Quantifying the ocean’s efficiency for enhanced carbon storage

Project duration: July 2023–December 2024

Project lead

Team

Benoît Pasquie

Opportunity

The ocean offers huge storage capacity for storing CO₂, with most (80%) anthropogenic CO₂ emissions eventually being stored in the ocean. However, this cycle takes thousands of years and in the process our climate will change.

One potential approach to marine carbon dioxide removal (mCDR) is directly injecting carbon dioxide (CO₂) into the deep ocean or ocean sediments. Deep ocean CO₂ injection provides a means to accelerate the ocean uptake of CO₂ or enhance the natural carbon cycle.

We’re examining deep ocean CO₂ injection alongside other mCDR approaches like ocean alkalinity enhancement (OAE).

Deep ocean CO₂ injection below the seabed is not a straightforward solution. To be considered permanent, the injected CO₂ must not rapidly return to the atmosphere.

Currently, there are knowledge gaps around the carbon sequestration efficiency of deep ocean CO₂ injection. Closing in on these gaps requires research to quantify the time it takes for carbon at the seafloor to reemerge to the surface and partially ‘outgas’ back into the atmosphere. This involves modelling a range of variables, including ocean circulation and how it may change with climate change, and geological conditions of the seabed.

Goal

The main objective of this project is to quantify the time it takes CO₂ at the seafloor to return to the surface ocean (return time). 

When stored at high pressure and low temperatures common in deep rock layers beneath the ocean, CO₂ stays in its liquid phase and is denser than sea water. While this CO₂ is chemically stable, it is also buoyant, so its permanent storage may not be guaranteed. Injected CO₂ could escape into the surrounding ocean and eventually the atmosphere.

In this project, we will:

• use climate models to simulate ocean circulation in present day as well as future (to model projected climate changes).
• estimate the return time and how it is affected by climate variability and climate change.
• produce maps of return times for whole of the Australian exclusive economic zone – the area of the ocean adjacent to Australia’s Territorial Seas (pictured below).

• produce assessments of the potential likelihood of a rapid return of the CO₂ at the sea floor to the surface ocean. 

Overall, our research will provide a novel way to assess the risk of injected CO₂ returning to the atmosphere. 

Barriers

mCDR approaches will be necessary to reach our climate goals. This is because there are only a finite number of locations CO₂ can be sequestered on land due to competing land-use needs, earthquake risk and groundwater pollution.

Australia is well-positioned to explore this opportunity given our exclusive economic zone is one of the largest in the world and provides a unique resource. Further, injecting CO₂ into deep-lying rock layers below the ocean at depths of 1000-4000 metres would further increase the ocean’s carbon storage capacity.

Research is essential to evaluate the potential of deploying this mCDR approach to reduce atmospheric carbon dioxide concentrations and future climate change. 

This fundamental research utilises our climate and ocean expertise to assess the efficacy of deep CO₂ ocean injection into the seabed as a potential novel mCDR approach. 

Importantly, the research does not advocate this mCDR approach but provides the necessary knowledge to realistically assess its benefits and risks. 

This project will help provide evidence to remove a barrier to its potential deployment.

References

Wong, C. S., & Matear, R. (1993). The storage of anthropogenic carbon dioxide in the ocean. Energy conversion and management, 34(9-11), 873-880.