>Calcium cycling provides a link between tectonics, climate, and the carbon cycle. In the simplest terms, uplift of mountains exposes calcium-bearing rocks to chemical weathering and releases Ca2+ into surface water. These ions are transported to the ocean where they react with dissolved CO2 to form limestone (CaCO
3), which in turn settles to the sea floor where it is incorporated into new rocks.

If the oceans are acidifying, why not just introduce robust populations of shellfish near oceanic trenches, where free Ca2+ is abundant, to sequester carbon dioxide as limestone?