Changing tides: how does ocean acidification affect marine life?

Despite how the ocean has influenced the natural world throughout history, human-triggered global warming is now changing ocean chemistry through a process called ocean acidification. Described by some researchers as “the other CO2 problem”, this phenomenon refers to the reduction in the pH of seawater over time – a change that comes with negative impacts on life above and below the waves. How does ocean acidification affect marine life and humans and what can we do to mitigate its impact?

With its powerful tides and vast expanses that stretch into the horizon, the ocean captivates us. It is the cradle of early life – over billions of years our oceans have witnessed the evolution of simple cellular organisms to the wonderfully complex communities we see today. Whether we are standing with our feet in the surf or landlocked thousands of miles from the coast, we are surrounded by the ocean’s influence. By distributing heat, sequestering carbon, and storing solar radiation, it drives weather and climate across the globe. 

What is Ocean Acidification?

Ocean acidification refers to a decrease in the pH of seawater due to increased levels of carbon dioxide (CO2) in the atmosphere. Our oceans are carbon sinks – think of them as sponges that soak up excess carbon from the atmosphere.

By natural processes, CO2 absorbed by the ocean reacts with seawater to create carbonic acid, a weak acid that breaks apart into ions of different charges (imagine ions as Lego pieces that make up a larger structure– in this case,  carbonic acid). These include hydrogen ions and bicarbonate ions. The latter disassociates further to produce additional ions of hydrogen and carbonate. Animals like corals, shellfish, oysters, and urchins  –collectively referred to as calcifiers – use carbonate to build their shells and skeletons.

How does this process change when more CO2 is added to the mix? Since the industrial revolution, the amount of CO2 in the atmosphere has risen nearly 50%, jumping up to nearly 420 parts per million. Our seas currently soak up more than a quarter of the CO2 emitted from human activity. More CO2 in the ocean means more carbonic acid is produced, resulting in extra hydrogen and bicarbonate ions in seawater. pH is determined by the number of free hydrogen ions in a solution; the more they are, the lower the pH (and the more acidic the water). Additional CO2 in the water also leads to a decrease in the bioavailability of carbonate, making it harder for calcifiers to build their shells. 

Logan Range, Earth Org, 30 August 2022. Full article.

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