Researchers propose small-scale ocean alkalinity for local carbon management

Researchers say ocean alkalinity enhancement (OAE) should shift from a geoengineering intervention (large-scale intervention in Earth's climate) to a practical, flexible tool for local CO2 management. The argument appears in an article in Nature Reviews Earth & Environment, reported by Phys.org on 7 October. Lead author Lennart Bach, an associate professor and biogeochemical oceanographer at the University of Tasmania's Institute for Marine and Antarctic Studies (IMAS), said integrating small-scale OAE into local contexts could deliver the carbon mitigation goals set by individual governments and communities.

Bach said a city council might find its domestic wastewater emissions could be mitigated with alkalinity from silicate minerals. He said a regional wind farm might not need to shut off during excess wind if the surplus energy instead increased seawater alkalinity electrochemically, using electricity. He said upscaling across such local areas could work only if the pathways are environmentally responsible, demonstrably carbon negative and earn public trust.

According to the article, OAE reduces acidity in seawater and converts CO2 into mainly inert bicarbonate ions, which can be stored in the ocean for millennia. Co-author Dr. Damon Britton, an IMAS researcher, said the chemistry is scientifically understood and predictable, and that available evidence suggests storing carbon as bicarbonate would not harm marine life. He said natural alkalinity is carried by rivers into the sea and has regulated the climate throughout Earth's history.

Britton said OAE also changes the environment in ways beyond raising alkalinity. Depending on the method used, he said, it can increase turbidity — the cloudiness of the water — and introduce additional elements such as trace metals. He said understanding how these changes interact with local marine life is critical to knowing where small-scale OAE can be safely implemented and whether the environmental risks outweigh the benefits.

Co-author Dr. Tyler Rohr, also an IMAS researcher, said that in theory the ocean has more than enough space to store all human emissions. He said raising the ocean's mean alkalinity by about 2% would store the roughly 2,660 billion tonnes of CO2 released since the Industrial Revolution. He said it is not obvious how that much alkalinity could be spread evenly across the global ocean and kept in contact with the atmosphere long enough to absorb its full potential of CO2, and that in practice concentrated alkalinity must be delivered from specific point sources.