Which gas alters the ocean's pH?

Carbon dioxide (`CO_2` ) is the primary gas responsible for the acidification of the ocean. Carbon dioxide is absorbed into the ocean from the atmosphere.

Sources of Carbon Dioxide

There are both natural and man-made sources of carbon dioxide in the atmosphere.

• 
  Natural Sources: decomposition of organic substances, volcanic eruptions, normal exchange between the atmosphere and the ocean, respiration

• Man-made Sources: fossil fuels, deforestation

The acidity of the ocean has increased 30% since the onset of the industrial revolution.

Acidification of the Ocean

Carbon dioxide reacts with water in the ocean to produce carbonic acid. This increases the concentration of hydrogen ions in the ocean and lowers the pH. The lower the pH of the ocean, the more acidic it is. Hydrogen ions also tend to bind up carbonate ions. Carbonate is needed by shell-building organisms to produce shells.