Overview

Ocean acidification refers to the ongoing decrease in ocean pH caused by the absorption of atmospheric carbon dioxide (CO₂). This chemical process impacts marine ecosystems, biodiversity, and global cycles.

Chemical Process

  • CO₂ Absorption: Oceans absorb ~30% of anthropogenic CO₂ emissions.
  • Formation of Carbonic Acid:
    CO₂ (gas) + H₂O (liquid) → H₂CO₃ (carbonic acid)
  • Dissociation:
    H₂CO₃ → HCO₃⁻ (bicarbonate) + H⁺ (hydrogen ion)
    HCO₃⁻ → CO₃²⁻ (carbonate) + H⁺
  • Lower pH: Increased H⁺ ions result in lower pH (more acidic water).

Ocean Acidification Process

Historical Context

  • Pre-Industrial Era: Ocean pH averaged ~8.2.
  • Current pH: Since the Industrial Revolution, average surface ocean pH has dropped to ~8.1.
  • Geological Scale:
    • Water cycles through evaporation, precipitation, and runoff, meaning the water we drink today may have been consumed by dinosaurs millions of years ago.
    • Past mass extinctions (e.g., Permian-Triassic) have been linked to rapid ocean chemistry changes.

Impact on Marine Life

  • Calcifying Organisms:
    • Shellfish, corals, and some plankton struggle to form calcium carbonate shells/skeletons.
    • Reduced carbonate ion availability impairs shell formation.
  • Food Webs:
    • Disrupted base of marine food chains (e.g., pteropods).
  • Behavioral Changes:
    • Fish and invertebrates show altered sensory and predator avoidance behaviors.

Case Study: Great Barrier Reef

  • Location: Northeastern Australia
  • Problem:
    • Coral calcification rates have declined.
    • Increased bleaching events due to combined stressors (acidification + warming).
  • Recent Observations:
    • 2022: Australian Institute of Marine Science reported lowest coral cover in decades.
    • Acidification impairs coral larvae settlement and growth.
  • Socioeconomic Impact:
    • Threatens tourism, fisheries, and indigenous livelihoods.

Surprising Facts

  1. Dinosaur Water:
    The molecules in the water you drink today may have passed through the bodies of dinosaurs, highlighting the ancient and recycled nature of Earth’s water cycle.
  2. Invisible Threat:
    Ocean acidification is often called the “evil twin” of climate change because it is less visible but equally dangerous to marine ecosystems.
  3. Rapid Change:
    Current ocean acidification rates are estimated to be 10 times faster than any event in the last 55 million years, outpacing the adaptive capacity of many species.

Ethical Issues

  • Intergenerational Justice:
    • Future generations will inherit degraded oceans and reduced marine biodiversity.
  • Global Responsibility:
    • Industrialized nations contribute most CO₂ emissions, but vulnerable coastal communities and developing countries face the greatest risks.
  • Biodiversity Loss:
    • Ethical dilemma in balancing economic growth and the preservation of irreplaceable marine life.
  • Access to Resources:
    • Ocean acidification threatens food security for millions who depend on seafood.

Recent Research

  • Citation:
    Kroeker, K.J., et al. (2020). “Impacts of ocean acidification on marine organisms: Quantifying sensitivities and interactions with warming.” Global Change Biology, 26(1), 321-329.
  • Key Findings:
    • Combined effects of acidification and warming amplify stress on marine species.
    • Some species show resilience, but ecosystem-level impacts are severe.
    • Calls for integrated mitigation strategies.

Mitigation & Adaptation

  • Reducing CO₂ Emissions:
    • Transition to renewable energy.
    • Carbon capture technologies.
  • Marine Protected Areas:
    • Safeguarding vulnerable ecosystems.
  • Restoration Projects:
    • Coral gardening, oyster reef restoration.
  • Policy Actions:
    • International agreements (e.g., Paris Agreement).

Diagram: Effects on Shell Formation

Shell Dissolution

Summary Table

Factor Pre-Industrial Current (2024) Projected (2100)
Surface Ocean pH ~8.2 ~8.1 ~7.7–7.8
CO₂ (ppm) ~280 ~420 >700
Coral Reef Health Stable Declining Severe Loss

References

  • Kroeker, K.J., et al. (2020). “Impacts of ocean acidification on marine organisms: Quantifying sensitivities and interactions with warming.” Global Change Biology, 26(1), 321-329.
  • Australian Institute of Marine Science (2022). “Long-term monitoring of the Great Barrier Reef.”