Most countries have agreed to set a target to reduce their greenhouse gas emissions. One idea being investigated by scientists is reduce carbon dioxide by a process called carbon sequestration into the oceans. One idea is to try to increase the usual levels of uptake of carbon dioxide by microscopic and unicellular plants collectively called phytoplankton. This would involve, so one theory goes, of seeding the world’s ocean’s with iron (a food for the plankton) which would hopefully increase the productivity of these plants and enable those tiny plant organisms at or near the sea surface to absorb more carbon dioxide so taking it from the atmosphere and storing it in the ocean. There are many doubts about what impact this would have on the marine life and ecosystems and whether it will actually do what the theory predicts.
A second idea of using the oceans for sequestration of carbon dioxide is to inject liquid carbon dioxide into the pecan deeps at 1500m and store it there for several hundred years or for longer periods if put at depths of 300m or more where the density of the liquid carbon dioxide is greater than that of water. This would create a submarine lake in a trench on the seabed, so scientists postulate. There is also the prediction that solid carbon dioxide blocks should be able to be produced which would therefore sink to the bottom of the ocean. There is much concern over the impact of such actions.