An updated assessment of the acute impacts of ocean carbon sequestration by direct injection

摘要

This paper evaluates the expected environmental impact of several promising schemes for ocean carbon sequestration by direct injection of CO_2, and serves as a major update to the assessment by Auerbach et al. (1997) and Caulfield et al. (1997) of water quality impacts and the induced mortality to zooplankton. The impact assessment methodology from the earlier studies has been updated to incorporate the extended probit methodology of Sato et al. (2004), and revised mortality relationships based mainly on copepods were developed after a thorough review of publicly available CO_2 toxicity data for zooplankton and fish. The impact assessment is conducted for three discharge approaches, each designed to maximize dilution over the water column: a point release of negatively buoyant CO_2 hydrate particles from a moving ship; a stationary point release of CO_2 hydrate particles forming a sinking plume; and a long, bottom-mounted diffuser discharging buoyant liquid CO_2 droplets. Two of these scenarios take advantage of the enhanced dilution offered by CO_2 hydrate particles, and are based on ongoing laboratory and field studies on the formation and behavior of such particles (Chow et al., 2008). Overall, results suggest that it is possible with present or near present technology to engineer discharge configurations that achieve sufficient dilution to largely avoid acute impacts. In particular, the moving ship hydrate discharge is identified as the most promising due to its operational flexibility. In addition to lethal effects, sub-lethal and ecosystem effects are discussed qualitatively, though not analyzed quantitatively. The main conclusion from our analysis is that ocean carbon sequestration by direct injection should not be dismissed as a climate change mitigation strategy on the basis of environmental impact alone. Rather, it can be considered as a viable option for further study, especially in regions where geologic sequestration proves impractical.