Planetary Technologies plans to conduct more ocean alkalinity enhancement experiments in Halifax Harbour. Image Credit: Planetary Technologies via ScienceIn August 2023, Planetary Technologies conducted an ocean alkalinity enhancement experiment in Halifax Harbour, Nova Scotia, Canada. Researchers introduced minerals commonly found in antacid medication into the waters near a coastal power plant, turning the water milky pink. The experiment was not meant to treat acidity in the human body. Instead, it sought to increase the levels of alkalinity in the oceans in order to facilitate the absorption of carbon dioxide (CO₂) from the atmosphere into the ocean.According to Phys.org, this experiment was carried out by the Canadian climate tech firm Planetary Technologies, which released roughly 280 tons of magnesium hydroxide, an alkaline mineral that is also used in various other products including Milk of Magnesia in Halifax Harbour over two months. The approach is known as ocean alkalinity enhancement, an emerging research field.How adding an antacid-like mineral can remove carbon dioxideThe oceans play a major role in regulating Earth’s climate. According to the National Oceanic and Atmospheric Administration (NOAA), oceans absorb about a quarter of carbon dioxide emissions produced by humans and thereby reduce the presence of CO₂ in the atmosphere.When carbon dioxide enters the ocean, it combines with water molecules to form carbonic acid. This leads to ocean acidification, which can have adverse effects on marine life. Oceans can be made alkaline by introducing minerals like magnesium hydroxide and limestone into the seawater. They release hydroxide ions that combine with dissolved carbon dioxide and form bicarbonate. Studies suggest that when carbon dioxide is converted to bicarbonate in the ocean, it can remain stored for thousands of years, increasing the ocean’s carbon-storage capacity.The alkaline mineral brucite can raise the pH of ocean water and trigger carbon dioxide–capturing reactions. Image Credit: ScienceWhat took place during the Halifax experiment?During the experiment, the company added magnesium hydroxide to seawater and then released it via a discharge pipe connected to a local power plant. To trace the movement of the alkaline mixture, scientists used a harmless dye called rhodamine.Researchers from Dalhousie University studied changes in pH, alkalinity and carbon concentration to see whether the process could increase carbon dioxide absorption. According to a report published by Science, Planetary estimated that the experiment could lead to more than 200 tons of additional carbon dioxide being absorbed by the sea; however, the amount of carbon actually stored is still a matter of debate among scientists.Why do scientists study this concept?The main advantage is the ocean’s vast size. The ocean contains much more carbon than the atmosphere – mostly bicarbonate and carbonate ions. Higher alkalinity may help the ocean absorb more CO₂ while also reducing ocean acidification.Alkalinity enhancement could theoretically remove substantial amounts of carbon dioxide from the atmosphere, but scientists warn of major uncertainty about environmental impacts, costs and limitations. Climate scientists and carbon-removal companies are interested in the method because it could complement emissions reductions. However, scientists keep saying that carbon removal methods cannot compensate for fossil fuel emissions reduction.Experts caution that the ocean cannot be treated as a risk-free laboratoryAlthough the basic science is straightforward, scaling the method up will be difficult. One of the biggest challenges is proving how much extra CO2 the intervention absorbs, because ocean chemistry varies with tides, temperature, biology and currents.Researchers are also studying the effects of the added minerals on marine ecosystems. Some minerals may contain traces of certain metals and therefore affect plankton and other living organisms. Adding alkaline materials to the ocean should be carefully assessed because it can have complex effects on seawater chemistry. Scientists also point to earlier debates over ocean experiments. In 2012, an experiment near the Haida Gwaii islands of Canada added iron to the water to stimulate plankton growth and carbon absorption.The question is whether the approach can become a climate solutionCompanies pursuing ocean alkalinity enhancement believe the technology could work on a much larger scale. Still, to have a significant climate impact, huge amounts of minerals would need to be mined, transported and managed. Experts say the next few years will be decisive in determining whether the technology can move beyond the experimental stage.For now, the pink water of Halifax Harbour is a small but scientifically important test of whether humans can speed up a natural climate process without causing environmental harm. Scientists are exploring several ways to remove carbon dioxide from the atmosphere. It remains unclear whether the ocean can be used safely for this purpose.