What is Ocean Acidification ?
Ocean acidification is the process resulting from the decrease in the pH of the Earth's oceans caused by the uptake of carbon dioxide from the atmosphere. When carbon dioxide from the atmosphere is absorbed by oceans, is created carbonic acid in the waters.
This is a serious environmental problem because, like trees, the oceans play the role of the planet's lungs or natural carbon sinks, which, when acidified, cause death and disease of marine species fish, corals, plankton... with the consequent detriment to marine biodiversity and the intensity of global warming.
More information:
https://www.dfo-mpo.gc.ca/oceans/publications/soto-rceo/2012/page02-eng.html
https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F