Rancid wrote:The problem is the excess CO2, not the lack of oxygen. When there is more CO2, you get more carbonic acid in the oceans (the same stuff that's in sparkling water). When you have CO2 in the precense of water, the CO2 dissolves into the water and makes it more acidic. You can notice this if you leave a glass of water open over night. Then try drinking it in the morning, you will notice the water tastes different (people describe it as stale water). This is because of the carbonic acid that has formed.
That acidity kills the organism in the ocean that convert CO2 into O2. If they die off, the acidification process accelerates. It's a run away effect (in science and enigneering, it's called a positive feedback system. Something that accelerates and encourages itself the more it happens).
The logic is good, the reality isn't. CO2 is making the sea more acidic but it is still pH 8 and would take a hell of a lot to make it pH7 or less.
The maths is as follows pH 8 with a hardness of 8-12kH (typical sea water) gives dissolved CO2 between 2 & 4 ppm. To drop the pH to neutral 7pH without reducing hardness requires a tenfold increase in CO2 and we are a very long way from that.
The problem is that many of these small organisms form an exoskeleton of calcium carbonate by absorbing from the sea. The less alkaline the ocean, the harder it becomes to form a shell as it has been used to neutralise the carbonic acid. This kills the life that larger organisms depend on.
The algae that convert CO2 to O2 by photosynthesis do not form shells. They thrive in warm conditions with plenty of CO2. If the seas become oxygen deprived it will change what algae grows and that is a problem as red and blue-green algae give off toxins that kill wildlife, cover the surface and block light to the photosynthesising life below.
I know all about carbonic acid, I use fire extinguishers to dose the plants in my aquariums. I increase the CO2 from 4ppm to 35ppm and none of the plants or animals die. Push it to 50ppm and my fish would be gasping at the surface, while my plants would eat through the other nutrients in the tank at an unsustainable rate. If I did nothing about it then the fish would die and an algal bloom would finish off the plants as they start cannibalise themselves as a means of providing nutrients for further growth and leach ammonia into the water.