Correct Response: B. When atmospheric carbon dioxide dissolves in seawater, it reacts with the water to produce carbonate and bicarbonate ions. The bicarbonate ions combine with calcium ions as marine invertebrates, such as corals, make their protective shells. This is an important step in the cycling of carbon between the atmosphere and lithosphere because the reef carbonates formed by corals eventually become the extensive limestone deposits of the lithosphere. Carbonic acid produced during the weathering of limestone moves into the hydrosphere not the lithosphere (A). The decay of biomass (C) moves carbon from the biosphere to the atmosphere and atomic carbon is highly reactive and so by itself is not directly absorbed by deep-ocean sediments (D).
