How does increased carbon dioxide concentration affect oceans?

Increased carbon dioxide concentration in the atmosphere leads to a phenomenon known as ocean acidification. When carbon dioxide is absorbed by seawater, it reacts with water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. This process lowers the pH of the ocean, making it more acidic.

Ocean acidification has significant impacts on marine life, particularly organisms that rely on calcium carbonate to form shells and skeletons, such as coral reefs, mollusks, and certain plankton species. These organisms face challenges in maintaining their structural integrity and may experience reduced growth rates, which can disrupt the broader marine ecosystem.

The other options present scenarios that, while related to the effects of CO2, do not accurately reflect the primary consequence of increased carbon dioxide concentrations in the oceans. For example, while increased nutrient availability might promote algae growth, this process is more complex and not solely linked to carbon dioxide levels. Water temperature can be influenced by various factors, and fish populations may fluctuate due to multiple ecological factors, but not solely as a direct consequence of increased CO2. Thus, the most direct and significant effect of rising carbon dioxide concentrations on oceans is indeed ocean acidification.