Key points
- Ocean alkalinity enhancement, or OAE for short, has emerged as one possible solution for Australia in tackling carbon dioxide removal.
- Elevating the ocean's pH may help it to act like a sponge and absorb more atmospheric carbon dioxide.
- Genomics-based approaches may help to resolve key uncertainties which remain around the environmental impacts of changing ocean pH.
What if one of the solutions for climate change were to boost the storage capacity of the ocean?
That's what a new area of science called ocean alkalinity enhancement (OAE) promises.
It's a solution inspired by nature – where seawater absorbs carbon dioxide (CO2). Over vast time spans, CO2 dissolves into the ocean. It's then permanently stored away as carbonate ions.
The transfer of CO2 from the atmosphere into the depths of the ocean can take centuries, but OAE could accelerate this process.
There is more than one way to add alkalinity to the ocean. It can be done using electrochemistry to split seawater into acidic and basic components. Another way is adding alkaline minerals.
Both OAE methods lead to the same outcome. Adding alkalinity elevates the pH, causing a shift in the carbonate system in seawater. This results in additional uptake of CO2 from the atmosphere.
OAE is gaining momentum in countries like the US, Canada, and more recently, Australia. It could help remove excess carbon dioxide from the atmosphere and rebalance the carbon cycle. It could also counteract ocean acidification.
It’s an enticing solution. But can’t we just plant more trees?
We need new carbon solutions
Not really. Here's why.
Trees, soils and the ocean all play an essential role in abating climate change. They do this by sequestering atmospheric carbon dioxide.
Today, CO2 is accumulating in the atmosphere at an unprecedented rate.
In response, most nations, including Australia, are looking at reducing and removing greenhouse gas emissions as quickly as possible.
Many of the ways to remove carbon dioxide are familiar to us.
These include planting trees, managing soils, or restoring mangroves or kelp forests. Unfortunately, there isn’t enough room in these carbon sinks to store the amount of carbon dioxide required to limit global temperature increases to under the Paris Agreement target of 2 degrees.
There’s also the issue of permanence. Bushfires and other catastrophes can release stored carbon back to the atmosphere.
The international consensus is now clear that reducing emissions is no longer sufficient to limit warming increases to under 2 degrees. We now need to remove carbon dioxide durably from the atmosphere and store it away for long time periods.
This means a raft of new solutions, including adding crushed rocks and microbes to soils, installing large vacuum machines on land, and OAE are now needed.
We must deploy these technologies fast and at scale to prevent serious risks.
What are the risks of OAE?
As marine scientists and communicators, we’re the first to advocate for the health of our oceans. That includes ensuring that climate solutions do not have greater risks than benefits.
Because it involves adding materials to the ocean, OAE is not without its complexities.
One concern is around marine ecosystems. With the known consequences of ocean acidification on marine life, there is concern that elevating pH may have equivalent impacts on marine ecosystems.
Tiny marine plants called phytoplankton photosynthesise – just like plants on land – and generate oxygen. They do a lot of heavy lifting when it comes to contributing the oxygen in the air we breathe.
On the other hand, alkalinity enhancement (lowering acidity) could benefit shell-forming organisms, like oysters and scallops. But subtle changes to the pH could have unintended side effects.
Why use genomics?
We must ensure OAE can be deployed in a safe and transparent way. And we must be certain that any approaches we use have known and tolerable environmental consequences.
Experiments in the field can help us measure for impacts, including those that we may not have originally accounted for. This includes understanding which types of phytoplankton are in the ocean, and what ocean conditions are present.
But we need to go further. We need to be able to verify what is happening at a microscopic level. Our decades-long research into genomics could play a significant role in closing knowledge gaps.
Genomics is the study of genetic material (DNA and RNA) collected from samples. We’re interested in samples from phytoplankton and other microorganisms (known collectively as ‘plankton’). These make up the base of the ocean food chain.
Why use plankton for ecosystem monitoring?
Plankton may be small, but they play a huge role in ecosystem health. They are sensitive to disturbance but quick to recover. So, if we measure a disturbance at this level in the ecosystem using genomics, we can quickly stop OAE experiments to prevent more widespread ecosystem-level changes.
Two of these new monitoring technologies could help in understanding the risks and opportunities of OAE.
- Metabarcoding: we can use common genes in the plankton’s DNA to create a name tag ID. This approach tells us which plankton are present and abundant in a water sample. This means if a sensitive organism were to diminish or disappear, we would be able to tell.
- Metatranscriptomics: we can measure all the RNA in a sample of seawater. This allows us to tell what physiological processes the plankton are carrying out at the time.
Using these tools would let us know if the small changes in pH would lead to big changes in the metabolic capacity of the plankton. They would also tell us how big the changes would be and over what scale. This would allow us to predict if other animals in the ecosystem would be affected.
What does this mean for future OAE research?
It's important to remember that genomics provides just one line of evidence to ensure that OAE approaches are safe and effective.
We don’t have all the answers to make a call on OAE just yet. But we're certain OAE warrants further investigation.
Large-scale modelling simulations have already shown OAE to be effective, but we still need to determine whether it is a potentially viable CDR option for Australia. If OAE progresses to large-scale deployments, it will require robust and safe methodologies.
Our research has helped provide a tool to assess environmental impacts of OAE. Genomics could provide essential guardrails to protect our marine ecosystems.
Ultimately, OAE technologies in development will need to be modified and adjusted in response to emerging research like ours to ensure that they are developed responsibly and safely and deliver a net positive benefit to our planet.