Ocean Acidification
Ocean acidification is the ongoing decrease in the pH of Earth's oceans caused by the absorption of atmospheric carbon dioxide (CO₂), which reacts with seawater to form carbonic acid. Since the Industrial Revolution, ocean surface pH has dropped from approximately 8.2 to 8.1, representing a 26% increase in hydrogen ion concentration. This process threatens marine organisms, especially those that build shells or skeletons from calcium carbonate, such as corals, mollusks, and certain plankton species.
Key Formula
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3- (carbonic acid dissociation)
LaTeX: CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-
| Symbol | Meaning | Unit |
|---|---|---|
| CO_2 | Carbon dioxide dissolved in seawater | mol/L |
| H_2CO_3 | Carbonic acid | mol/L |
| H^+ | Hydrogen ion (proton), determines acidity | mol/L |
| HCO_3^- | Bicarbonate ion | mol/L |
Worked Example
Problem
Pre-industrial ocean surface pH was 8.179. Current pH is 8.069. Calculate the percentage increase in hydrogen ion concentration [H⁺], given that pH = −log₁₀[H⁺].
Solution
Step 1: Calculate pre-industrial [H⁺]. [H⁺]_pre = 10^(−8.179) = 6.619 × 10⁻⁹ mol/L Step 2: Calculate current [H⁺]. [H⁺]_now = 10^(−8.069) = 8.531 × 10⁻⁹ mol/L Step 3: Calculate percentage increase. % increase = ((8.531 − 6.619) / 6.619) × 100 = (1.912 / 6.619) × 100 ≈ 28.9%
Answer
The hydrogen ion concentration has increased by approximately 28.9%, confirming a significant acidification of surface ocean waters.
Ocean Chemistry Changes Due to Acidification
| Parameter | Pre-Industrial (~1750) | Current (~2024) | Change |
|---|---|---|---|
| Surface pH | 8.179 | 8.069 | −0.11 units |
| pCO₂ (μatm) | 280 | 420 | +140 μatm |
| [H⁺] (nmol/L) | 6.6 | 8.5 | +28% |
| Aragonite saturation (Ω) | 3.44 | 2.90 | −15.7% |
| [CO₃²⁻] (μmol/kg) | 222 | 185 | −17% |
Interactive Tools
NOAA Ocean Acidification Program
Research data, monitoring networks, and educational resources on ocean acidification
Open ToolKhan Academy – Ocean Acidification
Explanatory videos on CO2 absorption and ocean chemistry changes
Open ToolWolfram Alpha – Chemical Equilibrium
Compute carbonate equilibrium chemistry and pH calculations
Open Tool
Wikimedia Commons, CC BY-SA
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From Latin "oceanus" (the great outer sea, from Greek "ōkeanos") and Latin "acidus" (sour) + "-fication" (the process of making). The term was formalized in scientific literature around 2003 when researchers began quantifying CO₂-driven pH changes in marine systems.