Margaret Leinen

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Oceans a carbon sink or sinking ecosystems?
Margaret Leinen Chief Science Officer Climos
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• What is the role and status of the ocean as a
  carbon sink?
• How is increased CO2 affecting the ocean and its
  ecosystems?

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45 of annual carbon flux is processed by
phytoplankton
THE BIOLOGICAL PUMP

• Plankton grow, mature and dietaking 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 planktonthey form
  the base of the marine food chain.

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The biological pump efficiently transfers carbon
to the deep ocean
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Atmospheric CO2 Concentration
Year 2006 atmospheric CO2 concentration 381
ppm 35 above pre-industrial
CO2
1850
1870
1890
1910
1930
1950
1970
1990
2010
NOAA 2007 Canadell et al. 2007, PNAS
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Anthropogenic C Emissions Fossil Fuel
2006 Fossil Fuel 8.4 Pg C
2006-Total Anthrop. Emissions8.41.5 9.9 Pg
1990 - 1999 1.3 y-1 2000 - 2006 3.3 y-1
Raupach et al. 2007, PNAS Canadell et al 2007,
PNAS
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Trajectory of Global Fossil Fuel Emissions
SRES (2000) growth rates in y -1 for
2000-2010 A1B 2.42 A1FI 2.71 A1T
1.63 A2 2.13 B1 1.79 B2 1.61
Observed 2000-2006 3.3
Raupach et al. 2007, PNAS
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Drivers of Anthropogenic Emissions
1.5
1.5
1.5
World
1.4
1.4
1.4
1.3
1.3
1.3
1.2
1.2
1.2
1.1
1.1
1.1
Factor (relative to 1990)
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
Emissions
F (emissions)
P (population)
0.7
0.7
0.7
g G/P
0.6
0.6
0.6
h F/G
0.5
0.5
0.5
1980
1985
1990
1995
2000
2005
1980
1980
Raupach et al 2007, PNAS
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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 worlds economy has
  stopped decreasing (after 100 years of doing so).

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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
Land removes 30
Ocean removes 24
Canadell et al. 2007, PNAS
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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
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Perturbation of the Global Carbon Budget
(1959-2006)
Canadell et al. 2007, PNAS
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Source NCAR
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Time Dynamics of the Airborne Fraction
The observed trend in Airborne Fraction was
0.25 per year (p 0.89) from 1959-to 2006,
implying a decline in the efficiency of natural
sinks of 10
Distribution (fraction)
1960 1970 1980 1990 2000
time
Canadell et al. 2007, PNAS
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The Efficiency of Natural Sinks Land and Ocean
Fractions
Land
Ocean
Canadell et al. 2007, PNAS
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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.
• 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.

Credit N.Metzl, August 2000, oceanographic
cruise OISO-5
Le Quéré et al. 2007, Science
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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

• To
• Economic growth
• Carbon intensity
• Efficiency of natural sinks

2000 - 2006 1.9 ppm y-1
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
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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.

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• What is the role and status of the ocean as a
  carbon sink?
• How is increased CO2 affecting the ocean and its
  ecosystems?

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• CO2 H2O H2CO3
• H2CO3 can dissociate to
• Bicarbonate HCO3-
• Carbonate CO3-2
• At normal ocean pH, 90 of the carbon is in
  bicarbonate, 9 is in carbonate, 1 is in CO2

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Royal Society, 2005
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Royal Society, 2005
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Scientific American 2006, Doney, The Dangers of
Ocean Acidification
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• 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

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Leslie Sautter, Project Oceanica
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• Corals
• Also aragonite, the most soluble form for CaCO3

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• 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)

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• 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

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• 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

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• 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