Ocean Acidification

For over 200 years since the Industrial Revolution, atmospheric carbon dioxide (CO2) levels have increased due to the burning of fossil fuels and land use changes. The ocean absorbs about 30% of this CO2, leading to higher CO2 levels in seawater. This absorption triggers chemical reactions that increase hydrogen ion concentration, making the water more acidic and reducing carbonate ion availability.

Doney (Doney, S. C., et al. 2009) noted that "Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater's chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is lowering calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals."

Carbonate ions are crucial for building shells and skeletons in marine organisms like oysters, clams, sea urchins, corals, and plankton. Reduced carbonate ion levels hinder these organisms' ability to maintain their structures. Additionally, more acidic waters can impair the behaviour of non-calcifying organisms, such as certain fish, making them less able to detect predators, threatening the entire food web.

Ocean acidification impacts global oceans, including coastal areas, affecting economies reliant on fishing and shellfish. Many people worldwide depend on ocean-sourced food as their primary protein source.

Richardson (Richardson, K. 2023) noted that "anthropogenic ocean acidification currently lies at the margin of the safe operating space, and the trend is worsening as anthropogenic CO2 emission continues to rise."