50% of the oxygen comes from the sea
50% of the oxygen in the earth's atmosphere comes from the sea. It is above all the plant plankton in the sea, which absorbs CO2 and converts it via photosynthesis into carbohydrates such as sugar or starch. This results in the splitting of water - almost as a waste product - oxygen. The more CO2 gets into the sea via the atmosphere and the sea surface, the more the plant plankton absorbs, after all, CO2 acts like a fertilizer. In other words, the more CO2 there is, the more plant plankton grows.
CO2 in water becomes carbonic acid
But this process can not be continued indefinitely - otherwise the pollution of the atmosphere with CO2 would not be a problem thanks to the sea as a "cleaner". Then the phytoplankton could easily turn everything into biomass and oxygen. But this is not the case. At a certain point, phytoplankton lack other substances to grow, such as iron or certain minerals, and so not all CO2 can be converted.
As soon as the excess CO2 dissolves in the water, it becomes carbonic acid and thus affects the ph value of the seawater. It is often said that the sea would then "sour", which is not true in principle. Seawater is basic, its acidity shifts through the carbonic acid in the direction of "sour". Correctly, it will then be "less basic" because it is still on the ph scale in the basic range and is far from "sour". However, it has been shown that sea ph has dropped 0.05 to 0.1 points over the last 200 years, depending on the location.
CO2 causes the sea level to rise
However, when the sea does not cope with CO2, the CO2 content in the atmosphere increases, which in turn means that the sun's infrared rays that enter the Earth's atmosphere can no longer escape. This creates the greenhouse effect and air and water heat up. And when water warms, it expands, causing a rise in sea level. What can be catastrophic in the face of the many people living near the coast.
If we compare the oxygen production of the sea with that on land, we immediately realize the importance of the oceans: Let us only imagine how much we have already cut down the large forest areas on earth, that is, how strong the oxygen production on land already restricted. The size of the sea is therefore an extremely important source of oxygen to which, for our own benefit, we should take care. The solution can only mean: use less CO2. For example, fly less, eat less meat (the mammalian CO2 consumption is enormous) and do not heat unnecessarily in winter.