Similar to mineralization processes that take place within rocks, mineralization can also occur under the sea. The rate of dissolution of carbon dioxide from atmosphere to oceanic regions is determined by the circulation period of the ocean and buffering ability of subducting surface water. Researchers have demonstrated that the carbon dioxide marine storage at several kilometers depth could be viable for up to 500 years, but is dependent on injection site and conditions. Several studies have shown that although it may fix carbon dioxide effectively, carbon dioxide may be released back to the atmosphere over time. However, this is unlikely for at least a few more centuries. The neutralization of CaCO, or balancing the concentration of CaCO on the seafloor, land and in the ocean, can be measured on a timescale of thousands of years. More specifically, the predicted time is 1700 years for ocean and approximately 5000 to 6000 years for land. Further, the dissolution time for CaCO can be improved by injecting near or downstream of the storage site.
In addition to carbon mineralization, another proposal is deep sea sediment injection. It injects liquid carbon dioxide at least 3000 m below the surface directly into ocean sediments to generate carbon dioxide hydrate. Two regions are defined for exploration: 1) the negative buoyancy zone (NBZ), which is the region between liquid carbon dioxide denser than surrounding water and where liquid carbon dioxide has neutral buoyancy, and 2) the hydrate formation zone (HFZ), which typically has low temperatures and high pressures. Several research models have shown that the optimal depth of injection requires consideration of intrinsic permeability and any changes in liquid carbon dioxide permeability for optimal storage. The formation of hydrates decreases liquid carbon dioxide permeability, and injection below HFZ is more energetically favored than within the HFZ. If the NBZ is a greater column of water than the HFZ, the injection should happen below the HFZ and directly to the NBZ. In this case, liquid carbon dioxide will sink to the NBZ and be stored below the buoyancy and hydrate cap. Carbon dioxide leakage can occur if there is dissolution into pore fluid or via molecular diffusion. However, this occurs over thousands of years.