support the trialing at appropriate scale of restoring natural upwelling, because without it, many ecosystems will perish.”
Upscaling uncertainty and dangers
Experts underline that artificial upwelling has never been fully accomplished on more than a small scale, so upscaling comes laden with uncertainties. One major unknown: Will upwelling actually work as a method for carbon dioxide removal, or CDR?
Research by David Koweek, chief scientist at Ocean Visions, suggests that even if tech challenges are overcome, the CDR efficiency of artificial upwelling is limited and unlikely to reach the much-hoped-for gigaton scale — more likely it will top out at around 100 megatons of carbon storage annually, he says.
“When you pump up deep ocean water, it’s full of nutrients, but it’s full of carbon dioxide too, and basically it’s full of as much carbon dioxide, more or less, as we think could be captured by plankton or seaweed,” Koweek says. “You’re kind of just running on a treadmill.”
Modeling studies, led by Malte Jürchott, a researcher at the GEOMAR Helmholtz Centre for Ocean Research, found that artificial upwelling is only effective when combined with ocean iron fertilization. That’s a controversial geoengineering technique whose research is currently hampered by restrictive regulations.
Another of Jürchott’s papers indicates that artificial upwelling could become more effective with future higher concentrations of CO2 in the atmosphere. But, of course, a high-emissions scenario is “undesirable for humanity for various reasons,” Jürchott says. So, this increased potential shouldn’t be viewed as “an excuse to continue to emit large amounts of CO2 into the atmosphere.”
Ocean upwelling also has a monitoring problem: It’s difficult to accurately measure and account for CO2 removed from the atmosphere, unlike some other geoengineering approaches, such as electrochemical CDR, say experts.
Others worry that upwelling in one part of the ocean could lead to changes in fishery productivity elsewhere, raising governance and food security concerns.
More troubling, the technique could disrupt the ocean heat budget. Once artificial upwelling is initiated en masse with thousands of pumps funneling deep water to the surface, it can’t be safely stopped, says Jürchott. That’s because pumping cold water to the surface traps more heat in subsurface waters. When stopped, that heat transfer ends but the energy must go somewhere, eventually returning to the surface and warming the Earth.
That’s a major concern for Lennart Bach, a University of Tasmania researcher. “It’s not the horse I would bet on in this whole marine carbon removal space, because it’s extremely complex,” he says. With upwelling, “Ocean physics are manipulated to change ocean chemistry in order to hope that ocean biology does what you want.”
Joaquin Ortiz, who carried out his Ph.D. research on artificial upwelling and is now head of research at MacroCarbon, a seaweed farming startup, says artificial upwelling’s potential lies in “food web enhancement” rather than CDR. For him, that could also overcome the problem of scaling up the tech.
That’s a view shared by the U.S. National Academy of Sciences. In a 2022 report, that body wrote that even millions of artificial upwelling pumps operating across the oceans “would not meet CDR goals for [carbon] sequestration or permanence.” But they could “prove to be a valuable tool to promote aquaculture or fisheries.”
Recent research in the Gulf of Maine may support this claim. Researchers there successfully tested a wave-powered pump in shallow waters 50 m (164 ft) deep.
According to Chelsea Kimball, a Ph.D. student at the University of New Hampshire, upwelling could help a budding kelp industry in New England, while minimizing some of the concerns of pumping up deep ocean water, she says, though more studies are underway. “Our approach is to use [the technology] with macroalgae, but it could also be used for fish aquaculture, keeping fish cool in the summer,” potentially vital as ocean heat waves become more common and deadly.
Other researchers have proposed artificial downwelling — essentially the reverse process, funneling surface water saturated with CO2 down to the ocean floor for long-term storage. Experts note that downwelling occurs to an extent when upwelling is carried out, but a specific focus on downwelling methods has received little attention.
That’s because it would be an inherently expensive and likely inefficient means of storing carbon dioxide, says Koweek. In his view, downwelling could be more effective as a means to counteract hypoxia in deoxygenated waters. But that idea has also garnered little interest.
Holding coral bleaching at bay?
Just as natural upwelling creates vibrant ecosystems, it could also offer coral reefs protection from climate change. In a 2024 paper, researchers showed how parts of Australia’s Great Barrier Reef are buffered against marine heat waves thanks to natural upwelling. Building on this knowledge, scientists and conservationists are exploring the use of artificial upwelling to mimic naturally generating refugia.
Yvonne Sawall, a marine ecologist at Arizona State University, is leading research at the Bermuda Marine Mesocosm Facility to better understand this process with the hopes of doing field tests.
“If we can create these thermal refugia in the reef, and we impose strong temperature fluctuations created by artificial upwelling, we can hopefully increase the heat tolerance of the corals within those refugia,” she says. “So, when corals die around those refugia, those corals can reseed the depleted reef environments.”
Lab results so far show that bleaching is slowed. But there are concerns that bringing up deep water in open ocean could change nutrient levels, leading to eutrophication or altering surface pH. Such changes could spell bad news for balanced coral reefs. Sawall says her team’s method would only use pulses of cold deep water, rather than continuous flows, resulting in minimal changes in surface nutrients and pH.
“In my opinion, it would definitely be effective,” she says. But again, the technological challenges and questions of scale come to the fore. “It’s proven that, of course, once you bring cold water to the surface, it will definitely benefit the corals. It’s just the implementation isn’t easy.”
Sawall envisages subjecting only small pockets of a reef to artificial upwelling. “It’s [technologically] impossible to do this for an entire reef system,” she says.
It’s a strategy also considered by the Australian Reef Restoration and Adaptation Program (RRAP), which is currently trialing several reef-protection methods, including marine cloud brightening.
“Our conclusion was that this could be of value in very localized and specific circumstances, but not scalable for larger systems such as the Great Barrier Reef, due to infrastructure needs and deployment costs,” RRAP executive director Cedric Robillot wrote in an email.
“Ecological risks associated with bringing nutrient rich water to the surface layers should also be considered,” he added. “We are always looking for updates to the state of the art, but so far have not seen any radical technology improvement that would make these approaches viable on a large scale.”
A questionable future
A fundamental problem, agree experts, is that scaling up artificial upwelling is fraught with technological complexities and environmental risks. Despite that, upwelling remains on the radar, for now, but opinions are mixed as to whether it will ever be viable. The University of Tasmania’s Bach, for example, says: “It would be very low on my list of receiving funding. So for me, currently, it’s a non-starter.”
Others say deploying artificial upwelling at smaller scales for targeted purposes could be beneficial. Ortiz, from seaweed farming startup MacroCarbon, says upwelling should remain a “high priority” for fisheries as “it’s much simpler on that scale.”
Regarding reefs, Sawall plans to conduct a coral community experiment, extending her lab trials beyond a single coral species. “It’s still in the mesocosm,” she emphasizes. “It’s not outdoors, because I don’t even want to think about the whole permitting stress.”
If Sawall’s team can show that artificial upwelling has minimal negative effects in the lab, then the next step would be small-scale field experiments, she says, with community buy-in.
“I don’t see myself as someone who is necessarily advocating for this kind of intervention,” she explains. But in her view, there’s a dire need for effective strategies to reduce marine heat waves. “I’m really relying on the results we get from the experiments. I’m not saying that this is the solution we should definitely use, but I think it’s something conservationists should have in their toolbox.”
A final hurdle: Poor results thus far have resulted in a funding drought, notes Koweek. “Until [sufficient funding] happens, we’re going to be … stuck in this loop where people think [upwelling] has some potential, but nobody’s really looked at it, and so therefore, nobody can justify the investment of resources to look at it further.”
Banner image: Nontoxic dye released from an artificial upwelling experiment off the Canary Islands. That experiment, set to last weeks, ended after just one day when the pump failed. “To most of us that proved … the technical readiness of this approach is not there,” says Michael Sswat, a postdoctoral researcher at GEOMAR Helmholtz Centre for Ocean Research, who was part of the research team. Image courtesy of Michael Sswat.
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