Oceans: a carbon sink or
sinking ecosystems?
Margaret Leinen
Chief Science Officer
Climos
1
• What is the role and status of the
ocean as a carbon sink?
• How is increased CO2 affecting the
ocean and its ecosystems?
45% of annual carbon flux is processed by
phytoplankton
THE BIOLOGICAL PUMP
•Plankton grow, mature and
die—taking carbon with
them to the deep ocean
•They have a larger effect
on climate than any single
other process or group of
organisms.
•Of the ~750 billion tons of
CO2 that turn over
annually, plankton process
45%
•99% of marine life relies on
plankton—they form the
base of the marine food
chain.
3
The biological pump efficiently transfers
carbon to the deep ocean
4
Fossil Fuel Emiss
6
5
4
Year 2006
atmospheric CO2
concentration:
381 ppm
35% above pre-industrial
Atmoapheric [CO2] (ppmv)
Atmospheric CO2 Concentration
3
2
1
0
4001850
380
1890
1910
1930
1950
1970
1990
2010
[CO2]
[CO2]
360
340
320
2 ppm/year
300
280
1850
0.81850
Temperature (deg C)
1870
0.6
1870
1870
1890
1890
1910
1910
1930
1930
1950
1950
1970
1970
1990
1990
2010
2010
Temperature
0.2 C/decade
y-1
1970 – 1979: 1.3 ppm
1980 – 1989: 1.6 ppm y1
1990 – 1999: 1.5 ppm y-1
0.4
0.2
0
-0.2
-0.4
-0.6
1850
2000 - 2006: 1.9 ppm y-1
1870
NOAA 2007; Canadell et al. 2007, PNAS
1890
1910
1930
1950
1970
1990
2010
Anthropogenic C Emissions: Fossil Fuel
2006 Fossil Fuel: 8.4 Pg C
Atmoapheric [CO2] (ppmv)
Fossil Fuel Emission (GtC/y)
[2006-Total Anthrop. Emissions:8.4+1.5 = 9.9 Pg]
9
Emissions
8
7
6
5
4
3
2
1
0
1850
4001850
380
360
340
320
1870
1870
1890
1890
1910
1910
1930
1930
1950
1950
1970
1970
1990
1990
2010
2010
[CO2]
1990 - 1999: 1.3% y-1
2000 - 2006: 3.3% y-1
300
Raupach et al. 2007, PNAS; Canadell et al 2007, PNAS
280
2 ppm/year
5
Recent
emissions
Trajectory
of
Global
Fossil
Fuel Emissions
0
1850
1900
1950
2000
2050
CO2 Emissions (GtC y-1)
10
9
8
7
Actual emissions: CDIAC
Actual emissions: EIA
450ppm stabilisation
650ppm stabilisation
A1FI
A1B
A1T
A2
B1
B2
SRES (2000)
growth rates in
% y -1 for
2000-2010:
2006
2005
A1B: 2.42
A1FI: 2.71
A1T: 1.63
A2: 2.13
B1: 1.79
B2: 1.61
Observed
6
2000-2006
3.3%
5
1990
2100
1995
2000
Raupach et al. 2007, PNAS
2005
2010
Drivers of Anthropogenic Emissions
1.5
Factor (relative to 1990)
1.4
1.5
World
1.4
1.3
1.3
1.2
1.2
1.1
1.1
1
1
0.9
0.9
FEmissions
(emissions)
PPopulation
(population)
gWealth
= G/P= per capita GDP
hCarbon
= F/Gintensity of GDP
0.8
0.7
0.6
0.5
1980
1985
1990
Raupach et al 2007, PNAS
1995
2000
0.8
0.7
0.6
0.5
2005
1980
Global Carbon Project conclusions:
• Since 2000:
– The growth of carbon emissions from fossil fuels has
tripled compared to the 1990s and is exceeding the
predictions of the highest IPCC emission scenarios
– Atmospheric CO2 has grown at 1.9 ppm per year
(compared to about 1.5 ppm during the previous 30 years)
– The carbon intensity of the world’s economy has stopped
decreasing (after 100 years of doing so).
Partition of Anthropogenic Carbon Emissions into Sinks
[2000-2006]
45% of all CO2 emissions accumulated in the atmosphere
Atmosphere
The Airborne Fraction
The fraction of the annual
anthropogenic emissions that
remains in the atmosphere
55% were removed by natural sinks
Ocean removes ~ 24%
Land removes ~ 30%
Canadell et al. 2007, PNAS
Factors that influence CO2 uptake from the
atmosphere:
• Land:
– CO2 fertilization effect, soil respiration, N
deposition fertilization, forest regrowth, woody
encroachment, …
• Oceans:
– CO2 solubility (temperature, salinity), ocean
currents, stratification, winds, biological activity,
acidification, …
Canadell et al. 2007; Gruber et al. 2004
CO2 flux (Pg CO2 y-1)
Source
Sink
Carbon flux (Pg C y-1)
Carbon intensity
(KgC/US$)
Perturbation of the Global Carbon Budget (1959-2006)
Time (y)
Canadell et al. 2007, PNAS
13
Source: NCAR
Distribution (fraction)
Time Dynamics of the Airborne Fraction
1960
1970
1980
1990
time
Canadell et al. 2007, PNAS
2000
The observed trend
in Airborne Fraction
was +0.25% per year
(p = 0.89) from 1959to 2006, implying a
decline in the
efficiency of natural
sinks of 10%
The Efficiency of Natural Sinks: Land and Ocean Fractions
Land
Ocean
Canadell et al. 2007, PNAS
Causes of the decrease in efficiency of the ocean sink
• Part of the decline is attributed to
up to a 30% decrease in the
efficiency of the Southern Ocean
sink over the last 20 years.
Credit: N.Metzl, August 2000, oceanographic cruise OISO-5
• This sink removes annually 0.7 Pg
of anthropogenic carbon.
• The decline is attributed to the
strengthening of the winds around
Antarctica which enhances
ventilation of natural carbon-rich
deep waters.
• The strengthening of the winds is
attributed to global warming and
the ozone hole.
Le Quéré et al. 2007, Science
Attribution of Recent Acceleration of Atmospheric CO2
1970 – 1979: 1.3 ppm y-1
1980 – 1989: 1.6 ppm y1
1990 – 1999: 1.5 ppm y-1
2000 - 2006: 1.9 ppm y-1
To:
• Economic growth
• Carbon intensity
• Efficiency of natural sinks
65% - Increased activity of the global economy
17% - Deterioration of the carbon intensity of the global economy
18% - Decreased efficiency of natural sinks
Canadell et al. 2007, PNAS
Conclusions about the ocean sink from the
Global Carbon Project:
• “The efficiency of natural sinks has decreased by
10% over the last 50 years (and will continue to do
so in the future), implying that the longer we wait to
reduce emissions, the larger the cuts needed to
stabilize atmospheric CO2.”
• “All of these changes characterize a carbon cycle
that is generating stronger climate forcing and
sooner than expected.”
• What is the role and status of the ocean as
a carbon sink?
• How is increased CO2 affecting the ocean
and its ecosystems?
• CO2 + H2O
H2CO3
• H2CO3 can dissociate to
– Bicarbonate
– Carbonate
HCO3CO3-2
• At normal ocean pH, 90% of the
carbon is in bicarbonate, 9% is in
carbonate, 1% is in CO2
Royal Society, 2005
Royal Society, 2005
Scientific American 2006, Doney, The Dangers of Ocean Acidification
23
• Organisms that create skeletal
material out of CaCO3 require high
CO3 concentrations in seawater to
precipitate the CaCO3
• CaCO3 can be in the crystal form of
aragonite or calcite - aragonite is
much more soluble
Leslie Sautter, Project Oceanica
• Corals
– Also
aragonite, the
most soluble
form for
CaCO3
• Calcification of coral is projected to
decrease by 10-30% under doubled
CO2 concentrations (Gattuso et al,
1999; Kleypas et al, 1999)
• This is supported by laboratory
studies under doubled CO2
atmosphere (Langdon et al, 2000)
• Several times in the past had higher
atmospheric CO2 concentrations
without impacts on calcifiers,
however
• The high rate of CO2 increase has
led to an out of equilibrium condition
that is reflected in the decreasing pH
• Global change impacts physical processes
that can lead to feedback reducing the
effectiveness of the oceanic carbon sink
• But they are, so far, affecting the physical
solubility of CO2, not its uptake by
biological processes that transport CO2 to
deep water
• The increasing CO2 has impacts,
however,especially on calcifying
organisms
• Even if we eliminate CO2 emissions
now, we will observe impacts on
calcification from the current
atmospheric CO2 concentrations
• The only way to avoid this is direct
removal of CO2 from the atmosphere
• This will be one of the most difficult
problems to tackle