Putting the Concepts into Context: Ocean Carbon Sequestration

Methods to mitigate climate change fall into different categories of readiness, ranging from those already commercially deployed to those concepts which may hold promise but are far from ready. Judging whether a method is likely to have significant deployment, or warrant further research depends on its merits relative to other options in its class of readiness. On this basis, a range of ocean carbon sequestration concepts are compared to other options including other forms of carbon sequestration.

The storage of carbon dioxide captured from large stationary sources would enable coal to continue its important contribution to energy supply, in a greenhouse gas constrained world. Compared with storage in nearby secure geological formations, the ocean storage via carbon dioxide injection in at depth (~3km) appears to: cost more, have shorter carbon dioxide retention, and a present impacts on deep ocean ecosystems that raise barriers to its deployment. Whereas geological storage has been deployed in specific circumstances and is being considered for broad deployment, ocean storage is not being considered for deployment.

There are a number of concepts to enhance ocean uptake of carbon dioxide by strengthening the settling of particulate organic carbon from the ocean surface to the deep ocean, or by strengthening ocean buffering of changes in pH. Introducing the micro-nutrient iron to increase settling has an advantage over concepts that use either bulk nutrients or bulk introduction of buffering agents in that it involves relatively small quantities of iron. A number of experiments and analyses continue to better quantify how effective iron fertilization might be, what is its scope, and what are its effects on ocean ecosystems and ocean chemical environment. Like other geo-engineering concepts, such concepts are not at a state of understanding to consider deployment, but further research could sort out which concepts warrant advancement.