Ocean Acidification and the Future Global Carbon Cycle

1
Ocean Acidification and the Future Global Carbon
Cycle

• Intro to rising atmospheric CO2
• Oceans 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?

2
Rising Atmospheric CO2 was first discovered by
Dr. David Keeling in the mid 1900s.
Data from Keeling and Whorf, 2004
3
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
4
Atmospheric CO2 was steady for at least 1,000
years before the industrial revolution.
5
2100
800
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 - IPCC 4th
Assessment Report
2050
550
400
CO2 concentration
200
Temperature change (C)
CO2 Concentration (ppmv)
Temperature change (C)
0
Thousands of years BP (before present)
6
Recent emissions have been higher than the worst
of the IPCC projected scenarios
50-year constant growth rates to 2050 B1
1.1, A1B 1.7, A2 1.8 A1FI 2.4
Observed 2000-2006 3.3
7
Carbon Inventories of Reservoirs that Naturally
Exchange Carbon on Time Scales of Decades to
Centuries
Ocean Anth. C0.35
Soil2300 PgC
Preind. Atm. C 76
Plants650 PgC
Atm.775 PgC
Anth. C24
Ocean 38,136 PgC

• Oceans contain 90 of carbon in this 4 component
  system
• anthropogenic component is difficult to detect

8
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
9
36
43
29
to -
13-23
55-26
Sabine and Feely, 2005
First 180 years the ocean absorbed 44 of
emissions
Last 20 years the ocean absorbed 36 of emissions
10
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 seawaterwe call this process
ocean acidification
CO2 H2O H2CO3 HCO32- H CO3-
H
pH
After Turley et al., 2005
11
Ocean Acidification
Saturation State
W gt 1
precipitation

calcium
carbonate
calcium carbonate
W 1
equilibrium
W lt 1
dissolution
 
Photos courtesy Katie Fagan
12
There appears to be a linear decrease in the
calcification rate of coral reef systems with
decreasing carbonate ion concentrations in
Biosphere 2 Corals
1870
2006
Glacial
Time
560
280
380
180
840
R2 0.843
Net Calcification
Carbonate ion concentration (µmol kg-1)
Net Dissolution
Low CO2
High CO2
Langdon Atkinson, (2005)
13
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)
14
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)
15
Known Locations of Deep-sea Corals
Data may reflect fishing or research effort
rather than density of coral

• Alaska - survey (RACE) observer (NORPAC)
  databases
• West Coast NMFS bottom trawl surveys observer
  programs
• Gulf and Southeastern US - literature citations
  fishery management council database
• Northeast - historical records NMFS bottom trawl
  surveys observer logbooks

16
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)
17
The shells of living pteropods begin to dissolve
at elevated CO2 levels
Limacina helicina
C. pyramidata
18
Potential Effects on Open Ocean Food Webs
Coccolithophores
ARCOD_at_ims.uaf.edu
Copepods
Barrie Kovish
Pacific Salmon
Vicki Fabry
Pteropods
19
Pteropods make up 45 of the pink salmon diet
amphipods (likely also affected by OA) make up
32 of diet
20
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

21
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
Age (Ma)
65
200
251
360
444
Cretaceous/ Tertiary
Triassic/ Jurassic
Permian/ Triassic
Late Devonian
Ordovician/ Silurian
Era
From Signor (1990)
22
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.
23
Present Ocean Food Web Complex ecosystem
interactions based on a low CO2 ocean
Future Ocean Food Web Simpler, more primitive
ecosystem based on a high CO2 ocean
Primary Producers
Zooplankton food web
Upper Trophic levels
Sinking Organic Debris
Provided by James Barry MBARI
Simplified Food Web, Increased Microbial Dominance
Microbial Remineralization
Seafloor community
24
What can we do to help?

• Buy green power
• Use compact florescent bulbs
• Turn electronics off when not in use

1. Conserve Resources
If every household in America changed 5
incandescent light bulbs to compact florescent
bulbs it would be the equivalent of taking a
million cars off the road
Electricity Generation 40
Transportation 32
25
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 gt200 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 changeslowing the
   rate of growth could determine the structure of
   the future oceans.

26
What will future generations say about the era we
are currently living in and the choices we made
that affected the world as we know it?
27
After Broecker 1991