ocean acidification

Human emissions of carbon dioxide are currently acidifying the oceans at a rate unprecedented in the last 300 million years — since well before the dinosaurs evolved — according to a study published today in Science. More acidic water can dissolve the shells of many marine organisms, including reef- and shell-building species, such as clams, oysters and corals, as well tiny organisms that form the base of the food chain.

To survive in the ocean, soft-bodied organisms must possess one of five traits: big teeth, toxic flesh, invisibility, quickness or a hard shell. Most marine organisms that employ the latter, called calcifiers, build their hard shells from the mineral calcium carbonate. However, increasing atmospheric carbon dioxide levels are making the oceans more acidic — which, in turn, is reducing the concentration of carbonate ions dissolved in seawater that organisms use to build their protective shells and skeletons.