Carbon Cycle
Introduction
Inez Fung
2nd NCAR-MSRI Summer Graduate Workshop on Carbon
Data Assimilation
NCAR July 9-13 2006
High-precision Atm
CO2: at MLO since
1958
• 180 ppmv Last
Glacial Maximum
• 280 ppmv in the
preindustrial
(~1800AD)
• 380 ppmv in 2005
Units
3 3C air
C air
14 2
2 18mb
6
C( kgC / m ) ( kgAir / m ) ( MWt / MWt )
MWt 12gm / mole; MWt 29gm / mole
Area dxdydz 5 10 ( m )
100PMassAtm dxdydz ( kgAir / m ) Area ~ 5 10 kgAir
g
12MassC( 300 ppmv )
X( moleC / moleAir )
MassAtm ( 300 x10 ) ( )29
~ 60
=
= =
= =
= =
=
12
1PgC 0.5 p
0 10 kg 6
pmv( mi
00PgC 600GtC
xed _entireAtm )
= =
Outstanding Questions
• Only half of the CO2
produced by human
activities is remaining in
the atmosphere
• Where are the sinks that
are absorbing over 40% of
the CO2 that we emit?
– Land or ocean?
– Eurasia/North America?
• Why does CO2 buildup
vary dramatically with
nearly uniform emissions?
• How will CO2 sinks
respond to climate
change?
Continuous Carbon Cycling
• Fluxes PgC/yr
• Inventory PgC
• Turnover time
=
Inventory/Flux
• Atm CO2 --> inventory
• Land: turnover time 101-102 yrs. Ocean: turnover time 102-103 yrs
• Difficult (time consuming and expensive) to measure changes in land
and ocean inventories. Focus on fluxes
Conservation of Carbon in Atm
{ {{
Atm _transport mixing
z 0
SourcesSinChem P
kr od
s
SC
( )t
C P=
+
+ +=
oa b bao a a( F FLandUs )eS )F ( F FF= + + +
bao ba a ao( F F
C C C
( F F
'
C ) )( ) +
= +
=
Separate out background (pre-industrial) from the
perturbation (last 200 years) carbon cycle:
Pre-industrial:
Conservation of Perturbation Carbon in Atm
{ {{
Atm _transport mixing
z 0
SourcesSinChem P
kr od
s
SC
( )t
C P=
+
+ +=
oa b bao a a( F FLandUs )eS )F ( F FF= + + +
In later lectures, the conservations equation may appear as:
b i 1 a iT ( t ) M [T ( t )]+ =
i 1 i( x ) ux G( )+ = +
Kalnay:
Nychka:
Conservation of Perturbation Carbon in Atm
{ {{
Atm _transport mixing
z 0
SourcesSinChem P
kr od
s
SC
( )t
C P=
+
+ +=
oa b bao a a( F FLandUs )eS )F ( F FF= + + +
Fossil Fuel Emission
>95% emission in
Northern Hemisphere
Atm CO2 Signature of Fossil Fuel Emission:
N-S gradient
Conservation of Perturbation Carbon in Atm
{ {{
Atm _transport mixing
z 0
SourcesSinChem P
kr od
s
SC
( )t
C P=
+
+ +=
oa b bao a a( F FLandUs )eS )F ( F FF= + + +
Terrestrial Carbon Cycle
• Growth, mortality, decay
• GPP: Gross Primary
Productivity (climate,
CO2, soil H2O, resource
limitation)
• Ra: Autotrophic
respiration (T, live
mass,…)
• Rh: Heterotrophic
respiration: Decay (T,
soil H2O,..)
• NPP=GPP-Ra
120 PgC/yr 60 60
1200 PgC
800 PgC
GPP Ra Rh
Deforestation
Tough to estimate
• deforested area
• Carbon inventory before
deforestation
• Fate of removed carbon
• Fate of litter and soil carbon
Tough to discriminate atm
CO2 signature
Veg Type(x,y)
annual
mean NPP(x,y)
NDVI-seasonal
August 2000
February 2001
Satellite
Greenness
index: NDVI
Seasonality
of NPP
Seasonality of
Respiration not
well-defined
Net flux not
well-defined at
every location
Impact on Atmospheric CO2
Photosynthesis
Respiration
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Jan Dec
From Atm
To Atm
CO
2 F
lux
• Seasonal asynchrony
between photosynthesis and
decomposition
net fluxes of CO2 to and
from atm
seasonal cycle of CO2 in
atm
• Annual imbalance carbon
source/sink
Atmospheric CO2 Signature of Ecosystem C
Exchange: Seasonal Cycle
Mauna Loa, HawaiiPt. Barrow, Alaska
6.5 ppmv 16 ppmv
Source:
NOAA/CMDL
• Amplitude of atmospheric CO2 seasonal cycle increases poleward:
telecoping of growing season and greater asynchroneity bet’ fluxes
• Growing season net flux ~15-20% of annual NPP
Conservation of Perturbation Carbon in Atm
{ {{
Atm _transport mixing
z 0
SourcesSinChem P
kr od
s
SC
( )t
C P=
+
+ +=
oa b bao a a( F FLandUs )eS )F ( F FF= + + +
Ocean C from the Atm’s Perspective:
DIC = CO2* + HCO3
- + CO3=
1-2 % 80-90%
CO2
DIC, NO3
depth
atm
remineralizatio
n
photosyn
100 Pg C/yr
{ {oa aoGasExchRate( m / s ) so lub ility(T )mol
atm _ssfc _ocn
e /
f
m3
c
C
CO2* pCOF k )2F (=1442443
Marine
Productivity
Is possible when
upwelling brings:
•Nutrients from below
to euphotic zone
•Cold water
Small Flux, small inventory
of organic C
But alters DIC(z)
-Global baseline (hydrography, transient tracers,nutrients, carbonate system)-Improved analytical techniques for inorganic carbonand alkalinity (±1-3 μmol/kg or 0.05 to 0.15%)-Certified Reference Materials-Data management, quality control, & public data access
JGOFS/WOCE global survey (1980s and 1990s)
OceanC : Mainly
Dissolved Inorganic
Carbon (DIC)
Biology and DIC:
•Depletion near sfc
•Enrichment at
Depth
Latitude N
Dep
th
Atlantic Pacific
Conveyor Belt Transport of
DIC:
•Southward in Atlantic
•Northward in Pacific
Ocn currents ~ cm/s
Time scale ~ 103 yr
Air-Sea Fluxes of CO2
{ {
ocn oa ao
sfc _ocn atm _sfcGasExchRate( m / s ) so lub ility(T )moleC / m3
F F F
k (CO2* pCO2 )
=
=1442443
SUMMARY
{ {z 0
SourcesSinksAtm _transport mixing
boa ao a ab
S
S
(C )
( FLandUse ( F F
C
))
t
FF F
+
=+ =
= + + +
FF: mainly NH, relatively aseasonal
LandUse: mainly source tropics, sink in mid-latitudes
Ocean: outgassing in equatorial oceans, absorption
at mid-hi latitudes (in summer. Not sure about winter)
Vegetation and soils: annual mean fluxes~0 locally,
fluxes have large diurnal (~100 ppmv) and seasonal
ranges (~30 ppmv)
Atm CO2 data for assimilation
Atm CO2 Observations
• In situ: tower, continuous
• Flask: 2m, twice weekly, ~102 locations
• >400m Tall Tower: 11, 30, 76, 122, 244
and 396 m; Continuous
• Aircraft data
• Very few obs over land (CO2 very
variable)
• Upcoming: satellite data, column, (106
locations twice weekly)
WLEF, Park Falls, Wisconsin
Mauna Loa, Hawaii
In-situ Atmospheric Observing Network
Discrete surfaceflasks (~weekly)
Continuoussurface (hourly)observatories
Tall towerscontinuous(hourly)
Aircraftprofiles(~weekly)
Global Distribution of CO2 in the lower
troposphere
• secular trend
• N-S gradient
• Seasonal cycle
• Interannual variations
CO2 Concentration in the Outer Damon Room, NCARMesa Lab, 2/7 – 2/9/06
CC
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Clim
ate
Wo
rkin
g G
rou
pBoard of Trustees
ReceptionNational Science
Board Breakfast
ASP Reviews
Surface Observatories
Where both
insitu
(hourly) and
flask
(biweekly)
data are
taken:
Diurnal and
weather
cycles on top
of seasonal
cycles
Seasonal CO2: Continental vs Oceanic Sites
•CO2 seasonal cycle attenuate, but still coherent, far away
from source/sink region
•Peak-trough amplitude of seasonal cycle ~ 30 ppmv
(~10%)
Diurnal CO2: Highly variable in boundary layer
10 11 12 13 14 15 16 17
345
355
365
375
385
395
405
340
350
360
370
0-396 m Column Integral
WLEF Tall Tower, Park Falls, WI
11 m 30 m 76 m122 m244 m396 m
(Peter Bakwin, CMDL, 2001)•Diurnal cycle of photosynthesis and respiration
> 60 ppmv (20%) diurnal cycle near surface
•Varying heights of the planetary boundary layer (varying mixing volumes)
Calm night:
stably stratified
boundary layer
Well-mixed
PBL
Vertical Profiles (free troposphere)
384
372
20062005 DATE
AircraftCampaigns
COBRA 2000
Surface Fluxes => Atmospheric CO2
Orbiting Carbon Observatory(Planned Dec 2008 launch)
• Estimatedaccuracy forsingle column~1.6 ppmv
• 1 x 1.5 kmIFOV
• 10 pixel wideswath
• 105 minute polarorbit
• 26º spacing inlongitudebetween swaths
• 16-day returntime
Multiple Time/Space Scales g
GCM CarbonCentury
Decade
Year
Day
Hour
TIM
E
Plot Tower Landscape Region Continent Globe
1-D
BGC
Tower
Flux
Aircraft Flux
Satellite GPP, NPP
Tower
Footprint
Orbiting
Carbon
Observatory
Atmospheric
Inversion
SPACE
GCM CarbonCentury
Decade
Year
Day
Hour
TIM
E
Plot Tower Landscape Region Continent Globe
1-D
BGC
Tower
Flux
Aircraft Flux
Satellite GPP, NPP
Tower
Footprint
Orbiting
Carbon
Observatory
Atmospheric
Inversion
SPACE