Ocean Acidification and the
Future Global Carbon Cycle
Jack Barth (barth@coas.oregonstate.edu)
College of Oceanic & Atmospheric Sciences
•Rising atmospheric CO2
•Ocean’s role in uptake of atmospheric CO2
•Resulting changes in ocean chemistry
•Possible outcomes for future oceans
•What can we can do to help improve the future?
for further info: “The Future of Ocean Biogeochemistry in a High
CO2 World,” Oceanography magazine (Dec. 2009)
http://www.tos.org/oceanography/issues/issue_archive/22_4.html
Rising Atmospheric CO2 was first discovered by
Dr. David Keeling in the mid 1900s.
Data from Keeling and Whorf, 2004
Atmospheric CO2 Record
Atmospheric CO2 levels are rising
everywhere in the world. This can easily
be seen even with the natural variability.
Northern
Hemisphere has
larger seasonal
variability than
southern hemisphere
Atmospheric CO2 was steady for at least 1,000 years
before the industrial revolution.
Antarctic Ice Core Record
“It is very likely that [man-made]
greenhouse gas increases caused most
of the average temperature increase
since the mid-20 century”
- Intergovernmental Panel on Climate
Change (IPCC) 4th Assessment
Report (2007)
2100
800
2050
550
400
CO2 concentration
15
10
5
200
0
-5
Temperature change (°C)
-10
450
400
350
300
0
250
200
Thousands of years BP (before present)
150
100
50
0
CO2 Concentration (ppmv)
Temperature change (°C)
20
issions
CO (GtC y
5
0
Recent Recent
emissions emissions
have been higher than the
worst of the IPCC projected scenarios
1850
1900
1950
2000
2050
10
8
7
50-year constant
growth rates
to 2050
2007
2006
B1
1.1%,
A1B 1.7%,
A2
1.8%
A1FI 2.4%
Observed
2000-2006
3.3%
2
Emissions
CO (GtC y
GigatonsC/year
) -1
9
Actual emissions: CDIAC
Actual emissions: EIA
450ppm stabilisation
650ppm stabilisation
A1FI
A1B
A1T
A2
B1
B2
2100
6
5
1990
1995
2000
Year
2005
2010
Carbon Inventories of Reservoirs that Naturally
Exchange Carbon on Time Scales of Decades to Centuries
Ocean Anth.
C=0.35%
Soil=2300 PgC
Plants=650 PgC
Atm.=775 PgC
Ocean
38,136 PgC
Preind.
Atm. C
=76%
Anth.
C=24%
• Oceans contain ~90% of carbon in this 4 component system
• anthropogenic component is difficult to detect
In the 1990s we conducted a global survey of CO2 in the
oceans to learn how much fossil fuel is stored in the ocean.
~72,000 sample locations
collected in the 1990s
DIC ± 2 µmol kg-1
TA ± 4 µmol kg-1
Penetration of human-caused CO2 into Ocean
•Present-day levels minus preindustrial (year 1800)
•Equivalent to about half of all
historical fossil fuel emissions
Sabine et al. (Science, 2004)
Rising atmospheric CO2 is changing the chemistry of the ocean
CO2 is an acid gas so the addition of 22 million tons of
carbon dioxide to the ocean every day is acidifying the
seawater…we call this process “ocean acidification”
CO2 + H2O
H2CO3
HCO32- + H+
pH
After Turley et al., 2005
CO3- + H+
Ocean Measurements of pCO2 and pH
Feely et al. (2009)
Ocean Acidification
CO2 + CO32- + H2O  2HCO3Saturation State =
W
Ca2+ + CO32-  CaCO3
calcium + carbonate
Photos courtesy Katie Fagan
 calcium
carbonate
phase
[Ca2+] [CO32-]
=
K*sp, phase
W > 1 = precipitation
W = 1 = equilibrium
W < 1 = dissolution
There appears to be a linear decrease in the calcification rate of
coral reef systems with decreasing carbonate ion concentrations in
Biosphere 2 Corals
Coral Calcification rate
mmol m-2 d-1
3X
Glacial 1870 2006 CO2 CO2
Time
200
150
2X
180
280 380 560 840
R2 = 0.843
200
CO2 level in
Atmosphere
(ppm)
100
100
Net
Calcification
50
0
150
450
400
350
300
250
200
Carbonate ion concentration (µmol kg-1)
-50
Low CO2
150
100
50
Net Dissolution
50
0
-50
High CO2
Langdon & Atkinson, (2005)
Predictions of Ocean Acidification and
the effects on coral reef calcification
Coral Reef
calcification
• 1765 Adequate
• 2000 Marginal
• 2100 Low
After Feely et al (in press) with Modeled Saturation Levels from Orr et al (2005)
Predictions of Ocean Acidification and
the effects on coral reef calcification
Coral Reef
calcification
• 1765 Adequate
• 2000 Marginal
• 2100 Low
Calcification
rates in the
tropics may
decrease by
30% over the
next century
After Feely et al (in press) with Modeled Saturation Levels from Orr et al (2005)
Coccolithophores
pCO2 280-380 ppmv
pCO2 780-850 ppmv
Calcification
decreased
- 9 to 18%
Emiliania huxleyi
- 45%
Gephyrocapsa oceanica
Manipulation of CO2 system by addition of HCl or NaOH
Riebesell et al.(2000); Zondervan et al.(2001)
The shells of living pteropods begin to dissolve
at elevated CO2 levels
Whole shell:
Clio pyramidata
Arag. rods exposed
Prismatic layer
(1 µm) peels back
Limacina helicina
Aperture (~7 µm):
advanced dissolution
(Orr et al., 2005)
Micrographs from Victoria Fabry, CSUSM
Normal shell: unexposed
to undersaturated water
C. pyramidata
ARCOD@ims.uaf.edu
Potential Effects on Open Ocean Food Webs
Coccolithophores
Copepods
Barrie Kovish
Pacific Salmon
Vicki Fabry
Pteropods
Pteropods make up 45% of the pink salmon diet
amphipods (likely also affected by OA) make up 32% of diet
What we know about the biological impacts of ocean
acidification ...and sensitivity to CO2/pH perturbation
Much of our present knowledge stems from
 abrupt CO2/pH perturbation experiments
 with single species/strains
 under short-term incubations
 with often extreme pH changes
Hence, we know little about
 responses of genetically diverse populations
 synergistic effects with other stress factors
 physiological and micro-evolutionary adaptations
 species replacements
 community to ecosystem responses
 impacts on global climate change
Where will the future take us?
CO2 levels have been higher in the past,
But with every major rise there have been mass extinctions
CENOZOIC
MESOZOIC
PALEOZOIC
PRECAMBRIAN
Number of
Genera
65
Cretaceous/
Tertiary
200
Triassic/
Jurassic
251
Permian/
Triassic
360
Late
Devonian
444
Ordovician/
Silurian
Age (Ma)
Era
Coral Reef Gap
From Signor (1990)
How will these changes affect the global
carbon cycle in the future?
Carbon Cycle Change
Climate Feedback
direction
CO32- decrease
Less efficient uptake
positive
Calcification decrease
lower natural CO2 production
negative
CaCO3 dissolution-sed.
higher CO32- increasing uptake
negative
CaCO3 dissolution-water higher CO32-/lower org. transport Neg./pos.
Increasing SST
Convert ocean HCO3- to CO2
positive
Increased stratification Reduced mixing and transport
positive
Increased stratification Lower productivity and uptake
positive
Increased dust input
Increased productivity-N fixers
negative
Ecosystem structure
Lower or higher productivity
Pos./neg.
Future
Present
Ocean
Ocean
Food
Food
Web
Web
– Simpler,
– Complex
more
ecosystem
primitive
interactions
ecosystem based
based on
on aa low
highCO
CO
ocean
2 2ocean
Provided by James Barry MBARI
Primary Producers
Simplified Food Web,
Increased Microbial Dominance
Seafloor community
Microbial Remineralization
Acidic waters
brought near the
coast by coastal
upwelling
Possible changes to:
• species composition &
abundances
• food webs
• biogeochemical cycles
Feely et al. (2008)
Dissolved oxygen
and pCO2
measured off
Oregon
Aug & Sep
hypoxic
Courtesy of MI_LOCO
(Barth, Adams, Chan)
High pCO2/low pH waters may
affect oyster hatcheries
Whiskey Creek
Hatchery,
Netarts Bay, OR
“Spat” on shell, newly
metamorphosed juvenile oysters,
after their larval stage.
“Spat” raised in
hatchery, not on shell.
www.netartsbaytoday.com
Courtesy of George
Waldbusser
(COAS/OSU)
How a bivalve shell is formed
From McConnaughey & Gillikin 2008
Two sources of Shell
Carbonate
Seawater HCO3Respired CO2
Two components of
shell growth, organic
and inorganic.
Internal shell
surface is used to
buffer during
exposure or stress.
Calcification in bivalves is an Internal process,
Dissolution is primarily External*
Courtesy of George
Waldbusser
(COAS/OSU)
Conclusions
1. Atmospheric CO2 is growing at an exponential rate
2. The ocean has provided a great service to society by helping
to slow the rate of atmospheric increase.
3. The addition of >200 billion metric tonnes of carbon to the
ocean over the last 100 years has lowered ocean pH by 0.1
unit.
4. By the end of this century pH may drop by another 0.3 units
and will likely have dramatic consequences on the ocean
ecosystems.
5. The rate of CO2 growth may impact the ability of the ocean
to adapt to climate change…slowing the rate of growth could
determine the structure of the future oceans.
for further info: “The Future of Ocean Biogeochemistry in a High CO2
World,” Oceanography magazine (Dec. 2009)
http://www.tos.org/oceanography/issues/issue_archive/22_4.html