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

The global carbon cycle

Source: Sabine et al 2004PCC slide no. 040

The “biological carbon pump”

Graphic: Sunda, Nature, 2010

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)

Carbonate Chemistry

Source: Raven et al 2005

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

Thanks!

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