Final answer:
Ocean acidification is caused by increased carbon dioxide from human activities dissolving in ocean waters, lowering the pH and affecting marine life.
Step-by-step explanation:
Human disruption of the carbon cycle causes ocean acidification primarily through the increased levels of carbon dioxide (CO2) in the atmosphere dissolving into ocean waters. Fossil fuel burning has elevated atmospheric CO2 concentration, and when this CO2 enters the ocean, it reacts with water to form carbonic acid, which then disassociates, lowering the pH of the ocean water and leading to acidification. As a result, the ocean's acidity impacts marine life, particularly those species like corals and shellfish that rely on calcium carbonate for their exoskeletons. Rising acidity impedes their ability to calcify, threatening the diversity and stability of marine ecosystems.