More research needed

ScienceDaily: Global Atmospheric Carbon Level May Depend Primarily On Southernmost Ocean

The article above is about the importance of the cold southern oceans around Antarctica in taking up CO2.

It also mentions an idea for increasing carbon sequestration that has been around for a long time, but doesn't seem to get raised much lately:

"In the Antarctic, the circulation pattern moves the surface water carrying carbon dioxide deep into the ocean's depths, where the sequestered carbon could potentially be trapped for a long time," Marinov said. "According to the models we used, the deep Antarctic is the critical region where we need to concentrate our research."...

"An interesting idea of recent years is that we can sequester a lot of carbon if we dump iron into the ocean to encourage the growth of certain microorganisms, which incorporate carbon as they grow," Marinov said. "These organisms would then fall to the ocean floor after they die, taking the carbon with them. The overall effect would be to lower concentration of carbon in the surface waters, allowing more atmospheric carbon dioxide to dissolve into the sea. Our research has implications for future iron fertilization experiments, the focus of which we conclude should shift to the Antarctic."

I seem to recall that they have done small scale trials of this to check the effectiveness. Ah yes, I am correct. (The linked site seems entirely devoted to promoting the idea, which is somewhat controversial. Seems worth looking into further, though.)