I was looking through the petitions on petitiononline.com and one guy created a petition, asking Bill Gates to buy all the world’s rain forests for some $26 billion so that people can have fresh air to breathe for years to come.
I thought the oceans were the greatest source of clean oxygen on this planet. Is this true?
Trees and green plants take in carbon dioxide and put out oxygen. So they help clean up the major greenhouse gas plus give us oxygen to breathe. As for the oceans putting out oxygen, I’ve never heard that.
This tells the answer. It is a good thing since Gates would have a problem buying all the oceans. 
Well, the water in the oceans wouldn’t produce any oxygen, but the phytoplankton would be at least a major contributor. There’re probably two reasons they don’t get much publicity: First, rainforests are prettier, and second, there isn’t the same wholesale threat to phytoplankton as there is to the rainforests.
Thanks, Chronos, I knew about the phytoplankton but was taking the easy way out. Your post made me look it up and it seems that the oxygen they produce is at least important in the first case in providing oxygen for the fish and plants in water. There is also a portential problem since during the night when photosynthesis is not going on, they consume some of the oxygen themselves.
I find that link a bit dubious as a reliable source. I won’t claim any of it is an outright lie but it is certainly misleading in many places. Can you say “agenda”? Of course, this is a bit OT but I would seek a more…uhmm…balanced view for the info being sought in the OP.
My guess would be that the oceans are far more important (which is not to say that the rainforests aren’t important). I don’t know how much oxygen the ocean generates but I thought they were huge carbon sinks. Also, remember that long before rainforests our atmosphere was much different than it is today (downright toxic to humans). It was the oceans that cleaned it all up and ultimately set the stage for plants and animals to colonize the land. That again would suggest to me that oceans trump rainforests.
Just look at the carbon cycle. While trees do take in CO2 and release O2 they really only borrow it. When they die and either rot or burn every last part of the C that the tree has taken in is re-released.
Oceans also have plants that take in CO2 and release O2 then re-release that C when the die also but the ocean has 2 more things going for it:
1 the ocean, since it holds disolved gasses an moderate the change in concentration of gas in the air
2 the ocean is the only CO2 sink. CO2 in the oceans are converted into rock (IIRC limestone) - never to be released again.
But carbonate rocks are a sink of both carbon and oxygen. It’s important in that it removes carbon dioxide from the atmosphere so that Earth doesn’t end up with an atmosphere like Venus’s, but it’s not how atmospheric oxygen is created.
The oceans are a sink of just carbon in another way. Phytoplankton and other oceanic microorganisms generate hydrocarbon molecules which they keep within their cells. Some of these plankton eventually end up buried in the sediment on the ocean floor.[sup]1[/sup] This separates those carbons from atmospheric oxygen for the long term.
Land plants that fall into water and get buried also provide a net long term separation of oxygen and carbon.[sup]2[/sup] But that doesn’t happen with most trees. In fact, in tropical rainforests, most trees that fall are quickly devoured by molds and insects. By quickly, I mean just a few months, rather than the years this process takes in temperate forests.
[sup]1[/sup] If they get buried deeply enough, you get oil.
[sup]2[/sup] Ditto for coal.