What phenomenon occurs when the ocean absorbs excess anthropogenic carbon dioxide () from the atmosphere, forming carbonic acid and reducing seawater pH and carbonate ion concentrations?

Answer and explanation

Correct answer: C. Ocean acidification

  1. Step 1: The global oceans have absorbed approximately 25-30% of all anthropogenic carbon dioxide emissions since the Industrial Revolution.
  2. Step 2: When dissolves in water, it forms carbonic acid (), which dissociates to release hydrogen ions (); these ions bind with carbonate ions (), depleting the building blocks calcifying organisms (corals, pteropods, shellfish) require to build calcium carbonate shells.
Answer
Ocean acidification
Why not the others: 'Ocean deoxygenation' Ocean deoxygenation is the decline in dissolved oxygen concentrations in marine waters due to ocean warming and eutrophication; 'Thermal expansion' Thermal expansion is the physical increase in the volume of seawater as its temperature rises, contributing to sea-level rise; 'Upwelling' Upwelling is the oceanographic process where winds drive surface waters away, drawing nutrient-rich cold deep water to the surface.

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