I. Rain forests produce more oxygen than that produced by oceans.
II. Marine phytoplankton and photosynthetic bacteria produce about 50% of world’s oxygen.
III. Well-oxygenated contains surface water several folds higher oxygen than that in atmospheric air.
Which of the statements given above is/are correct?
Explanation
Oxygen production is critical for Earth’s atmosphere, primarily driven by photosynthesis in marine and terrestrial ecosystems.
Statement I is incorrect: Oceans, not rainforests (Amazon, Congo), are the primary oxygen producers. NOAA estimates 50-80% of global oxygen from marine phytoplankton in the photic zone (top 200 meters). NASA cites 50-85%, with Prochlorococcus (a cyanobacterium) contributing 5-20%. Rainforests produce ~28% (National Geographic, WWF), with other terrestrial plants adding ~2%. Oceans’ dominance stems from 71% Earth’s surface and phytoplankton’s rapid turnover (days vs. decades for trees).
Statement II is correct: Marine phytoplankton (diatoms, dinoflagellates) and photosynthetic bacteria (cyanobacteria, e.g., Prochlorococcus) are the main oceanic oxygen producers. NOAA and Smithsonian confirm 50-80% of global oxygen from oceanic photosynthesis, with NASA and WWF estimating 50-85%, including 5-20% from Prochlorococcus. Photosynthesis in the photic zone uses sunlight, CO₂, and nutrients, supporting the marine food web and atmospheric oxygen. The ~50% estimate is conservative but accurate.
Statement III is correct: Well-oxygenated surface water has high dissolved oxygen (DO) (5-10 mg/L, up to 12-15 mg/L in cold, turbulent conditions, per USGS). Atmospheric air contains 21% oxygen (~210,000 ppm, 210 g/L). Surface water’s DO (0.015 g/L) is ~14,000 times less than air, due to low oxygen solubility, confirming it cannot hold "several folds higher" oxygen.