Looking to the Mighty Mississippi for climate solutions
Researchers measure alkalinity flowing into the Gulf of Mexico to assess a potential carbon dioxide removal strategy
The ocean has absorbed nearly a third of the carbon dioxide pumped in the atmosphere over the last century, making it among our top allies in the fight against climate change. Yet, our planet is still on track to exceed a global 1.5° C (2.7° F) temperature increase within the next 20 years. If cutting our reliance on fossil fuels won’t be enough to stave off a climate catastrophe, can the ocean do even more to help?
WHOI chemist Adam Subhas seems to think so. He and his colleagues are studying a potential Carbon Dioxide Removal (CDR) technique known as ocean alkalinity enhancement that would involve modifying the ocean’s chemistry to allow it to pull more carbon dioxide from the atmosphere into the ocean.
Specifically, the idea is to discharge dissolved alkalinity into sea water from the coast, or disperse it directly into the ocean via ships. This would cause two things to happen. First, as alkaline molecules react with carbon dioxide in the water, the concentration of carbon dioxide gas would go down. This, in turn, would disrupt the equilibrium between air and water, drawing more carbon dioxide from the air into the water.
This natural reaction has been happening for billions of years as alkalinity from weathered rock and shells mix into the ocean—but it happens very slowly on geological timescales. Ocean alkalinity enhancement has the potential to speed up the process significantly and remove gigatons of carbon dioxide from the atmosphere each year, according to the researchers.
The strategy has another potential benefit. As higher levels of carbon dioxide have been absorbed into the ocean, they have caused the pH of seawater to drop and ocean acidity to rise. This phenomenon, known as ocean acidification, is making it increasingly difficult for marine organisms like corals, clams, snails, and other organisms to continue to build their shells and skeletons. The changes in water chemistry are also reducing the amount of carbonate ions in the ocean—the primary building blocks of shell building. Adding alkalinity to the ocean may help counteract ocean acidification.
But before anyone can start adding alkalinity to the ocean, Subhas and his team first need to determine what effects a large-scale alkalinity enhancement project might have on biological and chemical systems in the ocean.
As part of this research, Subhas and his team are looking at natural alkalinity flowing out of the Mississippi River—which has an extremely high alkalinity concentration—to determine how efficient the river is at delivering carbon and alkalinity into the Gulf of Mexico. They are doing this by conducting surveys of the river in the fall, when alkalinity and carbon concentrations are very high, and in the spring, when concentrations plummet.
“By contrasting this fall survey with the one we did in the spring of 2022, we are hoping to determine how the loading of alkalinity affects the durability of carbon storage,” said Subhas.
The team has already analyzed the samples collected during the spring survey and have seen small-but-measurable amounts of alkalinity being lost from the river water as it mixes into the Gulf. This means that the alkalinity delivery process is less than 100% efficient.
“By studying this delivery efficiency over time,” said Subhas, “we can begin to understand how effective large-scale ocean alkalinity enhancement might be at sequestering carbon and thereby quantify how effective an engineered ocean alkalinity enhancement effort might be as a viable solution for carbon dioxide removal.”