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The Effect of Increasing CO 2 on the World’s Oceans

The Effect of Increasing CO 2 on the World’s Oceans. Mark Carson UW School of Oceanography. Essential take-home messages. Ocean acidification is a separate issue from anthropogenic global warming The chemistry involved is well understood Confounded by unknown bio-feedbacks

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The Effect of Increasing CO 2 on the World’s Oceans

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  1. The Effect of Increasing CO2 on the World’s Oceans Mark Carson UW School of Oceanography

  2. Essential take-home messages • Ocean acidification is a separate issue from anthropogenic global warming • The chemistry involved is well understood • Confounded by unknown bio-feedbacks • Various negative impacts on ocean biology (and thus our economies) are likely

  3. What is Carbon Dioxide? • Well, we all know quite a bit about it already, but in summary: Plants (including phytoplankton and some bacteria) use it: CO2 + H2O +sunlight CH2O + O2 Animals (including many bacteria) respire it: O2 + CH2O CO2 + H2O + energy And we (plus Nature to a degree) produce it through burning organic matter: nCyH2y+2 + mO2 (+ xN2) wCO2 + vH2O (+ rCO + sNOq) + energy! Photo by Mark Carson

  4. Fossil Fuel CO2 • 100s of millions of years in the making of fossil fuel reservoirs • Out of perhaps 6500 Gt (billion tons) of recoverable fossil fuel C, we have consumed ~ 220 Gt C in 200 yrs 1,2 • Coal is the fastest growing fossil fuel; reserves depleted in less than 200 yrs at current rate 3 1 Pilson, 1998; 2 Sabine et al. 2004; 3 IEA, 2006 Photo by Mark Carson

  5. CO2 Residence Time • Residence time is some substance stays within some reservoir. • There is some uncertainty regarding the residence time in the atmosphere • One recent estimate suggests that 17-33% of anthropogenic CO2 will remain in the atmosphere after a 1000 yrs1. • A lower limit puts the residence time at over 100 yrs, though this is unlikely. 1: Archer, JGR, 2005 Photo by Mark Carson

  6. Graphics sources: “Carbon Dioxide” Wikipedia article (top); GEMS GHG Flux Inversion (middle and bottom)

  7. A Helpful Ocean • The oceans have absorbed between 25 – 50% of the anthropogenic CO2 emitted during the Industrial Era1,2 • Increases surface CO2 and deep ocean CO2 via sinking of particulate organic matter (POM) • Offsets the global warming effect by reducing atmospheric CO2 concentrations 1: Sabine and Feely, 2007; 2: NOAA Ocean Acidification Fact Sheet, May 2008

  8. Ocean color (Chl) Apr 09 Source: AQUA MODIS Monthly Chlorophyll concentration, level 3, April 2009; oceancolor.gsfc.nasa.gov

  9. The global carbon cycle PCC slide no. 040 Source: Sabine et al 2004

  10. The “biological carbon pump” Graphic: Sunda, Nature, 2010

  11. The biological players Pteropod, or sea butterfly, Clio Pyramidata, Up to 2 cm size Coccolithophorid, E. Huxleyi, About 6 μm in size Graphics:pteropod: www.ipsl.jussieu.fr/~jomce Coccolithophorid: www.biol.tsukuba.ac.jp/~ikawa/shiraiwaHP Foraminifera: O. R. Anderson, accessed from the Micro Scope website Foraminifera, Globigerinoides species, Usu. Less than 1 mm

  12. Marine Carbon Chemistry • When you add CO2 to seawater, CO2 + H2O H2CO3 • H2CO3 (carbonic acid) dissociates as an acid in solution: H2CO3 HCO3- + H+ CO32- + 2H+ [CO2 + H2CO3 sometimes written CO2(aq)] Carbonate ion Bicarbonate ion Hydrogen (hydronium) ions pH

  13. (CO2 data from Mauna Loa, Hawaii) Seawater time series from Aloha station, Hawaii: hahana.soest.hawaii.edu Source: (upper left) Feely et al. 2006, science brief; (right bottom) After Doney et al. 2009

  14. Carbonate Chemistry Source: Raven et al 2005

  15. Calcium Carbonate Ca2+ + CO32- CaCO3 • Two major crystal forms: calcite and aragonite • Aragonite is more soluble • Forams and coccolithophores form tests of calcite • Pteropods and coral reefs form aragonite Calcite Aragonite Graphic sources: Wikipedia

  16. Saturation • A solution is saturated with a substance when additional amounts don’t dissolve, and normally the substance can precipitate out. • The surface oceans are supersaturated with respect to calcium carbonate, although it doesn’t precipitate inorganically at these levels.

  17. Aragonite Saturation • Saturated = 1; supersaturated > 1; undersaturated < 1 • Tropical waters have higher supersaturation than the polar waters • Heading into the late 21st century, polar waters will start to approach undersaturation with respect to aragonite Source: Feely, et al., Oceanography, Dec 2009

  18. Shell malformation (b) Pteropod shell formation in high CO2 Coccolithophorid shell formation in high CO2 conditions (right) Graphics: NOAA OA Fact Sheet, 2008 (top); J. Cubillos (from www.aad.gov.au; bottom)

  19. Coral reefs • Corals may not be able to grow and maintain reefs after 840 ppm CO2 is reached, Fig. 11 • Corals also will suffer if ocean temperatures increase due to GHG • Already, due to non-climate-impact human activity, over a quarter of reefs have collapsed or are in danger2 • ~100 million people rely on coral reefs in some way3 1: NOAA OA Fact Sheet, 2008 2: Wilkinson, 2004; 3: Hoegh-Guldberg, 2005

  20. The power of life • Organisms can take acquired energy and apply it to things like binding Ca2+ and CO32- together • Some plankton will fail in higher pH waters, some will survive. Some may thrive. • The Cliffs of Dover were formed by some species of coccolithophorids during the Cretaceous period, a period of very high CO2 concentrations Graphics source: Wikipedia

  21. Various responses to increased CO2 • Note that the few species just benefit from increased CO2 in this study Source: Doney et al. 2009

  22. Problems • The ability for plankton to acclimate quickly is uncertain • Seems likely that some species (like pteropods) may decline to some degree • Any decline in plankton or reefs will have consequences for the food webs • All organisms will have to “put more energy” into calcifying due to the carbonate chemistry issues presented here

  23. Impacts • Reduction of coral reef building and healthy calcareous shell formation in plankton • Impacts on larval forms of fish and shellfish • U.S. spends about $60 million on fish and seafood per year (3rd largest consumer in world) • U.S. fish stocks estimated at over $250 million Source: NOAA Ocean Acidification Fact Sheet, May 2008

  24. Reduced oceanic carbon sink? • Increased CO2 in the oceans will reduce the ocean uptake of CO2 • Limiting iron-utilization by diatoms et al.1 • Making calcifiers use HCO3- and release CO2 back into the water2 • Population declines in plankton / reefs due to acidification3 • Ocean warming due to GHG effect; warmer liquids can’t contain as much dissolved gas • The strength of these feedbacks is uncertain though; other possible theories include a strengthening of the oceanic carbon sink4 Sources: 1: Shi et al. 2010; 2: WBGU report, Jan. 2006; 3: NOAA OA Fact Sheet, 2008; 4: e.g., Engel et al. 2004

  25. “… human beings are now carrying out a large scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.” - Revelle and Suess, 1957 Source: Pilson, 1998

  26. Thanks! Source: (left) www.aad.gov.au/default.asp?casid=37046; (right) R. Feely, NOAA / PMEL

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