The primary cause of oceanic acidification is the absorption of carbon dioxide (CO2) from the atmosphere by the ocean. When CO2 dissolves in seawater, it forms carbonic acid, leading to a decrease in pH levels, thus making the ocean more acidic. This process affects marine life, particularly organisms with calcium carbonate shells or skeletons, like corals and mollusks. Monitoring and mitigating acidification is crucial to maintaining marine biodiversity and ecosystem health.