Carbon Cycle1. Introduction

Inez FungUC Berkeley

MSRI-NCAR Summer Graduate Workshop on Carbon Data Assimilation

MSRI July 17-28 2006

Continuous Carbon Cycling• Fluxes PgC/yr

• Inventory PgC

• Turnover time= Inventory/Flux

Mauna Loa Observatory & C.D. Keeling

• 180 ppmv Last Glacial Maximum

• 280 ppmv in the preindustrial (~1800AD)

• 380 ppmv in 2005

High-precision AtmCO2: at MLO since 1958

Atm CO2 Observations in lower troposphere

WLEF, Park Falls, Wisconsin

Mauna Loa, Hawaii

• In situ: tower, continuous • Flask: 2m, twice weekly• >400m Tall Tower: 11, 30, 76, 122,

244 and 396 m; Continuous

Global Distribution of CO2

• secular trend• N-S gradient• Seasonal cycle• Interannual variations

Globally averaged CO2

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 )100P

MassAtm dxdydz ( kgAir / m ) Area ~ 5 10 kgAirg

12MassC( 300 ppmv )

X(moleC / moleAir )

MassAtm ( 300x10 ) ( )29~ 60

ρ

ρ

−

= × ×

= =

= = ×

= = × ×

= × ×

∫

∫

12

1PgC 0.5 p0 10 kg 6

pmv(mi00PgC 600GtCxed _entireAtm )→

× = =

Atm CO2 increase ~50% FF emission

0

1

2

3

4

5

6

7

8

1980 1985 1990 1995 2000

Fossil Fuel emission

Atm increase

Land and Ocean

PgC/yr

Conservation of Carbon in Atm

Atm _transport mixingz 0

SourcesSinChem P

kr od

s

SC ( )t

C P=+

∂+ +

∂ℑ =

oa b bao a a( F FLandUs )eS )F ( F FF − −= + + +

bao ba a ao( F F

C C C

( F F

'

C ) )( ) − + −

= +

ℑ =

Fossil Fuel Emission

>95% emission in Northern Hemisphere

Atm CO2 Signature of Fossil Fuel Emission: N-S gradient

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

Tough to estimate • deforested area• Carbon inventory before

deforestation• Fate of removed carbon• Fate of litter and soil carbonTough to discriminate atm CO2

signature

Deforestation

Veg Type(x,y) annual

mean NPP(x,y)

NDVI-seasonal

August 2000

February 2001

Satellite Greenness index: NDVI

Seasonality of NPP

Seasonality of Rh 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

2Fl

ux

• 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, Hawaii Pt. 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

Ocean C from the Atm’s Perspective:

DIC = CO2* + HCO3

- + CO3=

1-2 % 80-90%

CO2

DIC, NO3depth

atm

remineralization

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 ( β− = × − ×

Is possible when upwelling brings:

•Nutrients from below to euphotic zone•Cold water

Small Flux, small inventory of organic CBut alters DIC(z)

Marine Productivity

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 PacificOcn currents ~ cm/sTime 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 Fk (CO2* pCO2 )

∆β

= −

= × − ×

Atm CO2 Signature of Air-sea Flux: Tough

• Ocean circulation redistributes C in ocean

• Expect elevated CO2 at equator, lower CO2 at high latitudes

• Difficult to separate from FF and other signatures

0.8 ppmv

0

-0.80 80N80S

Atlantic transect

Pacific transect

Modeled atm CO2

SUMMARY

z 0SourcesSinksAtm _transport mixing

boa ao a ab

S

S

(C )

( FLandUse ( F F

C

))

t

FF F+

=ℑ

− −

∂+ =

∂

= + + +

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)