Adding natural alkaline substances to seawater can boost the ocean’s ability to absorb carbon dioxide – but scientists warn there may be processes in the ocean system that alter its efficiency.
Ocean alkalinity enhancement (OAE) aims to accelerate the relatively slow weathering processes that occur naturally on land and in the coastal ocean, by grinding up alkaline minerals such as silicate and carbonate rocks and dispersing them across the ocean surface.
In a new study published in Nature Geoscience, scientists from the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS) took a closer look at how OAE could change ocean chemistry and how this could affect marine organisms in their surrounding environment.
“By shifting the carbonate chemistry of seawater, OAE has the potential to remove gigatonnes of carbon dioxide from the atmosphere and store it as carbonate and bicarbonate in the ocean,” IMAS researcher and lead author of the study, Dr Nadine Lehmann said.
“But it is critical to assess potential feedbacks between enhanced alkalinity and the marine ecosystem, so we can ensure OAE is environmentally safe and sustainable before it is deployed at scale.”
IMAS researcher and study co-author, Associate Professor Lennart Bach said extreme alkalinity enhancement could cause the proliferation of coccolithophores, which are single-celled calcifying phytoplankton that cover themselves with a calcium carbonate shell.
“We found that shifting the seawater carbonate equilibrium could benefit calcifying organisms like coccolithophores, with the increased calcification strongly reducing the efficiency of alkalinity enhancement.”
The study revealed that extreme alkalinity enhancement provides a competitive advantage for coccolithophores so they contribute more biomass to plankton blooms – and could reduce the carbon dioxide removal potential of ocean alkalinity enhancement by 2–29% by 2100.
“However, we found that lower levels of alkalinity enhancement may reduce the severity of ocean acidification on coccolithophores, which naturally play an important role in the marine carbon cycle,” Dr Lehmann said.
“Our findings show that it is critical to consider large-scale feedbacks in the ocean system when evaluating the efficiency of ocean alkalinity enhancement.
“But importantly, by investigating these ocean systems we can quantify these feedbacks. And this will confirm whether carbon dioxide removal like OAE may contribute to Australia and the world’s goal to halt global warming.”
Discover more about our ocean alkalinity enhancement research at IMAS
Cover image
Credit: Nico Marin
Ocean Image Bank