What causes global O2 levels to rise in spring/summer?

[Hoku]

I'm writing a paper (not homework) and would like to refer to how the entire Earth's O2 levels rise when it's spring/summer in the northern hemisphere. I understand that this happens because most of the Earth's plant life is there. Can anyone please tell me the proper name of this phenomena, or how I should properly refer to it?

 

[Andre]

It's probably a bit more complex with a lot more factors playing a role like sea surface temperatures. This may be a useful publication.

 

[Hoku]

Thanks for the link. I did read through it. The reason it doesn't fully help is because it focuses on regional changes of CO2/O2 based on the local season. It doesn't seem to describe any global increases of O2. The source of my (limited) knowledge is the movie, An Inconvenient Truth. Any other insights or directions people can point me would be deeply appreciated.