What impact does increased carbon dioxide have on oceans?

Increased carbon dioxide (CO2) levels in the atmosphere have a significant impact on the oceans, primarily leading to ocean acidification. When CO2 is absorbed by seawater, it reacts with water to form carbonic acid, which subsequently dissociates into bicarbonate and hydrogen ions. The increase in hydrogen ions lowers the pH of the ocean, making the water more acidic.

This process has important ecological consequences. For example, many marine organisms, particularly those that rely on calcium carbonate for their shells and skeletons, such as corals, mollusks, and some plankton species, are adversely affected by lower pH levels. Ocean acidification can hinder their ability to maintain their structures, which can disrupt entire marine ecosystems and food webs.

The other options do not accurately reflect the primary impact of increased CO2 on the oceans. While photosynthesis rates may be influenced by CO2 levels, the effect on ocean acidification is much more pronounced. Ocean temperatures are influenced by various factors beyond just CO2 levels, and increased carbon dioxide does not directly lead to an increase in plankton populations, which can be more complex and dependent on additional environmental conditions.