Ocean Acidification Science

Climate change, often referred to as global warming, is all over the news. Everyone has heard of it. But climate change has a lesser-known partner – ocean acidification. The current pH of the ocean is 8.1-8.2, making it alkaline compared to distilled water, which has a neutral pH of 7. Ocean acidification is defined as the lowering of pH in ocean waters, resulting in increased acidity. 

Now how is this related to climate change? Both phenomena are closely linked to the carbon cycle, and the human influence on that cycle. In the ocean, the carbon system is the major control on pH and is linked to biological processes.

There are several species involved in the oceanic carbon play – carbon dioxide (CO2), carbonic acid (H2CO3), bicarbonate (HCO3-), carbonate (CO32-), and hydrogen and hydroxide ions (H+ and OH-). For organisms like shellfish and hard corals, the goal is for carbonate to be present so that it can react with calcium to form calcium carbonate, also known as calcite (CaCO3), so that they may form their shells and structural backbones.

However, things become tricky for these sea creatures when there is an increase in input of carbon dioxide to the system. When carbon dioxide reacts with water the solution becomes acidified as a result of production of H+ ions. These H+ ions lower pH. The subsequent decreased pH shifts the equilibrium of the carbonate system. Carbon dioxide is favored in acidic conditions, bicarbonate is favored in neutral conditions, and carbonate is favored in alkaline conditions. Thus, lowering the pH drives the chemical equilibrium of the ocean away from storing up carbonate and toward dissolving it. 

This is bad news for shellfish, corals, certain species of phytoplankton, and any other ocean friends who utilize calcium carbonate as part of their structure. At best a lack of calcium carbonate will reduce growth in these organisms – at worst it can actively dissolve them.

The narrative on climate change at the moment is that it is as simple as “global warming” – however, the impact on the ocean as a function of close ties to the carbon cycle proves otherwise.