Metal mobility in sub-sea bed sediments during and after a temporary carbon dioxide leak

Abstract:

Carbon Capture and Storage (CCS) is a technology that has the capacity to mitigate anthropogenic carbon dioxide release. However, the environmental impact of a leak of carbon dioxide gas from a sub-seabed CCS facility is, as yet, only partially understood. A field scale experiment was set up to simulate such a leak and investigate the environmental, geophysical and biogeochemical responses to a loss of containment in a CCS facility. Many findings were presented at the AGU Fall Meeting 2013 by Blackford et al, Lichtschlag et al, Cevatoglu et al and Taylor et al, among others. These new data add further to our understanding of the environmental impact of a sub-sea bed leak of carbon dioxide.

During the simulated loss of containment from a CCS facility, carbon dioxide migrated through the sea floor sediments, reducing sediment pH and increasing the dissolved inorganic carbon content of the pore water. Both of these factors can change the solubility of trace metals in the sediment pore water, increasing their mobility and potentially affecting the flux between the sediment and the overlying sea water. Over-abundance of certain trace metals in the natural environment, such as Cu, As or Pb could have severe long-term implications for the fauna exposed to such an environment, due to their toxicity. During the release experiment, Diffusive Gradient in Thin-film (DGT) probes were deployed into the sediment. These gel and resin probes were placed across the sediment – water interface for 24 hours. They were then analysed using mass spectrometry with laser ablation, producing a high resolution vertical profile of metal concentration in the sediment and into the overlying water. On every deployment occasion, probes were deployed at the carbon dioxide release epicentre and at a reference zone, some 450 m distant. Probes were deployed numerous times during the experiment, providing information on the baseline conditions, the impact of carbon dioxide release and the rate of recovery to more normal conditions. The results from these deployments will be displayed, showing the impact of carbon dioxide migration on the mobility of dissolved metals in sediment pore water during the simulation of a leak from a CCS facility in the natural environment