Just out of interest how much free oxygen is there in seawater?
This one is rather long, but as it's a subject I'm interested in too?
Read it at your peril :)
There are areas that have no free oxygen at all, and they are growing as as we use 'nutrients' as fertilizers that follows the groundwater and streams into the oceans. "The largest dead zone covered 70,000 square kilometres (27,000 mi˛). A 2008 study counted 405 dead zones worldwide." From Dead zones.
Add to that the accumulation of man-made CO2 in the oceans introducing acidity and further heating of the oceans, freeing even more oxygen (and C02) from the surface, and also reducing its capacity to take up atmospheric CO2. The greatest uptakes of CO2 and oxygen comes from the cold water in the arctic and antarctic and those uptakes have been reduced significantly according to measurements made by several researchers.. Ocean acidification.
Then there is one point more. I don't know how the increased accumulation will change the chemistry of the oceans, that is how much we can expect it to accumulate, it also depends on if the salinity and temperature and that changes with the underwater circulation and streams, as/if the warming disrupts them, and change their revolutions around the globe.
For example, we have streams transporting oxygen-full cold water from both the arctic and the antarctic to our warmer waters, they also bring with them krill etc which is the basis for the marine food chain. Would they to change you will find a accelerating scenario with fish death and more oxygen free areas, as a guess. Also it will heat the oceans even further and just as a hot soda-can almost will explode if left to long in the sun so the ocean then will free both CO2 and oxygen creating an even more unhealthy environment for marine life.
Then we come to the oxygen in the atmosphere. It seems to be falling according to Professor Ralph Keeling from Scripps Institute.
The Keeling curve from climatecentral.
What control the distribution of carbon in the oceans are called the 'solubility pump' and the 'biological pump'. Cold polar waters contains double the amount of CO2, as compared to the warmer waters (tropical) and their streams, like our gulf stream, are the mechanisms for distributing it into the cold denser depths of the oceans, that then can hold greater amounts for a very long time, assuming that those depths don't get warmed up too that is. The 'biological pump' is made out of plants (phytoplankton) that needs the CO2 for convertion. They mostly grow close to the surface as they also need the sunlight. They are the main food for zooplankton that in its turn becomes the food basis for krill, and so are the start of the marine food circle.
There are some that expect CO2 to help our flora/fauna to grow, but that is a very delicate balance. Take a look here
if you're interested about the newest finds. Another thing about the acidification of our oceans is that it seems to kill of the reproductivity of several species of marine life, according to Jonathan Havenhand at the University of Gothenburg in Sweden.
"Experiments show that the struggle by copepods, snails, sea urchins and brittlestars to balance the changing pH inside their bodies impairs their ability to reproduce and grow. Many species are unlikely to genetically adapt to ocean acidification, because the change is occurring too quickly." So it's not only coral reefs 'withering away/dissolving' here.
Heh, too long by far huh :)