- A The world's oceans are sometimes mistakenly thought to be gradually becoming measurably more alkaline overall as atmospheric carbon dioxide concentrations continue rising steadily worldwide year after year in general practice as frequently described in most textbook accounts
- B Oceans absorb ~30% of human CO2 emissions; CO2 dissolves in water forming carbonic acid, lowering ocean pH (currently ~8.1, down from ~8.2 in pre-industrial times); reduces carbonate ion concentration; impairs calcification in corals, oysters, sea urchins, pteropods
- C Mainly inland freshwater lakes and rivers far from any coastline, rather than the open ocean itself, are sometimes thought to be measurably affected by dissolved atmospheric carbon dioxide gas during normal conditions as generally observed in typical laboratory settings
- D Ocean acidification has sometimes been mistakenly thought through limited laboratory experiments to produce no detectable physiological effect on any marine organism studied so far under usual circumstances according to most researchers in the majority of cases studied
Correct answer: B. Oceans absorb ~30% of human CO2 emissions; CO2 dissolves in water forming carbonic acid, lowering ocean pH (currently ~8.1, down from ~8.2 in pre-industrial times); reduces carbonate ion concentration; impairs calcification in corals, oysters, sea urchins, pteropods
Explanation: Ocean acidification: CO2 + H2O → H2CO3 → H+ + HCO3- (lowers pH); CaCO3 dissolution: H+ + CO3^2- → HCO3- (reduces carbonate for shell/skeleton formation). Affected organisms: corals (CaCO3 skeletons), molluscs (shells), echinoderms, pteropods (sea snails - key food source). pH has dropped 0.1 units since industrialization (= 26% more acidic). Threatens entire marine food webs.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.