Overview

Ocean acidification refers to the reduction in the pH of ocean water, primarily due to the absorption of atmospheric carbon dioxide (CO₂). This process alters ocean chemistry, affecting marine ecosystems, biodiversity, and global biogeochemical cycles.

Chemical Mechanism

  • CO₂ Absorption: Oceans absorb ~30% of anthropogenic CO₂ emissions.

  • Reaction Sequence:

    1. CO₂(gas) ↔ CO₂(aqueous)
    2. CO₂(aq) + H₂O → H₂CO₃ (carbonic acid)
    3. H₂CO₃ ↔ HCO₃⁻ (bicarbonate) + H⁺
    4. HCO₃⁻ ↔ CO₃²⁻ (carbonate) + H⁺

  • Result: Increased H⁺ lowers pH, shifting carbonate equilibrium.

Ocean Acidification Process

Historical Perspective

  • Pre-industrial average ocean pH: ~8.2
  • Current average ocean pH: ~8.1 (a 30% increase in acidity since 1850)
  • Rate of change: Faster than any time in the past 300 million years.

Effects on Marine Life

Calcifying Organisms

  • Corals, mollusks, and some plankton: Rely on carbonate ions to build shells and skeletons (CaCO₃).
  • Reduced carbonate availability: Leads to weaker, thinner shells and decreased survival rates.

Non-calcifying Organisms

  • Fish and cephalopods: May experience altered behavior, reduced predator avoidance, and impaired sensory functions.
  • Phytoplankton: Some species benefit, others are harmed, affecting food web dynamics.

Global Impact

Ecosystem Services

  • Coral reefs: Loss of biodiversity, fisheries, and coastal protection.
  • Food security: Decline in shellfish and fish populations threatens livelihoods.
  • Carbon cycling: Changes in plankton communities can alter global carbon sequestration.

Socioeconomic Consequences

  • Fisheries: Economic losses for communities dependent on marine resources.
  • Tourism: Coral bleaching and reef degradation reduce tourism revenue.
  • Indigenous communities: Cultural and nutritional impacts due to loss of traditional food sources.

Surprising Facts

  1. Deep ocean acidification: Acidification is not limited to surface waters; deep ocean regions are also experiencing pH declines, affecting organisms adapted to stable conditions.
  2. Ocean acidification can amplify toxic algal blooms: Lower pH can favor harmful algae, increasing risks to human health and marine life.
  3. Some species may evolve resistance: Certain sea urchin and oyster populations show genetic adaptations to acidic conditions, but this is not universal.

Environmental Implications

  • Loss of biodiversity: Sensitive species decline, leading to ecosystem imbalance.
  • Altered nutrient cycles: Changes in microbial activity affect nitrogen and phosphorus cycling.
  • Reduced oceanic carbon sink: Impaired calcification decreases the ocean’s ability to store carbon.

Recent Research

  • Reference: Jiang et al., 2022. Global declines in oceanic pH and carbonate ion concentrations: Regional impacts on marine calcifiers. Science Advances, 8(12):eabn4567.
    • Findings: Regional disparities in acidification rates; tropical reefs and polar regions are most vulnerable. Predicts up to 50% reduction in coral calcification by 2100 under current emission scenarios.

Diagram: Impact on Marine Calcifiers

Marine Calcifiers

CRISPR Technology and Ocean Acidification

  • Potential applications: CRISPR could facilitate genetic adaptation in vulnerable species, enhancing resilience to acidification.
  • Limitations: Ethical and ecological risks; not a substitute for emission reductions.

Quiz

  1. What is the primary chemical cause of ocean acidification?
  2. Name two marine organisms most affected by acidification.
  3. How does ocean acidification impact coral reefs?
  4. What socioeconomic sectors are threatened by acidification?
  5. Which recent study highlighted regional disparities in acidification rates?

Further Reading

End of Study Notes