Enhancing the ocean’s ability to remove CO2 particles from the atmosphere will be crucial in the fight against climate change, according to a new research paper led by Heriot-Watt University.

At present, around 25% of all CO2 emitted to the air is absorbed by the oceans. When these molecules enter the water they cause acidification, having a negative impact on marine environments, particularly for shell forming organisms such as crabs and shellfish that rely on fragile eco-systems for survival.

But in a joint research paper published in the academic journal, Joule, academics from Heriot-Watt University in Edinburgh and the University of Hamburg, believe they have found a way to increase the amount of CO2 stored in the ocean without causing additional acidification.

They have developed an engineering process to manufacture at scale a naturally occurring, although rare, hydrated carbonate mineral known as ikaite. Rich in calcium, this mineral, when exposed to sea water, dissolves and converts CO2 into a bicarbonate (HCO3) ions, which is a chemical compound that neutralises acidity. The scientists say this could lead to significantly more CO2 being retained by the oceans for hundreds of thousands of years.

Dr Phil Renforth from the Research Centre for Carbon Solutions (RCCS) at Heriot-Watt University, proposed the idea and is leading a project to explore the feasibility of this approach. He explains: “In order to avoid dangerous climate change and to meet the UN’s targets of reaching net zero by 2050, then it has become apparent that we must remove CO2 for our atmosphere. This is an enormous challenge but our idea is to utilise the world’s oceans.”

The academic team of geochemists and engineers have proposed a production method for ikaite that can be replicated at scale as two key materials required – limestone and water – are in plentiful supply. It works by placing limestone and water into a reactor alongside pressurised CO2. The limestone dissolves and the resulting ‘hard water’ is placed inside another reactor where it is exposed to low pressures. This pressure-swing creates crystals of ikaite which can be removed from the reactor and added to the ocean, increasing its alkalinity and removing carbon dioxide from the atmosphere.

In order to maintain its chemical stability, the ikaite needs to be deposited in waters no warmer than 15 degrees Celsius such as in northern Europe, Russia, parts of Australia, South America and South Africa.

The full research paper, titled, Using ikaite and other hydrated carbonate minerals to increase ocean alkalinity for carbon dioxide removal and environmental remediation, can be viewed in the academic journal, Joule.