Interactions of Co2 with Sedimentary Blue Carbon: The Fate of Leaked Co2 from a Geological Storage Site

Abstract

A main consideration for carbon dioxide removal is the net carbon storage potential i.e. whether the amount of stored carbon, significantly outweighs the carbon footprint of the storage process. Here we assess the potential for disruption of blue carbon stored in sediments, and interactions of leaked CO2 with that sedimentary blue carbon, experimentally, above a sub-seafloor geological CO2 storage site in the North Sea. North Sea sediments contained minimal organic carbon but a significant variable fraction of biogenic inorganic calcite (PIC). Bubbling experiments showed that leaked CO2 titrated away the CO32- ion in seawater to drive under-saturation with respect to calcite until equilibration occurs between the CO2 stream and the calcite. Sites abundant in PIC face a risk of blue carbon depletion in the event of leakage, but have potential for re-sequestration of escaped CO2 into solution, as a result of enhanced dissolution of seafloor calcium carbonates releasing alkalinity. Aqueous storage of any released CO2 will be limited under low rates of release, due to the titration of the carbon dioxide with the alkalinity already present in the sediment pore water. At higher release rates the re-sequestration of the escaped CO2 is controlled by the solubility of the calcium carbonate under near CO2 saturated conditions. Particulate organic carbon (POC) rich sites exhibit a reduced susceptibility to blue carbon loss, yet have a reduced neutralization potential for CO2 leakage.

Keywords: Sedimentary Blue carbon, geological carbon storage, leakage risk, calcium carbonate, buffering, dissolution, alkalinity, carbon dioxide