Ocean Acidification

Ocean acidification refers to the ongoing decrease in the pH of ocean water caused by the uptake of carbon dioxide (CO2) from the atmosphere. When CO2 dissolves in ocean water, it forms carbonic acid (H2CO3) and increases the concentration of hydrogen ions (H+), making the water more acidic.

Pre-Industrial vs Current pH Levels

• Pre-industrial revolution pH of ocean water: Approximately 8.179
• Current pH of ocean water: Approximately 8.069 (as of 2022)

This corresponds to a 28.8% increase in H+ ion concentration since the 18th century and industrialization.

Causes

The main cause of ocean acidification is the rise in atmospheric CO2 levels from human activities like burning fossil fuels and deforestation. The ocean absorbs about 30% of the CO2 emitted into the atmosphere, increasing the acidity of the water.

Impacts on Ocean Life

Ocean acidification can negatively impact calcifying organisms like corals, crustaceans, molluscs, and some forms of plankton that rely on calcification for shell-building and other processes. Impacts include:

• Decreased calcification rates – the decreasing pH makes it more difficult for organisms to form shells and skeletons out of calcium carbonate (CaCO3). The water becomes undersaturated with carbonate ions which are needed for calcification.
• Increased shell dissolution – the more acidic water starts to dissolve the shells of animals like clams, oysters, coral reefs, etc.
• Hypercapnia – excess CO2 absorbed can cause acidification of body fluids in animals, potentially impairing respiration, circulation, and other systems

This can disrupt ocean food chains and ecosystems, negatively impacting species like fish and marine mammals that rely on shelled animals for food and habitat. Entire reef systems may be threatened by ocean acidification over time.

Mitigation Strategies

Strategies to mitigate ocean acidification include:

• Reducing global CO2 and other greenhouse gas emissions, which can slow or limit the further acidification of ocean waters
• Protecting and restoring wetlands, seagrass beds, mangroves and coral reefs which help absorb CO2 from the local marine environment
• Supporting more resilient forms of aquaculture and fisheries management to adapt to changes in ocean chemistry
• Geoengineering solutions like artificial ocean alkalinization, though the feasibility and scale of these solutions remains uncertain.