Evaluation of the environmental viability of direct injection schemes for ocean carbon sequestration

Abstract

This thesis evaluates the expected impact of several promising schemes for ocean carbon sequestration by direct injection of CO2, and serves as an 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 present work extends the methodology used in the earlier studies, incorporates recent acute CO2 toxicity data on marine organisms, and considers three revised discharge approaches: a point release of negatively buoyant CO2 hydrate particles from a moving ship; a long, bottom-mounted diffuser discharging buoyant liquid CO2 droplets; and a stationary point release of hydrate particles forming a sinking plume. Results suggest that it is possible with present technology to engineer discharge configurations which achieve sufficient dilution to largely avoid acute impacts. Sub-lethal and ecosystem effects are discussed qualitatively, but not analyzed quantitatively. The analysis suggests that, as a temporary climate change mitigation strategy, ocean carbon sequestration by direct injection should not be dismissed on the basis of environmental impact alone. With minor modification, this thesis will also serve as the final chapter of the author's Ph.D. thesis to be submitted in 2008 to the MIT Department of Civil and Environmental Engineering.