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The challenge

Enhancing the ocean's natural alkalinity cycle

Currently, there are very high levels of carbon dioxide (CO2) in the atmosphere. This is a result of human activities, primarily the burning of fossil fuels, that result in the heat-trapping gas lingering in the atmosphere for up to hundreds of years. We need to explore ways to actively remove CO2 from the atmosphere in order to stabilise Earth's temperature.

Researchers are looking at a range of climate mitigation options. One of these potentially involves using the ocean to sequester some of the additional CO2 that has been emitted to the atmosphere. The ocean is already the largest reservoir of CO2 on the planet. It has the potential to store even more.

Some of challenges for the research community investigating ocean alkalinity enhancement (OAE) as one possible carbon dioxide removal technology (CDR) is whether it is possible to enhance the ocean's natural alkalinity cycle to work on much faster timescales (years to decades), and whether it can be done safely and responsibly.

[Music plays and a split circle appears and photos of different CSIRO activities flash through in either side of the circle and then the circle morphs into the CSIRO logo]

[Image changes to show the camera panning over the ocean, and text appears: Carbonlock- Research Project Spotlight, Ocean Alkalinity Enhancement

[Images move through to show Dr Elizabeth Shadwick talking to the camera, underwater view of fish swimming around, and an aerial view of camera panning over the ocean and land, and text appears: Dr Elizabeth Shadwick, CSIRO

Elizabeth Shadwick: I am Dr. Elizabeth Shadwick. I am a chemical oceanographer, and my research is focused on observing and understanding the ways in which the ocean exchanges carbon dioxide, or CO2, with the atmosphere.

[Images move through to show the Earth, a view from above the clouds, waves breaking and coming towards the camera, and then various underwater views of a diver and fish]

Net removal of carbon dioxide from the atmosphere requires both capturing it, so getting it out of the atmosphere, and also storing it somewhere over long periods of time. And the ocean has emerged as one of the feasible places where we could potentially store additional CO2 over long time periods.

[Images move through to show the camera panning through rocks underwater, over a boat moving across the ocean at sunrise, and then panning in to the waves trapped between rocks of a blowhole

The ocean is by far the largest reservoir of carbon on the planet in the present day. It already contains some 45 times more carbon dioxide than what is currently in the atmosphere.

[Image changes to show a medium view of Elizabeth talking to the camera, and then a close view of Elizabeth talking to the camera]

Rocks are input to the ocean and those allow the waters to become more basic or more alkaline, which induces an uptake of CO2 from the atmosphere

[Images move through to show an underwater view panning left showing waves hitting the rocks, panning through a deep underwater ravine, and then past various rocks]

And in fact, it's this process that occurs naturally in the ocean and allows CO2 to move from the atmospheric reservoir into the deep ocean, where it stays in a stable form for tens of thousands of years.

[Images move through to show a fish swimming into a cave, an oil refinery, a power plant, an aerial view of the power plant, logs stacked, a male using a cement mixer, and fish in an underwater cavern]

If we wait long enough the majority of anthropogenic CO2, so that's CO2 that has found its way into the atmosphere from human activities, those are burning of fossil fuels, deforestation, cement production, those CO2 emissions will ultimately end up in the ocean through natural processes.

[Images move through to show an underwater view looking up to the surface, camera panning in to the fish swimming around rocks, and then a diver swimming in a cave]

We would like to find technologies and strategies that allow us to forcefully accelerate the process of moving the CO2 into the ocean.

[Images move through to show various views of Elizabeth talking to the camera, an underwater view of fish swimming through kelp, and then fish swimming underwater]

We are focusing on studying something called ocean alkalinity addition, which is adding alkalinity or a basic material to the ocean to induce an additional uptake of CO2 from the atmosphere.

[Images move through to show waves crashing on rocks with blowholes, various views of Elizabeth talking to the camera, and then an aerial view of ocean waves]

What we are interested in doing is what we call electrochemical approaches, and that involves a first step of taking seawater and splitting it into its acidic and basic components, so that would be hydrochloric acid as the acid and sodium hydroxide as the base, and then reintroducing the basic component back to the ocean.

[Images move through to show an underwater view of a diver swimming with fish, rocks underwater, and then the glare of the sun’s reflection on the ocean]

The way that we will track this modified stream of seawater is using both in ocean state of the art sensors, some of which are being developed by our team and also really sophisticated biogeochemical ocean models.

[Images move through to show Dr Richard Matear talking to the camera, hands using a keyboard, and fish swimming around a reef, and text appears: Dr Richard Matear, CSIRO]

Richard Matear: I am Richard Matear. I am a climate scientist working at CSIRO. I have spent about three decades modelling the climate system, with a particular focus on the oceans and the role of the oceans in the climate and carbon cycle

[Images move through to show a close view of a supercomputer, waves washing into a beach, an underwater view of the ocean floor, and then a time lapse of a boat moving across the ocean at sunset\

With models, we can actually do this ocean alkalinity addition. We can track how it behaves in the ocean and we can also quantify how it's taking up carbon dioxide from the atmosphere.

[Images move through to show a camera view panning down underwater to the seaweed on ocean floor, and then a partial view of the Earth’s surface

So the models provide a nice kind of toolkit to first start that exploration and we have done that at global scales

[Images move through to show various views of rocky coastline, an aerial view looking towards the town, a time lapse of an ocean and land view, and then fish swimming past coral]

And as we push forward with this particular project, we'd like to do that at much more local and regional scales.

[Images move through to show waves rolling past as the camera pans out, fish swimming over coral, various views of Richard talking to the camera, and three squid swimming over seaweed]

This research is not advocating doing carbon dioxide removal, but really providing the fundamental science that allows us to make a critical assessment of whether this is a good idea or not.

Our research is really targeting can we have an effective way of removing carbon dioxide from the atmosphere? Can we do it in a way that actually doesn’t have any detrimental impacts on the biology of the ocean or the chemistry of the ocean?

[Images move through to show various views of Elizabeth talking to the camera, the power plant producing smoke, and the eye of an cyclone]

Elizabeth Shadwick: The idea that we should not tinker with the ocean is a really understandable place to be and earlier in my own career, I shared some of those reservations.

[Images move through to show aerial view of flattened trees, and then an aerial view of a flooded river]

I think now that the problem has become so much more urgent and we are really beyond the place where we can just rely on moving away from emissions we really need to do net removal as well.

[Images move through to show an aerial view of a fire engine moving beside burnt smoking ground, two kangaroos, and then various views of Elizabeth talking to the camera]

I think one way of helping people to understand the urgency is to think of the natural experiment that we are already all of us participating in, which is the release of fossil fuel emissions to the atmosphere.

[Images move through to show various views of power plants billowing smoke, and then fish swimming beside an anemone on rocks]

One could argue that's the biggest geoengineering experiment we have going and what we are talking about would actually help to reset the ocean to its pre-industrial conditions.

[Images move through to show an aerial view of a bushfire raging, an aerial view of a vehicle moving along a flooded roads past flooded buildings, and then a dolphin breaching and swimming]

My hope is that the need for action outweighs the reluctance to tinker. But first, of course, we need to show that we can do these things without causing harm.

[Image changes to show a diver and fish swimming around a coral reef as camera pans in and to the right]

And we need to show that we can do these things in a safe and transparent way.

[Music plays as image changes to show a white screen with the CSIRO logo, and text appears: Australia’s National Science Agency]

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Our response

Evaluating the feasibility of ocean alkalinity enhancement

CSIRO is contributing to international climate science efforts to evaluate the feasibility of OAE as a climate solution for Australia.

OAE works by speeding up the naturally occurring process in which the ocean removes CO2 from the atmosphere.

This cycle consists of the following stages:

  • Over hundreds of thousands of years, alkalinity is added to the rivers, and eventually the ocean, through the weathering of rocks on land, such as limestone or basalt.
  • Dissolved minerals make their way to the ocean as runoff. When added to the ocean, the increase in alkalinity induces a decrease in the ocean CO2 partial pressure. This ‘disequilibrium’ results in CO2 in-gassing, where the ocean uptakes additional CO2 from the atmosphere.
  • Atmospheric CO2 enters the ocean as dissolved CO2, and quickly reacts with seawater to form stable bicarbonate (HCO3-). CO2 is locked away for more than 10,000 years in the ocean and unable to easily return to the atmosphere. The air-sea equilibrium is restored.

CSIRO's CarbonLock Future Science Platform is currently exploring OAE as part of its novel CDR research portfolio. An OAE project, currently funded until June 2026, is assessing electrochemical approaches to OAE.

Electrochemical approaches to OAE involve splitting seawater into its acidic and basic components, and reintroducing the basic component back to the ocean. Any subsequent uptake of CO2 is measured through in-situ ocean sensors.

Scientists are seeking to understand the potential effects of alkalinity addition on marine phytoplankton (pictured).

Closing in on knowledge gaps around OAE

Large-scale modelling simulations have already shown OAE to be effective, but we still need to determine whether it is a potentially viable CDR technology option for Australia. Doing so requires the research community to address fundamental knowledge gaps around its feasibility, scalability, efficacy, risks and social acceptance.

The impacts (if any) of exposure to short-term increases in alkalinity are not yet fully known. The organisms most likely to be impacted are phytoplankton, the primary producers of the ocean.

Understanding the potential unintended consequences of OAE is an active area of research, including at CSIRO. It includes a variety of approaches, such as oceanography (e.g. changing ocean chemistry, sensor technology and ocean modelling); modern genomics (e.g. metabarcoding); plus conventional biomarker and isotopic methods. We are working within a multidisciplinary team to apply diverse skillsets in tackling the challenge of OAE.

The results

Improving our understanding of OAE in carefully controlled settings

Novel CDR approaches like OAE - that actively remove carbon dioxide from the atmosphere and store it away durably - are critically needed to reach the climate goals of the Paris Agreement.

Our research could help close in on important knowledge gaps around the potential deployment of OAE at scale.

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