Ocean acidification
Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of carbon dioxide () from the atmosphere. The main cause of ocean acidification is the burning of fossil fuels. Seawater is slightly basic (meaning pH &gt; 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH &lt; 7). The concern with ocean acidification is that it can lead to the decreased production of the shells of shellfish and other aquatic life with calcium carbonate shells, as well as some other physiological challenges for marine organisms. The calcium carbonate shelled organisms can not reproduce under high saturated acidotic waters. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes. Some of it reacts with the water to form carbonic acid. Some of the resulting carbonic acid molecules dissociate into a bicarbonate ion and a hydrogen ion, thus increasing ocean acidity (H+ ion concentration).