1. Ocean Acidification Process GCSE Science

2. Why study ocean acidification? –The oceans contain 50 times more carbon dioxide than the atmosphere –The ocean pH has decreased by 0.1 of a unit, representing a 29% increase in hydrogen ions since the Industrial Revolution –The oceans absorb roughly 30% of human-generated carbon dioxide

3. Why is pH? –pH is the unit used to measure acidity –The lower the pH value, the greater the acidity GCSE Science Increasing acidity 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Drain cleaner Ammonia Soap Baking soda Water Milk Banana Tomato Vinegar Lemon Hydrochloric acid

4. Atmospheric CO2 CO2 dissolves in water CO 2 (aq) Carbon dioxide in the atmosphere dissolves in the oceans. Ocean acidification process

5. Atmospheric CO2 CO2 dissolves in water Forms Carbonic Acid CO 2 (aq) This aqueous carbon dioxide reacts with the water to form carbonic acid. H 2 CO 3 Ocean acidification process

6. Atmospheric CO2 CO2 dissolves in water Forms Carbonic Acid Breaks down to form bicarbonate and hydrogen ions CO 2 (aq) H+H+ HCO 3 - The carbonic acid breaks down to form bicarbonate and hydrogen ions. The increase in hydrogen ions makes the oceans more acidic. So the more carbon dioxide that is absorbed by the oceans, the more acidic they become. H 2 CO 3 Ocean acidification process

7. Atmospheric CO2 CO2 dissolves in water Forms Carbonic Acid Breaks down to form bicarbonate and hydrogen ions Carbonate ions react with these ‘extra’ hydrogen ions CO 2 (aq) H+H+ HCO 3 - CO 3 2- + Carbonate ions ‘buffer’ this increased number of hydrogen ions by forming more bicarbonate ions. Carbonate ions enter the oceans through processes such as the weathering of limestone (CaCO 3 ). This buffering decreases the amount of carbonate and hydrogen ions in the oceans. H 2 CO 3 Ocean acidification process

8. Atmospheric CO2 CO2 dissolves in water Forms Carbonic Acid Breaks down to form bicarbonate and hydrogen ions Carbonate ions react with these ‘extra’ hydrogen ions CO 2 (aq)H 2 CO 3 H+H+ HCO 3 - CO 3 2- + Ocean acidification process Organisms that form their shells or skeletons from carbonate will be affected because there are fewer carbonate ions in the oceans. The levels of ocean acidification may also reach a ‘corrosive’ level where these shells or skeletons start to dissolve to ‘buffer’ the ocean pH.