1. CO₂ absorbed by seawater (H₂O).

2. CO₂ reacts to form carbonic acid; makes water more acidic (more hydrogen atoms).

3. Carbonic acid breaks down into bicarbonate and hydrogen ions (H⁺). Bicarbonate breaks down into more H⁺ and carbonate, key to organisms like oysters, clams, corals, and other marine organisms that make shells and skeletons. But as acidity increases, less bicarbonate changes into carbonate.

Higher CO₂ causes shells to dissolve.

Calcium carbonate is the main building block in the shells of marine animals. As seawater becomes more acidic, calcium carbonate — and the shells — can dissolve.

In an estuary like the Chesapeake Bay, sources other than the atmosphere — like runoff of excess nutrients — may add additional CO₂ to the water, contributing to acidification. Evidence suggests that higher acidity in the Bay could slow the rate of growth in the shells of young oysters, making them thinner and more vulnerable to predators.