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Artificial ocean fertilization

This article introduces Artificial ocean fertilization as a possible route to large-scale atmospheric carbon dioxide removal.
© Ben Murphy, University of Glasgow
  • Babakhani, P., Phenrat, T., Baalousha, M., Soratana, K., Peacock, C.L., Twining, B.S., Hochella, J., Michael F & Pacific Northwest National Lab. (PNNL), Richland, WA (United States) 2022, “Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal”, Nature Nanotechnology, vol. 17, no. 12, pp. 1342-1351.
  • “Using engineered nanoparticles to increase carbon dioxide storage in the ocean”, 2022, Nature nanotechnology, vol. 17, no. 12, pp. 1245-1246.
  • https://ioc.unesco.org/our-work/blue-carbon 

As we have learnt, there is an urgent need to remove CO2 from the earth’s atmosphere. Time is running out for society to re-balance the Earth’s energy systems. We have looked at a couple of possible avenues through which CO2 removal can be achieved such as tree planting. We have also learnt about the complexities of nature-based solutions and how they have to be carefully implemented in order to be effective. 

As well as land-based ‘green’ solutions, there have also been a number of ‘blue’ solutions and possibilities for CO2 capture and removal. As the world’s biggest carbon sink, our oceans and coasts are essential to efforts to tackle the climate crisis. ‘Blue carbon’ projects include efforts to protect and restore marine ecosystems such as coastlines, tidal marshes and sea grasses, and mangroves. Blue carbon has significant potential to help reduce CO2 levels in the atmosphere whilst protecting and enhancing the world’s oceanic ecosystems.

The term “blue carbon” refers to the carbon stored in coastal and marine ecosystems. The so-called blue carbon ecosystems – mangroves, tidal and salt marshes, and seagrasses – are highly productive coastal ecosystems that are particularly important for their capacity to store carbon within the plants and in the sediments below. Scientific assessments show that they can sequester two to four times more carbon than terrestrial forests and are thereby considered a key component of nature-based solutions to climate change (UNESCO). 

The coastal ecosystems of mangroves, tidal marshes, and seagrass meadows provide numerous benefits and services that are essential for climate change adaptation along coasts globally, including protection from storms and sea level rise, prevention of shoreline erosion, regulation of coastal water quality, provision of habitat for commercially important fisheries and endangered marine species, and food security for many coastal communities. Additionally, these ecosystems sequester and store significant amounts of coastal blue carbon from the atmosphere and ocean and hence are now recognized for their role in mitigating climate change.

Whilst blue carbon showed early potential in terms of both off-setting and direct carbon capture, it has taken several years to reach the point today where we have a body of evidence to support any possible implementations of blue solutions.

Despite these benefits and services, coastal blue carbon ecosystems are some of the most threatened ecosystems on Earth, with an estimated 340,000 to 980,000 hectares being destroyed each year. It is estimated that up to 67% and at least 35% and 29% of the global coverage of mangroves tidal marshes and seagrass meadows respectively have been lost. If these trends continue at current rates, a further 30–40% of tidal marshes and seagrasses and nearly all unprotected mangroves could be lost in the next 100 years. When degraded or lost, these ecosystems can become significant sources of greenhouse gas carbon dioxide (The Blue Carbon Initiative). 

As well as restoration and protection, other ocean-based climate solutions are in scientific development. One of these is natural ocean fertilization. Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean.

In a recent paper, Babakhani and colleagues (Babakhani et al., 2022) examined the scientific evidence for seeding the oceans with iron-rich engineered fertilizer particles near ocean plankton. The goal would be to feed phytoplankton, microscopic plants that are a key part of the ocean ecosystem, to encourage growth and carbon dioxide (CO2) uptake.

To remove carbon dioxide from the atmosphere, artificial ocean fertilization (AOF) intentionally adds a limiting nutrient (typically iron) to stimulate phytoplankton growth and CO2 uptake in the oceans (Fig. 1a). A fraction of the stimulated phytoplankton biomass subsequently sinks, exporting carbon to the deep ocean and potentially the ocean.

Concept of Artificial ocean fertilization

In their analysis, the researchers argue that engineered nanoparticles offer several attractive attributes. They could be highly controlled and specifically tuned for different ocean environments. Surface coatings could help the particles attach to plankton. Some particles also have light-absorbing properties, allowing plankton to consume and use more CO2. The general approach could also be tuned to meet the needs of specific ocean environments. For example, one region might benefit most from iron-based particles, while silicon-based particles may be most effective elsewhere, they say.

The researchers’ analysis of 123 published studies showed that numerous non-toxic metal-oxygen materials could safely enhance plankton growth. The stability, Earth abundance, and ease of creation of these materials make them viable options as plankton fertilizers, they argue.

In their novel study, the authors note that although ENPs show promise in addressing many of the current AOF limitations such as bioavailability, nutrient/light co-limitation, phytoplankton bloom longevity and carbon export efficiency, present information and estimations are based on diverse contexts rather than focused studies on the use of ENPs in realistic AOF conditions. There remain 3 key challenges in overcoming public and regulatory concerns:

  1.  The potential toxicity of ENPs to marine ecosystems under realistic conditions. 
  2. The unknown long-term impacts of ENP additions on the biogeochemistry of the oceans. 
  3. The tendency of ENPs to aggregate over time within the marine environment.

The team also analyzed the cost of creating and distributing different particles. While the process would be substantially more expensive than adding non-engineered materials, it would also be significantly more effective. 

© Ben Murphy, University of Glasgow
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