Scientists pumped approximately 16,200 gallons of sodium hydroxide into the Gulf of Maine. It was the final phase of a study on a climate intervention that could simultaneously mitigate global warming and ocean acidification.
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Earth’s oceans absorb about one-third of human carbon emissions. However, as this carbon dioxide dissolves into the ocean, it reacts with seawater to form carbonic acid, disrupting the ocean’s chemical balance and reducing its capacity to absorb more carbon. The average pH of surface seawater has increased in acidity by 30% since the Industrial Revolution. Sodium hydroxide, also known as lye, is caustic at high concentrations, but is commonly used in municipal water treatment as a pH/alkalinity adjuster.
The acidification of seawater alters the physiology of ocean organisms, disrupting their metabolisms, sensory perception, reproduction and communication. Acidification is especially harmful to calcifiers, including corals, mollusks and crustaceans. These animals construct their shells from the alkaline minerals in the seawater, which become less available as the pH of the water decreases due to acidification—coral reefs alone support 25% of marine species.
Ocean alkalinity enhancement
Scientists have proposed something called ocean alkalinity enhancement (OAE) to solve the problem. They plan to modify the oceans’ chemistry, making the water more alkaline, which will allow the seas to absorb more carbon dioxide. Scientists caution that this will be entirely ineffective without reducing emissions, though.
The Woods Hole Oceanographic Institution (WHOI) received approval from the EPA in April to conduct a small-scale environmental research trial of OAE in the Gulf of Maine as part of the LOC-NESS Project.
In August, a team of scientists from WHOI dispersed sodium hydroxide into federally controlled waters approximately 50 miles off the coast of Massachusetts. They dyed the substance red to make it easier to track. The main research vessel and a team of four autonomous underwater robots took regular seawater samples.
The pH of the water initially rose to approximately 8.3 from typical conditions of 7.9. The pH returned to baseline values by the end of the four-day monitoring period.
Experts estimate that ocean alkalinity enhancement could remove between one and 15 billion tons of carbon dioxide from the atmosphere. However, the investment required to accomplish this could be equivalent to that of the global cement industry. In other words, expensive.
The researchers from WHOI will spend the next few months analyzing the samples collected. “We conducted this research hoping that it would help evaluate the effectiveness and environmental impact of OAE, and though we have a lot of analysis to do, we are confident that we’ll have rigorous results that advance scientific knowledge of OAE’s environmental impact,” said Adam Subhas, associate scientist in marine chemistry and geochemistry at WHOI, and project lead of LOC-NESS.
