What's ocean acidification?

You may remember learning about acids and bases in high school. Every liquid is either acidic, basic, or neutral. You can measure this by measuring its pH: a neutral liquid has a pH of 7; anything over 7 (up to 14) is basic while anything under 7 (down to 0) is acidic.

oh, litmus tests! who didn't love these?

Say you have something with a pH of 8 but you want it to have a pH of 5. You can simply add an acid, or anything that's going to give up its hydrogen ions, because pH is just a measure of hydrogen ions in a solution. By adding acid, or acidifying the solution, you will lower the pH.

lots of hydrogen ions (in red) = acidic solution
lots of hydroxide ions (in blue) = basic solution

So, back to the main question: what's ocean acidification? It's when the ocean's pH gets lowered by the increase of hydrogen ions. The increase of hydrogen ions is from increased atmospheric CO₂. The ocean will absorb the CO₂, which will become aqueous and react with water (H₂O) to create carbonic acid. It doesn't stop there; carbonic acid can give up its hydrogen ions to become bicarbonate and then carbonate ions.

uptake of carbon dioxide into the ocean can
result in increased hydrogen ions (circled in red)

Where all this gets tricky is that organisms will use carbonate ions to make calcium carbonate (CaCO₃), but if there is extra hydrogen ions floating around, the carbonate ion will bond to them. Briefly, acidified ocean water becomes corrosive to calcified organisms.

spider crab larva: "Aren't I pretty?

All my little spines are made from calcium carbonate!"

How does this affect crabs? Stay tuned for research being performed in Alaska on larval crab development in acidified sea water (coming this Friday, March 9th)!