Arctic ecosystems as key biomes in climate-carbon feedback. Hanna Lee Climate and Global Dynamics Division National Center for Atmospheric Research

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1 Arctic ecosystems as key biomes in climate-carbon feedback Hanna Lee Climate and Global Dynamics Division National Center for Atmospheric Research

2 Outline Permafrost carbon Permafrost carbon-climate feedback cycles Thermokarst influence on permafrost carbon feedback cycles Using CLM to better represent permafrost processes 2

3 Warming in the Arctic Northern Hemisphere: 0.4ºC increase in the past two decades IPCC (2007) Arctic: 1.2ºC increase in the past two decades ACIA (2004)

4 Biogeochemical consequences - Permafrost C Permafrost 1672Pg Carbon stored in permafrost 1/2 of global soil C stock x 2 more than C in the atmosphere Thawed permafrost will release C-based greenhouse gases at a faster rate! Schuur et al BioScience Tarnocai et al GlobalBiogeochemCyc 4

5 Why permafrost carbon? Permafrost carbon (1600) adapted from U.S. DOE, Biological and Environmental Research Information System 5

6 Vulnerability of permafrost C Permafrost Zone Soil C Gelisol Soil Order (3m) Permafrost C Loss Current Land Use Change 818 Pg x % Pg ( Pg/yr) (1.5±0.5 Pg/yr) Schuur et al Nature 459:

7 Potential Arctic-climate feedback Global warming + Positive feedback Arctic warming CO 2 uptake by Plant growth Permafrost thaw Soil N Decomposition CO 2 CH 4 7

8 Arctic shrub growth and tree line expansion Photo from the Chandler River located at ' N, ' W: 7/4/1948 and 7/29/2001. (Tape et al., 2006). 8

9 Potential Arctic-climate feedback - Negative feedback CO 2 uptake by Plant growth Global warming Arctic warming Permafrost thaw CO 2 CH 4 9

10 The effects of N fertilization on shrub growth Toolik lake Long-Term Ecological Research site N fertilization over 20 years Warming & thawing permafrost stimulated decomposition and release N back to very N limited ecosystem 10

11 Potential Arctic-climate feedback - Negative feedback CO 2 uptake by Plant growth Global warming Arctic warming CO 2 CH 4 Permafrost thaw Soil N Decomposition 11

12 Physical consequences - Thermokarst formation Land surface subsidence created by permafrost thaw Changes in local hydrology: Aerobic vs. Anaerobic -> C cycling 12

13 Aerobic/Anaerobic influence on permafrost carbon and climate feedback Atmospheric feedback CO 2 > CO 2 /CH 4 > CO 2 /CH 4 Faster decomposition Aerobic Aerobic Anaerobic Anaerobic Warming Permafrost carbon 13

14 Aerobic/Anaerobic influence on permafrost carbon and climate feedback Atmospheric feedback CO 2 < CO 2 /CH 4 << CO 2 /CH 4 Greater GWP Aerobic Aerobic Anaerobic Anaerobic Warming Permafrost carbon 14

15 Climate effects from permafrost C release Laboratory incubation Aerobic Anaerobic Deep permafrost C release under aerobic and anaerobic conditions : Faster C release under aerobic conditions Modified from Lee et al GCB 15

16 Climate effects from permafrost C release Laboratory incubation Aerobic Anaerobic Deep permafrost C release under aerobic and anaerobic conditions : Comparable in atmospheric forcing with CH 4 effect Modified from Lee et al GCB 16

17 Research Questions How does permafrost thaw influence ecosystem carbon balance under warmer world? What is the climate feedback from permafrost C? 17

18 Research Question 1. How does permafrost thaw influence ecosystem carbon balance under warmer world? 18

19 Interior Alaska tundra site Denali National Park 2003 aerial photo 19

20 Interior Alaska tundra site Deep permafrost T increase Natural gradient of permafrost thaw and thermokarst development Osterkamp & Romanovsky 1999 PPP Three sites: Minimal Thaw: Typical tussock tundra before thawing Moderate Thaw: yrs of permafrost thaw Extensive Thaw: over 50 yrs of thaw and deep thermokarst Denali National Park 2003 aerial photo 20

21 Ecosystem carbon cycling Photosynthesis Plant respiration GPP: photosynthetic uptake Reco: respiratory release NEE: GPP - Reco Litter Plant root respiration Microbial respiration CO 2 Soil Organic Matter

22 Aboveground carbon balance CO 2 uptake: GPP Autochambers Balance: NEE CO 2 release: R eco Temporally explicit measurements 22

23 Belowground permafrost carbon release Aboveground CO 2 flux measurement Soil Flux Chambers CO 2 Soil Gas Wells CO 2 Chambers: Photosynthetic uptake Plant respiration Permafrost carbon release CO 2 CO 2 CO 2-10cm -20cm -30cm Gas wells: Root respiration Permafrost carbon release CO 2-40cm Belowground CO 2 measurement 23

24 Aboveground Net Ecosystem Exchange of carbon Balance between carbon uptake and release Net Ecosystem Exchange (gc m -2 ) C sink: More uptake C source: More release Minimal Moderate Extensive Over 3 years: Minimal neutral Moderate = sink ( GPP, R eco ) Extensive = source ( GPP, R eco ) Modified from Schuur, Vogel, Crummer, Lee, Sickman, Osterkamp 2009 Nature 459: Vogel, Schuur, Trucco, Lee 2009 J Geophys Res 114, G4, doi: /2008jg

25 Belowground permafrost carbon release More CO 2 release in Extensive thaw Minimal Thaw Moderate Thaw Extensive Thaw Permafrost C release greater with more permafrost thawing Lee et al JGR

26 C ( ) Depth (cm) Respiration Partitioning using 14 C 14 CO 2 14 CO 2 14 CO 2 14 CO Atmosphere Minimal Thaw Moderate Thaw Extensive Thaw Young 14 C ( ) Old Bomb signature Natural decay Organic matter deposit 26

27 14 C ( ) C ( ) Depth (cm) Respiration Partitioning using 14 C 14 CO 2 14 CO 2 14 CO 2 14 CO Atmosphere Minimal Thaw Moderate Thaw Extensive Thaw Young C ( ) Old 200 Bomb signature 100 Natural decay 0 Organic matter deposit Recent detritus Plant respiration Old soil C 27

28 Ecosystem Respiration (g C m -2 yr -1 ) More old carbon loss with permafrost thaw Minimal Thaw Moderate Thaw Extensive Thaw R 2 = Old Carbon Loss (%) Contribution of permafrost C in total ecosystem C release greater with more thawing. Schuur, Vogel, Crummer, Lee, Sickman, Osterkamp 2009 Nature 459:

29 Surface patterns under thawing permafrost Land surface before thawing 29

30 Surface patterns under thawing permafrost Relative subsidence up to 1.2 m Dryer/Colder Wetter/Warmer Land surface subsidence with thawing Wetter and warmer 30

31 Surface patterns under thawing permafrost Relative subsidence up to 1.2 m Dryer/Colder Wetter/Warmer Land surface subsidence with thawing More CO 2 Lee et al JGR Wetter and warmer More subsided Relative subsidence 31

32 How can we model ecosystem C dynamics with thermokarst? Sampling Spatially explicit measurements Land surface patterns Ecosystem C balance Vegetation Soil environment 5m apart 50 pts each site Extensive Thaw 50m 32

33 UTMy How can we model ecosystem C dynamics with thermokarst? Lee et al GCB Land surface patterns Minimal Thaw Low relief land surface pattern Variability in surface patterns Moderate Thaw Extensive Thaw UTMx High relief land surface pattern 33

34 78 How can we model ecosystem C dynamics with Carbon release Carbon uptake thermokarst? UTMy Annual Reco Annual GPP Lee et al GCB Land surface patterns UTMy Minimal Thaw Minimal Thaw Moderate Thaw Moderate Thaw Extensive Thaw UTMx Extensive Thaw Land surface patterns explain ecosystem carbon balance in the landscape! UTMx 34

35 Insights from Observations Permafrost thaw increase C uptake, but increase C release at a greater rate over time Land surface subsidence (thermokarst) can be used as a proxy for understanding ecosystem C balance on a landscape scale 35

36 Potential Arctic-climate feedback - Negative feedback Early stage of thawing CO 2 uptake by Plant growth Global warming Arctic warming Expanded wetlands CO 2 CH 4 Lakes drain, soils dry Permafrost thaw Soil N Decomposition 36

37 Potential Arctic-climate feedback Later stage of thawing Global warming + Positive feedback Arctic warming CO 2 uptake by Plant growth Expanded wetlands Permafrost thaw Soil N CH 4 Decomposition CO 2 Lakes drain, soils dry 37

38 Permafrost Carbon Loss in global carbon context Using the three sites as representatives of permafrost thaw Permafrost Zone Soil C Gelisol Soil Order (3m) Permafrost C Loss Current Land Use Change 818 Pg x % Pg ( Pg/yr) (1.5±0.5 Pg/yr) Schuur, Vogel, Crummer, Lee, Sickman, Osterkamp 2009 Nature 459:

39 Research Question 2. What is the climate feedback from permafrost C? 39

40 Using Earth System Models Community Earth System Model, NCAR 40

41 Near surface permafrost extent Lawrence and Slater 2005 Lawrence, Slater, Swenson

42 Conceptual diagram of Community Land Model 4.0 Diffuse solar Emitted longwave Downwelling longwave Latent heat flux Sensible heat flux Reflected solar Absorbed solar Aerosol deposition SCF Soil (sand, clay, organic) Bedrock Surface fluxes Soil heat flux Precipitation Momentum flux Wind speed 0 u a Evaporation Dust Sublimation Melt Soil Aquifer recharge Unconfined aquifer Transpiration Throughfall Water table Hydrology Evaporation Infiltration Saturated fraction Sub-surface runoff Surface runoff Phenology Fire Biogeochemical cycles Photosynthesis Soil C/N Vegetation C/N Litterfall N mineralization BVOCs Heterotrophic respiration Root litter N uptake Autotrophic respiration N dep N fixation Denitrification N leaching Glacier Lake Urban Wetland River discharge Wood harvest Runoff River Routing Land Use Change Competition Vegetation Dynamics Disturbance Growth Lawrence et al., Journal Advances Modeling Earth Systems,

43 Observations Model 43

44 Improvements in Community Land Model 4.5 Diffuse solar Emitted longwave Downwelling longwave Latent heat flux Sensible heat flux Reflected solar Absorbed solar Aerosol deposition SCF Soil (sand, clay, organic) Bedrock Surface fluxes Soil heat flux Precipitation Momentum flux Wind speed 0 u a Evaporation Dust Transient layer that acts like permafrost Sublimation Melt Soil Aquifer recharge Unconfined aquifer Hydrology Transpiration Throughfall Water table Evaporation Infiltration Surface runoff Wetlands Permafrost layer Saturated fraction Sub-surface runoff Phenology Fire Biogeochemical cycles Photosynthesis CO BVOCs 2 /CH 4 dynamics Soil C/N Vegetation C/N Litterfall N mineralization Heterotrophic respiration Root litter N uptake Autotrophic respiration N dep N fixation Denitrification N leaching Glacier Lake Urban Wetland River discharge Wood harvest Runoff River Routing Land Use Change Competition Vegetation Dynamics Disturbance Growth Lawrence et al., Journal Advances Modeling Earth Systems,

45 Excess ice and thermokarst parameterization Ice wedges in permafrost soil Problem in CLM Agriculture & Agri-Food Canada Anaerobic environment CO 2 /CH 4 emissions Exposed permafrost CO 2 emissions Government of Yukon Thermokarst development

46 Excess ice and permafrost parameterization Soil layers and Excess ice Control Excess ice Melting Surface subsidence CLM4.5 Ice and soil mixture at layers 8-10 Control: Regular CLM soil layers 46

47 Thermokarst predictions under future climate projections Unit: meter Lee et al. in prep Env Res Lett 47

48 Improved model and climate feedback Global warming Arctic warming CO 2 uptake by Plant growth Expanded wetlands Permafrost thaw Soil N CH 4 Decomposition CO 2 Lakes drain, soils dry Enhanced predictions of Arctic-climate feedback with improved models 48

49 Conclusions Permafrost C important and underestimated source of C in terrestrial-climate feedback Thermokarst development can influence the rate and types of C release Models are improving to better represent permafrost processes under changing climate 49