You are incorrect, madam

Well my dears, it seems that I have steered you wrong (as per our discussion earlier in the week). To recap things, I was given some questions in one of my classes and chose to discuss the changing pH in the world’s ocean and how it relates to the uptake of CO2. I was of the opinion that this was a sneaky question seeing as the pH of the ocean is changing as we speak due to how seawater reacts with atmospheric CO2. While this isn’t totally incorrect (you like that double negative?), it’s not the answer that the proff was looking for. Turns out that the correct answer is that the world’s oceans have had a relatively constant pH since the last ocean anoxia event 10s of millions of years ago.

Ocean Anoxia Events (OAEs) are times in the earth’s history where the deep oceans lost most, if not all, of its dissolved oxygen. Lots of very smart people are spending very large amounts of money to figure out why these events occur because nobody has a straight answer just yet.

This is what an OAE is like: You ever been swimming in a lake? Chances are good that if you went in the summer, the upper couple of meters was nice and comfy; but if you swam (swum? swimmed?...oh, forget it) deeper you’d hit a boundary, below which the water gets really really cold. That boundary is called the thermocline and exists not just in lakes, but in oceans too.

thee thermocline

The effects of sunlight can only be felt, at most, 60 to 100 meters deep. We call this layer the surface ocean. Everything below it is considered the deep ocean. The surface ocean and deep ocean don’t transfer water that easily. Upwelling and downwelling are pretty much the only ways the water "communicates". All that warm stuff on top wants nothing to do with the cold and salty stuff on the bottom. The only way to mix them is via ocean currents that move various bodies of water all around the earth through the deep sea.

During Ocean Anoxia Events, the world’s oceans become a lot like that lake. Communication between the surface and the deep is cut off, which limits the input of dissolved oxygen to the deep ocean. Without that input, all the fishes, and jellyfishes, and sharks, and shrimps, and crabs, and microorganisms that live in the deep sea eventually “breathe” up all the available oxygen until there is no more. No more oxygen = no more life = mass extinctions.

The chemistry of deep waters gets really screwy when all the oxygen is gone. Chemicals like hydrogen sulfide appear in the deep sea and we get a condition that is known as “euxinic”. These conditions are bad, bad, bad for the life that we know and love but great for organisms that thrive in low oxygen conditions. So, to bring all this back home to the question of pH, yes, the pH of the world’s oceans has remained relatively constant for a long long time. That being said, I'm going to stand my ground and say that I wasn’t totally wrong. Meh, whatevs. "A" for effort, right?