Modeling Modes of Variability in Carbon Exchange Between High Latitude

Ecosystems and the Atmosphere

Dave McGuire (UAF), Joy Clein (UAF), and Qianlai Zhuang (MBL)

Map Courtesy of Cath Copass

Organization of Talk

• Why is understanding carbon exchange of high latitude ecosystems important?

• Progress in modeling:- seasonal-scale exchange- interannual-scale exchange- decadal-scale exchange- century-scale exchange

• Summary

Feedbacks of Terrestrial Ecosystemsto the Earth’s Climate System

Regional Climate Global Climate

Terrestrial Ecosystems

ImpactsWater and

energyexchange

Exchange ofradiatively

active gases(CO2 and

CH4)

Delivery of

freshwater to Arctic Ocean

Global Soil Carbon Storage

Low Peatland Estimate High Peatland Estimate Non-Peatland A 1500 Pg C 1500 Pg C

High Latitude Peatland Low B 200 Pg C

High Latitude Peatland High C 450 Pg C

TOTAL Global Soil Carbon Storage

1700 Pg C 1950 Pg C

High Latitude Soil Carbon

Storage

High Latitude Non-Peatland D 400 Pg C

High Latitude Non-Peatland E 350 Pg C

TOTAL High Latitude Soil Carbon Storage

(+200 Pg C B)

550 Pg C

(+450 Pg C B)

850 Pg C

Proportion of Global Soil Carbon Storage in High

Latitudes

32%

44%

A= Schlesinger et al. (1991) B = Gorham (1990) C = Gorham (1991) D = Schlesinger et al. (1977) E = Post et al. (1985)

Strategy to Evaluate Seasonal Exchange of Carbon Simulated by Terrestrial Biosphere Models

Terrestrial models underestimate winter CO2 concentrations and drawdown CO2 too early in the spring (from Dargaville et al., 2002)

Seasonal Variability

• Winter Exchange- Does underestimate of atmospheric CO2 concentrations

in winter indicate that terrestrial ecosystem models should do a better job in representing controls over winter decomposition?

• Exchange at transition from winter to summer- Does early drawdown of atmospheric CO2 at the winter to summer transition indicate that terrestrial ecosystem should do a better job in representing consideration the effects of spring thaw on carbon exchange?

ALT (Obs.)

CO

2 [ppm]

-10

0

10MBC (Obs.) KTL (Obs.)

BRW (Obs.)

-10

0

10STM (Obs.)

F A J A O D J M M

CBA (Obs.)

F A J A O D J M M

SHM (Obs.)

F A J A O D J M M

-10

0

10 observedbaselinesnowpack

TEM

(from McGuire et al., 2000)

Effects of Snowpack on NMSDof High Latitude Stations(Wilcoxin Signed Rank Test)

CASAP = 0.0225

Base Snow

NMSD

0

2

4

6

8

10

12

AlertMould BayKotlney IslandBarrowStation MCold BayShemya

CenturyP = 0.0225

Base Snow0

10

20

30

40

50

60

TEMP = 0.0225

Base Snow0

5

10

15

20

25

30

35

40

(from McGuire et al., 2000)

(Running et al., EOS)

Coupling STM to TEM

Soil

Temperatures

at

Different

Depths

Upper Boundary Conditions

Heat Balance Surface

Snow Cover

Mosses

Frozen Ground

Thawed Ground

Frozen Ground

Lower Boundary Conditions

Heat Conduction

Heat Conduction

Heat Conduction

Moving phase plane

Moving phase plane

Lower Boundary

H(t)

Soil Thermal Model

H(t) Organic Soil

Mineral Soil

Output

Prescribed Temperature

Prescribed Temperature

Snow DepthMoss Depth

Organic Soil DepthMineral Soil Depth

Vegetation type;Snow pack; Soil moistureSoil temperature

TEM STM

Mean Net Carbon Exchange during the 1980s (Zhuang et al., 2003)

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

Barrow (BRW)Mould Bay (MBC) Station M (STM)

Niwot Ridge (NWR)Cape Meares (CMO)

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

ObservationControlSoil ThermalEffects

J F M A M J J A S O N D J F M A M J-6-5-4-3-2-1012345

J F M A M J J A S O N D J F M A M J

CO

2 [ppmv]

-6-5-4-3-2-1012345

J F M A M J J A S O N D J F M A M J

Key Biscayne (KEY) Mauna Loa (MLO) Kumukahi (KUM)

Ascension IS (ASC)Guam (GMI)Virgin Islands (AVI)

Samor (SMO) Palmer Stn (PSA) South Pole (SPO)

Cold Bay (CBA)

Month

Comparison of Observed and Simulated CO2 at Monitoring Stations

(from Zhuang et al., 2003)

Inter-annual Variability

• Climate- To what extent does variability in temperature, precipitation, and radiation influence inter-annual variability in carbon exchange?

• Disturbance- To what extent does variability in climate vs. disturbance

influence inter-annual variability in carbon exchange?

(Positive Values Indicate Carbon Release, Negative Values Indicate Carbon Storage)

Applicationof STM-TEMparameterizedfor black spruceat Taiga LTER tosimulate the Cfluxes of theNSA-OBSBOREAS site.

Field-basedestimates arebased on eddycovariancemeasurements.

Zhuang et al. 2002.

(from McGuire et al., in preparation)

CO2

Concentration

Climate(Temperature,Precipitation)

STM-TEMCarbon Pools

NPP RH

NCE

Fire Emissions

Fire regime(Severity,History)

Alaska and Canada CFLUXSTM-TEM runs July 2002

-20

-10

0

10

20

30

1960 1965 1970 1975 1980 1985 1990 1995

g C m

-2 yr

-1

CO2

CO2 + Climate

CO2 + Climate + Fire Disturbance

Uptake

Release

GAC 7/29/02 Rates weighted by area

Stations used to constrain atmospheric inversions of high latitudes

1978 1980 1982 1984 1986 1988 1990 1992 1994

Net Flux Anomaly (Pg C y

-1)

-0.50

-0.25

0.00

0.25

0.50

Alaska and Canada Carbon Flux Variability from an Atmospheric Inversion - R. Dargaville

Alaska and Canada Carbon Flux Variability from TEM

-0.50

-0.25

0.00

0.25

0.50

1978 1980 1982 1984 1986 1988 1990 1992 1994

Net Flux Anomaly (Pg C yr

-1)

Comparisonof process-basedand atmospheric approaches for Alaska-Canadaafter consideration of fire by theprocess-basedapproach

(from McGuire et al., In preparation)

Decadal Variability

• ClimateTo what extent do changes in the start and length of the growing season influence decadal changes in carbon storage? (Zhuang et al., 2003)

• DisturbanceCan responses of carbon exchange to changes in disturbance regime negate carbon storage that might be gained from longer growing seasons? (McGuire et al., in press).

Courtesy of K. McDonald

Biomass of Northern Hemisphere Ecosystemshas been Changing in Recent Decades

From Myneni et al. (2001)

(Fire in Canada became more frequent after 1970)

Cumulative Changes in Carbon Stocks for Canada from 1950-1995

-400

-200

0

200

400

600

800

1000

1960 1965 1970 1975 1980 1985 1990 1995

Tg C

CO2

CO2 + Climate

CO2 + Climate + Fire Disturbance

(from McGuire et al., in press)

Century-Scale Variability

• Will changes in vegetation distribution dominate?(McGuire and Hobbie, 1997)

• Will directional changes in disturbance regimes dominate?(Kurz and Apps, 1999; McGuire et al., in press)

• How sensitive is the response of carbon storage to how fast carbon cycles through soils? (Clein et al., 2000)

2010 2040 2070 2100

GEM

-1000-500

0500

10001500200025003000

TEMfast soil C

1920 1960 2000

-1000

-500

0

500

1000

1500

2000

2500

3000

ecosystem C soil C vegetation C

TEMreference

Change in Carbon Stocks (g C m

-2)

-1000-500

0500

10001500200025003000

Historical Projected

Cumulative Changes in Carbon Stocksfor the Toolik Lake Grid Cell

Soil carbon storage depends on the dynamics of carbon and nitrogen transformations in soils. From Clein et al. (2000)

1985-1994

2085-2094

TEM, reference TEM, fast soil C

Different representations of soil carbon transformations have different impacts on century-scale responses of carbon storage.

(from Clein et al., 2000)

Summary• Seasonal variation improved by representing insulating effects of snowpack on winter decomposition and representing freeze-thaw processes.

• Inter-annual responses to climate not well understood at large scales. At local scales responses depend on soil moisture. Need to more accurately represent hydrologic variability across the landscape.

• It is not clear whether improvement of decadal responses requires improved information on winter precipitation or requires improved snowmelt algorithms in models.

• Century-scale responses may be improved through better understanding of carbon and nitrogen transformations in soils.

• Disturbance can have strong effects on carbon storage at all time scales.