APES Unit 9.7 (Ocean Acidification)

Ocean Acidification

  • Increased CO2 in atmosphere → increased ocean CO2 (direct exchange)

    • CO2 combines with ocean water to form carbonic acid (H2CO3)

    • Carbonic acid dissociates into Bicarbonate ion (HCO3-) and H+ ion

    • Increased atm. CO2 → increased ocean CO2 → CO2 combines to form carbonic acid → Acid dissociates into Bicarbonate & H+ ion

Calcium Carbonate & Marine Organisms

  • Marine org. that make shells use calcium (Ca+) and carbonate (CO32-) ions to build their calcium carbonate shells (calcification)

    • CO2 increase & ocean acidification makes carbonate ions less available 

      • Carbonic acid → increased H+ ions which bond w/carbonate to form Bicarbonate (HCO3-)

  • Marine shells breakdown as pH decreases and carbonate ions are less soluble in ocean water

  • Fewer carbonate ions = less calcificaiton; weaker shells of coral mollusks, and urchins

Climate Change & Ocean Acidification 

  • Antrhopogenic casuses for ocean acidification: FF combustion (CO2), deforestation (CO2) and coal/gas combustion (NOx/SOx → acid precipitation)

    • CO2 increase directly correlated with ocean acidification

      • Inverse relationship b/w atm. CO2 & ocean pH (low pH = more acidic)

      • Ocean pH has decreased from 8.2 to 8.1 in past 150 years; could decrease to 7.8 by 2100

      • *pH = log scale so 8.2 to 8.1 = 30% decrease