The absorption of man-made CO2 emissions by the ocean has substantially lowered the seawater pH
and the concentration of carbonate ion - a process called Ocean Acidification. The availability of carbonate ions is crucial for marine calcifying organisms to form their skeletons or shells that are made of crystalline forms of calcium carbonate.
Under present-day conditions the surface waters of the ocean are supersaturated with respect to calcium carbonate creating conditions favorable for marine calcifying organisms. With increasing depth the level of saturation decreases as a result of increasing carbon concentration and higher pressure. At the so called "aragonite saturation depth" the water becomes undersaturated with respect to this form of calcium carbonate which means that shells and skeletons made of aragonite near the surface start to dissolve. The animation focuses on the Southern Ocean. The Southern Ocean is subject to a large seasonal cycle in acidity that brings waters low in calcium carbonate to the surface. Thus it is particularly vulnerable to experience chemical conditions that are adverse to calcifying organisms as the combination of a large annual cycle on top of the man-made trend can lead to an earlier undersaturation of surface waters with respect to calcium carbonate. The animation shows a projection of how the aragonite saturation depth is going to shoal in the 21st century as a result of man-made carbon dioxide emissions. As you can see, surface waters of the Southern Ocean are projected to experience undersaturation by the year 2030 with potentially severe consequences for the marine ecosystem.