Peter Köhler 1 October 2015 Dissolution of olivine (potential, side effects) in simulated CO 2 removal experiments enhanced weathering, ocean alkalinization, ocean fertilization Peter Köhler, Judith Hauck Christoph Völker, Dieter A. Wolf-Gladrow Oxford Greenhouse Gas Removal Conference (30 Sep - 02 Oct 2015)
Olivine is: foto: H Grobe (AWI) (0) Basics: Olivine a silicate (Si) containing mineral ((Mg,Fe)2 SiO4 ). found in dunite, one of the major constituents of the Earth s upper mantle and accessible at the Earth s surface. highly dissolvable compared to other silicate minerals. dissolves within 1-2 yr if grinded to 10 30 µm. contains a Mg:Fe molar ratio of about 9:1. Peter Köhler 2 October 2015
Peter Köhler 3 October 2015 (0) Basics: Silicate (olivine) Weathering (Ruddiman 2001) Picture on natural weathering from Textbook W.F. Ruddiman (2001) Earth s Climate, past and future W H Freeman & Co missing due to copyrights. Weathering: input of HCO 3 (+DIC, +alkalinity) and of nutrients into ocean. All C in silicate weathering has its source in atmospheric CO 2. (sum of C in atmosphere-ocean stays constant) Enhance natural weathering by 10 : from < 0.2 to > 1 Pg C yr 1
Peter Köhler 4 October 2015 (0) Basics: CO 2 in Seawater (following Zeebe & Wolf-Gladrow 2001) surface ocean alkalinity [ mol kg -1 ] 2450 2400 2350 2300 2250 100 200 250 Contour lines of pco 2 [ atm] 350 450 P 550 650 750 850 950 150 Z M X Y 300 400 500 600 700 800 900 1000 1950 2000 2050 2100 2150 surface ocean DIC [ mol kg -1 ] 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 P: preindustrial M: modern Y: future X: pure weathering input of HCO 3 Z: net weathering no change in DIC
(1) Potential: Process changes carbonate system CO 2 removal potential 20% smaller (Köhler et al., 2010) Peter Köhler 5 October 2015 (Mg,Fe) 2 SiO 4 + 4 CO 2 + 4H 2 O 2 (Mg,Fe) 2+ + 4 HCO 3 + H 4SiO 4 olivine + carbonic acid cations + bicarbonate + silicic acid Theoretical limit of chemical effect (no enhanced biology): 1 mol olivine removes 4 mol CO 2 (1 t olivine = 1.25 t CO 2 (0.34 t C)) Realization: about 20% smaller depending on carbonate chemistry CO 2 : Olivine [Pg:Pg] 1.4 1.3 1.2 1.1 1.0 0.9 0.8 theoretical limit pco 2 = 385 pco 2 = 700 atm atm 0 1 2 3 4 5 6 7 8 9 10 Sequestered CO 2 [ atm] 0.35 0.3 0.25 C : Olivine [Pg:Pg]
(2) Dissolution Kinetics: Only particles of 1µm sink slow enough for surface dissolution. Peter Köhler 6 October 2015 r diss (%) 100 90 80 70 60 50 40 30 20 10 (c) 0 10-1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 910 d grain ( m) global mean dissolution as function of grain size Dissolution = f (SST, mixed layer depth) Example for grains of 1µm. (Köhler et al., 2013)
(3) Chemistry: CO 2 removal dominated by alkalinization with add-on by silicate fertilization. Peter Köhler 7 October 2015 changes oceanic CO 2 uptake (Pg C yr -1 ) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 3 Pg olivine dissolution per year S1 (silicic acid+alkalinity input) S2 (only silicic acid input) S3 (only alkalinity input) 0.25 0.15 0.05 0.0 0.0 2000 2002 2004 2006 2008 2010 Time (yr) Silicic acid input (ocean fertilization) increases CO 2 removal by 8%. (Köhler et al., 2013) 0.3 0.2 0.1 normalized (Pg C yr -1 per Pg olivine)
(4) Marine Biology: Enhanced olivine dissolution is also ocean fertilization, leading to species shifts. Peter Köhler 8 October 2015 Silicic acid input from olivine dissolution species shift Diatom NPP: + 14%; organic C export: + 1% (Köhler et al., 2013)
(5) Iron: Iron fertilization (+50% CO 2 removal) is possible but less feasible. Peter Köhler 9 October 2015 Already a dissolution and biological availability of 1% of the iron contained in olivine leads to iron saturation. Iron fertilization is restricted to HNLC areas, mainly in Eq Pac (model-dependent) and the Southern Ocean. (up to) 0.55 gc per g olivine (63%alk + 5%Si + 32%Fe) (Hauck et al., in prep)
(6) Ships of opportunity: Ballast water of ships has potential to dissolve 0.9 Pg olivine. Peter Köhler 10 October 2015 dissolution kinetics ship tracks dissolution (%) of 1µm particles based on NOAA data particle dissolution slow Southern Ocean: (Köhler etal., 2013) no ships to go
(1) Potential: Process changes carbonate system CO 2 removal potential 20% smaller (2) Dissolution kinetics: Only particles of 1µm sink slow enough for surface dissolution. (3) Chemistry: CO 2 removal dominated by alkalinization ( 90%) with add-on by silicate fertilization. (4) Marine Biology: Enhanced olivine dissolution is also ocean fertilization, leading to species shifts. (5) Iron: Iron fertilization (+50% CO 2 removal) is possible, but less feasible. (6) Ships of opportunity: Ballast water of commencial ships has potential to dissolve 0.9 Pg olivine. (7) Limitation: Local bottleneck might be the saturation concentration of silicic acid H 2 SiO 4. (8) ph: If distributed on land river ph might rise significantly. (9) Time: CO 2 removal is not permanent. (10) Size of problem: 3 Pg yr 1 of olivine to remove 1-2 Pg C yr 1 (coal production: 8 Pg yr 1 ). Peter Köhler 11 October 2015
References Peter Köhler 12 October 2015 Hartmann, J.; West, J.; Renforth, P.; Köhler, P.; De La Rocha, C.; Wolf-Gladrow, D.; Dürr, H. & Scheffran, J. 2013. Enhanced Chemical Weathering as a Geoengineering Strategy to Reduce Atmospheric Carbon Dioxide, a Nutrient Source and to Mitigate Ocean Acidification. Reviews of Geophysics, 51, 113-149. Köhler, P.; Abrams, J. F.; Völker, C.; Hauck, J. & Wolf-Gladrow, D. A. 2013. Geoengineering impact of open ocean dissolution of olivine on atmospheric CO 2, surface ocean ph and marine biology. Environmental Research Letters, 8, 014009. Köhler, P.; Hartmann, J. & Wolf-Gladrow, D. A. 2010. Geoengineering potential of artificially enhanced silicate weathering of olivine. Proceedings of the National Academy of Science, 107, 20228-20233.
The End Peter Köhler 13 October 2015
Open questions Peter Köhler 14 October 2015 Dissolution kinetics of olivine not yet clear, our theory needs support from experiments. Scavenging and ballast effect might effect how much iron is biological available.