1.
Ocean acidification has multiple consequences on marine life, including reducing
availability of carbonate for skeletal formation of ocean organisms, increasing coral
bleaching, and other impacts. The main driver of the increasing acidity of our oceans is:
a. Increased ozone that reacts with water to release hydrogen atoms
b. Increased plastic pollution which breaks down in the water
c. Increased CO2 that reacts with water to form carbonic acid and then bicarbonate
d. Reduction in marine life which decreases the amount of ammonia waste
Ocean acidification decreases ocean pH primarily through CO2 absorption, harming shell-forming organisms and corals. The correct answer is option c. This MCQ tests understanding of chemical mechanisms in environmental biology.
Question Breakdown
The query asks for the main driver behind ocean acidification’s consequences, such as reduced carbonate for skeletons and increased coral bleaching. Atmospheric CO2 dissolves in seawater, forming carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃⁻) and H⁺ ions, lowering pH. Since pre-industrial times, ocean pH has dropped by 0.1 units, a 30% acidity increase.
Option Analysis
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a. Increased ozone reacting with water: Ozone (O₃) depletion affects UV radiation and indirectly climate but does not directly acidify oceans via hydrogen release; it resides in the stratosphere.
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b. Increased plastic pollution: Plastic degradation releases organic acids and CO₂ under sunlight, contributing minor pH drops (up to 0.5 units locally), but it is not the primary driver.
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c. Increased CO₂ forming carbonic acid and bicarbonate: Correct. CO₂ + H₂O → H₂CO₃ → HCO₃⁻ + H⁺ reduces carbonate (CO₃²⁻) availability, impairing calcification in corals, shellfish, and plankton.
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d. Reduction in marine life decreasing ammonia: Less marine life might alter local pH via reduced ammonia oxidation, but population declines result from acidification, not cause it; ammonia-oxidizing microbes face inhibition under low pH.
Chemical Mechanism
CO₂ absorption follows:
CO₂ (aq) + H₂O ⇌ H₂CO₃
H₂CO₃ ⇌ HCO₃⁻ + H⁺
HCO₃⁻ ⇌ CO₃²⁻ + H⁺.
This shifts equilibrium, decreasing saturation states for CaCO₃, essential for marine skeletons. Fossil fuel emissions drive ~90% of this change.
Impacts on Marine Ecosystems
Acidification dissolves shells of pteropods and oysters, disrupts coral symbiosis leading to bleaching, and alters food webs. Fisheries face $1 billion annual losses by 2100. Mitigation requires cutting CO₂ emissions. For CSIR NET, link to biogeochemical cycles.
