the observed responses of ecosystem co2 exchange to climate variation from diurnal to annual time...
TRANSCRIPT
The observed responses of ecosystem CO2 The observed responses of ecosystem CO2 exchange to climate variation from diurnal exchange to climate variation from diurnal
to annual time scale in the northern to annual time scale in the northern America.America.
C. Yi, K.J. Davis, The Penn State University
P.S. Bakwin, NOAA/CMDL
T. Zhou, Beijing Normal University
D.D. Baldocchi and colleagues, UC Berkeley
S. Wofsy and colleagues, Harvard University
Interannualvariabilityin the rate ofaccumulationof atmosphericCO2
IssuesIssues
• What climatic factors control the What climatic factors control the interannual variability in NEE?interannual variability in NEE?
Part I: Climate variables and NEE at various time scales
(NB, WB, WL, HF)
Respiration and temperature
Correlation between nighttime tower flux and air temperature is very high on daily, monthly and seasonal time scales.
Correlation breaks down on interannual scales.
Respiration and temperature
Northern OBS tower (NB)
Manitoba, Canada
Wofsy, Munger et al.
Boreal black spruce forest
Respiration and temperature
WLEF TV tower (WL)
Northern Wisconsin, USA
Davis, Bakwin et al.
Mixed forest/wetland mosaic
Respiration and temperature
Harvard Forest (HF)
Massachusetts, USA
Wofsy, Munger et al.
Deciduous forest
Respiration and temperature
Walker Branch tower (WB)
Baldocchi, Wilson et al.
Tennessee, USA
Deciduous forest
Why does the temperature-Why does the temperature-respiration relationship break respiration relationship break
down on annual time scales?down on annual time scales?
Hypotheses:
• Annual respiration is proportional to annual litter production which is a weak function of temperature?
• Temperature sensitivity is limited at the seasonal extremes (summer, winter).
0SdC
dt
Litter production - Soil respirationSdC
dt
Soil respiration Litter production (Ta, P, Rn, fertilizer, …)
Soil carbon pool
Respiration in autumn is much higher than in spring even though temperature is similar between these two seasons.
Seasonal distribution of temperature sensitivity B, (Re=AeBT ).
Spring B is the largest except at the NB site.There is no correlation between T and respiration in winter except at the WB site.
Season
NB
B R2 T
WL
B R2 T
HV
B R2 T
WB
B R2 T
Spring 0.0351 0.47 -5.1 0.0844 0.50 5.2 0.0445 0.38 5.1 0.0632 0.60 13.3
Summer 0.0676 0.36 13.3 0.0526 0.23 16.2 0.0255 0.08 17.0 0.0283 0.10 22.3
Autumn 0.0603 0.83 -1.3 0.0801 0.45 7.8 0.0231 0.18 8.0 0.0547 0.66 14.1
Winter 0.0126 0.08 -21.8 0.0142 0.04 -7.0 0.0283 0.08 -3.3 0.0340 0.46 4.4
Climate variables and NEE at various time scales
(NB, WB, WL, HF)
NEE of CO2 and precipitation
Correlation between NEE and precipitation is very poor on daily, monthly and seasonal time scales.
Correlation becomes strong for interannual time scales.
NEE and precipitation
Northern OBS tower (NB)
Manitoba, Canada
Wofsy, Munger et al.
Boreal black spruce forest
NEE and precipitation
WLEF TV tower (WL)
Northern Wisconsin, USA
Davis, Bakwin et al.
Mixed forest/wetland mosaic
NEE and precipitation
Harvard Forest (HF)
Massachusetts, USA
Wofsy, Munger et al.
Deciduous forest
NEE and precipitation
Walker Branch tower (WB)
Baldocchi, Wilson et al.
Tennessee, USA
Deciduous forest
Climate variables and NEE at various time scales
(NB, WB, WL, HF)
NEE and net radiation
Correlation between NEE and net radiation is strong on all time scales.
NEE and net radiation
Northern OBS tower (NB)
Manitoba, Canada
Wofsy, Munger et al.
Boreal black spruce forest
NEE and net radiation
WLEF TV tower (WL)
Northern Wisconsin, USA
Davis, Bakwin et al.
Mixed forest/wetland mosaic
NEE and net radiation
Harvard Forest (HF)
Massachusetts, USA
Wofsy, Munger et al.
Deciduous forest
NEE and net radiation
Walker Branch tower (WB)
Baldocchi, Wilson et al.
Tennessee, USA
Deciduous forest
Climate variables and NEE at various time scales
(NB, WB, WL, HF)
NEE and PAR
Correlation between NEE and PAR is good on short time scales, and becomes worse on annual time scale.
NEE and PAR
Northern OBS tower (NB)
Manitoba, Canada
Wofsy, Munger et al.
Boreal black spruce forest
NEE and PAR
WLEF TV tower (WL)
Northern Wisconsin, USA
Davis, Bakwin et al.
Mixed forest/wetland mosaic
NEE and PAR
Harvard Forest (HF)
Massachusetts, USA
Wofsy, Munger et al.
Deciduous forest
NEE and PAR
Walker Branch tower (WB)
Baldocchi, Wilson et al.
Tennessee, USA
Deciduous forest
SummarySummary
• Dependence of NEE on climatic factors is not consistent across time scales.
• Net radiation and precipitation become more correlated with NEE on annual time scale.
• Dryness=Rn/(L*P) may be used as an annual controlling parameter on interannual variability of NEE of CO2.
Discontinuous permafrost existsWater stress is not criticalSoil thaw is critical; this depends on Rn
Drought leads to more release of CO2
With abundant soil moisture, available energy is critical for CO2 uptake.As dryness>0.95, water stress becomes critical.1998 is the second year of drought. 1999 is the third year of drought. (?)
Drought has strong effect on interannual variability in NEE at WB.
NB
WL
HV
WB
HV-Harvard Forest (US,92-99)
TH-Tharandt (Germany, 97-99)
WL-WLEF (US, 97-99)
WB-Walker Branch (US,95-98)
NO-Norunda (Sweden,96-97)
LW-Little Washita (US,97-98)
LO-Loobos (Netherlands,97-98)
HL-Howland (US, 96-97)
HE-Hesse (France, 98-99)
Across many sitesAverage per site over several years
Acknowledgements
• Funding and personnel support:– DoE – NIGEC – Midwest and Great Plains– NOAA CMDL– NASA – EOS Validation– DoE – TCP/TECO– NSF/NCAR– USDA-FS