Efficiency of Sequestrating CO 2 in the Ocean

1. Efficiency of Sequestrating CO2 in the Ocean Gilbert Stegen SAIC/GRS Associates, Redmond WA Dr_Stegen@hotmail.com and Richard Dewey University of Victoria, BC, Canada RDewey@uvic.ca NETL May 2001

2. Sequestration EfficiencyStegen and DeweyOcean Sequestration • The Ocean is a natural sink for Atmospheric CO2, including anthropogenic CO2 emissions. • Ocean Sequestration would accelerate that natural process and reduce the rate of build-up of Greenhouse Gases in the Atmosphere. • Regardless of the initial sink (either Atmosphere or Ocean), the long term equilibrium between these reservoirs will partition the CO2 12% Atmos - 88% Ocean NETL May 2001

3. Sequestration EfficiencyStegen and DeweySequestration Efficiency Defined • If Ocean Sequestration is to be considered a viable mitigation strategy, it must be demonstrated to be efficient. • Following Orr et al. (2000), we define the Injection Efficiency as the fraction of sequestered CO2 that remains in the ocean: NETL May 2001

4. Sequestration EfficiencyStegen and DeweyPrevious Studies • To date studies have included modelling, laboratory, and more recently in situ injection experiments (i.e. Brewer et al, 2000). • In general, these studies have consistently found that improved, long-term ocean sequestration is more probable when: • the injection depth is increased • the CO2 remains away from regions of vertical advection and/or mixing (e.g. convection). NETL May 2001

5. Sequestration EfficiencyStegen and DeweyEfficiency and Advection/Diffusion • Can we identify regions in the ocean that may have “efficient” sequestration characteristics based on regional oceanic properties? • Dispersion in the ocean is governed by the Advection/Diffusion equation. • Low dispersion will result in “confined” regions of injected CO2, and minimize venting of injected CO2 back into the atmosphere. NETL May 2001

6. Sequestration EfficiencyStegen and DeweyOcean Properties Affecting Diffusion NETL May 2001

7. Sequestration EfficiencyStegen and DeweyGlobal Map of Bathymetry NETL May 2001

8. Sequestration EfficiencyStegen and DeweyGlobal Map: Horizontal Velocity NETL May 2001

9. Sequestration EfficiencyStegen and DeweyGlobal Map: Vertical Velocity NETL May 2001

10. Sequestration EfficiencyStegen and DeweyGlobal Map: Vertical Stratification NETL May 2001

11. Sequestration EfficiencyStegen and DeweyGlobal Map: Horizontal Stratification NETL May 2001

12. Sequestration EfficiencyStegen and DeweyA Proxy for Ocean Mixing • How do we get a global map of the distribution of ocean mixing? • WHOI’s Microstructure and Tracer Release groups have identified the interaction of barotropic tides and rough topography. • Global tidal models (Jayne and St.Laurent) with high resolution bathymetry (Smith and Sandwell) can provide global maps of turbulent energy dissipation () associated with topography. NETL May 2001

13. Sequestration EfficiencyStegen and DeweyGlobal Dissipation from Tidal Model NETL May 2001

14. Sequestration EfficiencyStegen and DeweyComposite Sequestration Efficiency • The resulting 3-dimensional field of Ocean (composite) Sequestration Efficiency can be constructed as a weighted sum of the normalized ocean properties. • This composite field is 4-dimensional, varying in space (x,y,z) and time (seasonal). NETL May 2001

15. Sequestration EfficiencyStegen and DeweyMaximum EC in Water Column NETL May 2001

16. Sequestration EfficiencyStegen and DeweyMinimum EC in Water Column NETL May 2001

17. Sequestration EfficiencyStegen and DeweyUse MODM to Estimate Injection Efficiency • We can use the Mesoscale Ocean Dispersion Model (MODM) to estimate the Injection Efficiency of various sites. Eddy resolving, ½°, Lagrangian particle tracking. • 1) South-East of Tokyo • 2) South-East of New York • Simulate CO2 injection for 150 years NETL May 2001

18. Sequestration EfficiencyStegen and DeweyMODM NW Pacific: Ei at 500m and 1000m NETL May 2001

19. Sequestration EfficiencyStegen and DeweyMODM NW Atlantic: Efficiency at 500, 1000, 1500, 3000m Efficiency=(CO2 in Ocean/CO2 injected) % NETL May 2001

20. Sequestration EfficiencyStegen and DeweyConclusions • To first order, a global composite map of Ocean Sequestration Efficiency can be estimated from global oceanic fields. • The real Ocean is highly variable in space and time, and the role of sub-grid scale processes not typically resolved by OGCMs is critical in predicting ocean sequestration efficiency. • Need: very high resolution models (1/10°) with seasonal forcing and Lagrangian tracking. NETL May 2001

21. Sequestration EfficiencyStegen and Dewey Gilbert Stegen GRS Associates, Redmond WA Dr_Stegen@hotmail.com Richard Dewey University of Victoria, BC Rdewey@uvic.ca NETL May 2001

22. Sequestration EfficiencyStegen and DeweyExtra Slides • Minimum Composite Sequestration Efficiency • Brazil Basin Diffusivity • CO2 plume from NY injection at 1000m • Particle distributions for NY injection at 500, 1000, 1500 and 3000m. • Projections (looking): • down • north • west NETL May 2001

23. Sequestration EfficiencyStegen and DeweyMinimum Composite Efficiency NETL May 2001

24. Sequestration EfficiencyStegen and DeweyBrazil Basin Diffusivity (WHOI) NETL May 2001

25. Sequestration EfficiencyStegen and DeweyMODM Simulation: NW Atlantic at 1000m MODM (seasonal, eddy resolving ½°, Lagrangian tracking). Injection at 500, 1000, 1500, 3000m for 150 yrs NETL May 2001

26. Sequestration EfficiencyStegen and DeweyMODM: NWA 4 depths (500,1000,1500,3000) NETL May 2001

27. Sequestration EfficiencyStegen and DeweyMODM: NWA View Looking North NETL May 2001

28. Sequestration EfficiencyStegen and DeweyMODM: NWA View Looking West NETL May 2001