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The Effect of Increasing COThe Effect of Increasing CO22 on on the World’s Oceansthe World’s Oceans
Mark CarsonUW 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• Various negative impacts on ocean biology
(and thus our economies) are likely
• Well, we all know quite a bit about it Well, we all know quite a bit about it already, but in summary:already, but in summary:
Plants (including phytoplankton and some bacteria) use it:Plants (including phytoplankton and some bacteria) use it: COCO22 + H + H22O +O + sunlight CHsunlight CH22O + OO + O22
Animals (including many bacteria) respire it:Animals (including many bacteria) respire it:
OO22 + CH + CH22O COO CO22 + H + H22O + energyO + energy
And we (plus Nature to a degree) produce it through And we (plus Nature to a degree) produce it through burning organic matter:burning organic matter:
nCnCyyHH2y+22y+2 + mO + mO22 (+ xN (+ xN22) wCO) wCO22 + vH + vH22O (+ rCO + sNOO (+ rCO + sNOqq) + energy!) + energy!
What is Carbon Dioxide?
Photo by Mark Carson
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, 2006Photo by Mark Carson
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, 2005Photo by Mark Carson
Graphics sources: “Carbon Dioxide” Wikipedia article (top); GEMS GHG Flux Inversion (middle and bottom)
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
Ocean color (Chl) Apr 09
Source: AQUA MODIS Monthly Chlorophyll concentration, level 3, April 2009; oceancolor.gsfc.nasa.gov
Pteropod, or sea butterfly,Clio Pyramidata,Up to 2 cm size
The biological players
Graphics: pteropod: www.ipsl.jussieu.fr/~jomceCoccolithophorid: www.biol.tsukuba.ac.jp/~ikawa/shiraiwaHPForaminifera: O. R. Anderson, accessed from the Micro Scope website
Foraminifera,Globigerinoides species,Usu. Less than 1 mm
Coccolithophorid, E. Huxleyi,About 6 μm in size
Marine Carbon Chemistry
• When you add CO2 to seawater,
CO2 + H2O H2CO3
• H2CO3 (carbonic acid) dissociates as an acid in solution:
H2CO3 HCO3- + H+ CO3
2- + 2H+
[CO2 + H2CO3 sometimes written CO2(aq)]
Bicarbonate ion
Carbonate ion
Hydrogen (hydronium) ions pH
Source: (upper left) Feely et al. 2006, science brief; (right bottom) After Doney et al. 2009
Seawater time series from Aloha station, Hawaii:hahana.soest.hawaii.edu
(CO2 data from Mauna Loa, Hawaii)
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
Aragonite
Calcite
Graphic sources: Wikipedia
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.
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
Shell malformation
Graphics: NOAA OA Fact Sheet, 2008 (top); J. Cubillos (from www.aad.gov.au; bottom)
(b) Pteropod shell formation in high CO2
Coccolithophorid shell formation in high CO2 conditions (right)
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, 20082: Wilkinson, 2004; 3: Hoegh-Guldberg, 2005
The power of life
• Organisms can take acquired energy and apply it to things like binding Ca2+ and CO3
2- 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
Various responses to increased CO2
• Note that the few species just benefit from increased CO2 in this study
Source: Doney et al. 2009
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
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
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
“… 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