The ocean is a “carbon sink,” which means that it removes CO2 (carbon dioxide) from the atmosphere. The ocean currently absorbs about one-third of the CO2 released by the burning of fossil fuels.
However, beyond a certain level of atmospheric CO2, the ocean can no longer act as a carbon sink without it having a negative impact on marine life. When CO2 dissolves in seawater, it leads to decreased pH levels. The ocean becomes less alkaline. This is referred to as ocean acidification.