Primary Cause of Ocean Acidification
Ocean acidification is primarily caused by the ocean's absorption of excess carbon dioxide (CO2) from the atmosphere. As human activities, such as burning fossil fuels, release more CO2, the gas dissolves in seawater, forming carbonic acid (H2CO3). This process lowers the ocean's pH, making it more acidic. Since the Industrial Revolution, ocean pH has decreased by about 0.1 units, representing a 30% increase in acidity.
Chemical Mechanisms Involved
The key chemical reaction begins when CO2 reacts with water to produce carbonic acid, which dissociates into bicarbonate (HCO3-) and hydrogen ions (H+). The increase in H+ ions reduces the ocean's alkalinity and pH. Other factors, like reduced buffering capacity from declining carbonate ions (CO3^2-), exacerbate the effect, as these ions are crucial for marine organisms to build shells and skeletons.
Practical Example: Impact on Coral Reefs
In coral reef systems like the Great Barrier Reef, elevated CO2 levels lead to acidification that hinders coral calcification. Corals rely on calcium carbonate (CaCO3) to form their skeletons, but lower pH dissolves this material more readily. For instance, during periods of high atmospheric CO2, such as from seasonal upwelling of deep, CO2-rich waters, reef growth slows, demonstrating how acidification directly impairs ecosystem structure.
Broader Implications and Importance
Ocean acidification disrupts marine food webs by affecting shell-forming organisms like oysters and pteropods, which are vital prey for fish and seabirds. It also influences the global carbon cycle by altering how oceans store CO2. Addressing this requires reducing emissions to mitigate risks to fisheries, biodiversity, and coastal economies dependent on healthy oceans.