How Does Ocean Acidification Affect the pH Level?

Ocean acidification directly causes a decrease in the pH level of seawater.

The Process: CO2 Absorption and pH Change

The Earth's oceans play a crucial role in absorbing carbon dioxide (CO2) from the atmosphere. However, as atmospheric CO2 levels rise due to human activities, the ocean absorbs an increasing amount of this gas.

According to the provided reference, as the ocean continues to absorb more CO2, the pH decreases and the ocean becomes more acidic. This statement highlights the fundamental impact of ocean acidification on seawater chemistry. The term "more acidic" in this context means the pH is moving towards the acidic end of the scale (below 7), even though the ocean currently remains basic (pH > 7).

Why pH Decreases

When CO2 is absorbed by seawater, it reacts with water (H₂O) to form carbonic acid (H₂CO₃). This carbonic acid quickly dissociates, releasing hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻).

The increase in hydrogen ions (H⁺) in the water is what lowers the pH level. Remember, pH is a measure of the concentration of hydrogen ions; a higher concentration of H⁺ ions means a lower pH and therefore, more acidic conditions.

• CO₂ (from atmosphere) + H₂O (water) → H₂CO₃ (carbonic acid)
• H₂CO₃ → H⁺ (hydrogen ion) + HCO₃⁻ (bicarbonate ion)

The release of these extra hydrogen ions drives the decrease in ocean pH.

Current State and Trend

The ocean's average pH is currently around 8.1. This value is basic (or alkaline), not acidic. However, the significant point is the direction of change. The reference notes that while the ocean is basic, it is becoming more acidic relative to its past pH levels as it absorbs more CO2. This downward trend in pH is the defining characteristic of ocean acidification.

Visualizing the Effect

Here's a simple look at the cause and effect:

In summary, ocean acidification is the process driven by increased atmospheric CO2 absorption that directly results in a lower pH level of seawater.