Ocean alkalinity enhancement

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.

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.

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.