An increase in atmospheric carbon dioxide (CO2) leads to increased ocean acidity because CO2 dissolves in seawater and undergoes a series of chemical reactions that ultimately release hydrogen ions (H+), which lower the ocean's pH.
The Chemistry of Ocean Acidification
Here's a breakdown of the process:
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CO2 Absorption: The ocean absorbs a significant portion of atmospheric CO2. This absorption is governed by the partial pressure difference between CO2 in the atmosphere and CO2 dissolved in the surface ocean.
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Formation of Carbonic Acid (H2CO3): Once dissolved in seawater, CO2 reacts with water (H2O) to form carbonic acid (H2CO3):
CO2 (dissolved) + H2O ⇌ H2CO3 -
Dissociation of Carbonic Acid: Carbonic acid is unstable and quickly dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+):
H2CO3 ⇌ HCO3- + H+ -
Bicarbonate Dissociation (Less Common): Bicarbonate can further dissociate into a carbonate ion (CO32-) and another hydrogen ion (H+):
HCO3- ⇌ CO32- + H+ -
Increase in Hydrogen Ions (H+): The release of hydrogen ions (H+) is the key factor in increasing ocean acidity. The more H+ ions present, the lower the pH of the seawater, and thus, the more acidic it becomes.
Impact on pH
pH is a measure of acidity or alkalinity. It's a logarithmic scale, meaning that a small change in pH represents a significant change in acidity. For instance, a decrease of 0.1 pH units represents approximately a 30% increase in acidity. Since the industrial revolution, the ocean's pH has decreased by about 0.1 pH units, demonstrating a significant increase in ocean acidity.
Impact on Marine Life
Ocean acidification has significant consequences for marine life, particularly for organisms that build shells and skeletons from calcium carbonate (CaCO3), such as:
- Shellfish: Oysters, clams, mussels
- Corals: Reef-building corals
- Plankton: Coccolithophores, foraminifera
The increased acidity reduces the availability of carbonate ions (CO32-), which these organisms need to build and maintain their calcium carbonate structures. This makes it more difficult for them to form shells and skeletons, weakens existing structures, and can even cause shells to dissolve.
Example: Coral Reefs
Coral reefs are particularly vulnerable to ocean acidification. As the ocean becomes more acidic, coral growth slows down, and existing coral skeletons can dissolve. This weakens the entire reef ecosystem, making it more susceptible to damage from storms and other stressors. Loss of coral reefs has cascading effects on the entire marine ecosystem, impacting biodiversity and coastal protection.
Solutions
The primary solution to ocean acidification is to reduce atmospheric CO2 levels by:
- Reducing Fossil Fuel Emissions: Transitioning to renewable energy sources like solar, wind, and hydropower.
- Improving Energy Efficiency: Reducing energy consumption through better insulation, transportation, and industrial processes.
- Carbon Capture and Storage: Developing technologies to capture CO2 from power plants and industrial sources and store it underground.
- Reforestation and Afforestation: Planting trees and restoring forests to absorb CO2 from the atmosphere.
