permafrost soils and their organic carbon...

25.09.2014

1

Permafrost soils and

their organic carbon storage

Laboratory of Ecophysiologiy of Permafrost Systems –

PerSyst

Krasnoyarsk, September 22-24, 2014

Glacier retreat due to warming in the Alps (Aletsch Glacier)

1856 1982 2030

(predicted) www.myswissalps.ch

25.09.2014

2

Mass loss of Greenland ice shield (as analyzed by GRACE)

Wahr, 2013

Analysis of mass changes show dramatic loss of ice shield in SW and E Greenland

Consequences of permafrost soil degradation

Locally: Problems with buildings and technical structures

25.09.2014

3


Regional and longer time scale: Shift of biomes northwards e.g., soil development at mean annual temperature of -8°C, -6°C, and -4°C

Guggenberger and Bussemer (2000)


Globally: Participation at the global carbon cycling

25.09.2014

4

Soil types (Soil Taxonomy) in permafrost regions

Tarnokai et al. (2009)

Soil organic carbon contents in permafrost soils

Tarnokai et al. (2009)

25.09.2014

5

Global Carbon storage

Small changes in the size of the carbon pool within permafrost soils strongly affect the size of the atmospheric CO2 pool

Plant biomass

450 Pg

CO2 atmosphere

750 Pg

Total soils

2400 Pg Permafrost soils

1670 Pg

Sizes of major global carbon pools


Globally: Participation at the global carbon cycling

Conserves soil organic matter

Contains microorganisms

What happens with the organic matter after permafrost thaw?

Permafrost

25.09.2014

6

Photos: Robert Mikutta

Cryoturbated permafrost soils (5-m trenches)

Tussock tundra

Moss-shrub tundra

Cg Cg

Cg

Cg Cg

Cg Cg Ajj

Ajj

Ajj

Ajj Ajj Ajj

Ajj

Ajj

Ajj Ajj

Ajj

AB AB AB AB

Bg Bg Bg Bg

O

O O O

O O Bg1

Bg2

Bg1

Bg2 Bg2

A A O

A A A A

BCg BCg BCg O

O

O

Grass tundra Scale: 50 cm

Photos: Robert Mikutta

Cryoturbated permafrost soils (5-m trenches)

Tussock tundra

Moss-shrub tundra

Cg Cg

Cg

Cg Cg

Cg Cg Ajj

Ajj

Ajj

Ajj Ajj Ajj

Ajj

Ajj

Ajj Ajj

Ajj

AB AB AB AB

Bg Bg Bg Bg

O

O O O

O O Bg1

Bg2

Bg1

Bg2 Bg2

A A O

A A A A

BCg BCg BCg O

O

O

Grass tundra Scale: 50 cm

25.09.2014

7

Example of a cryoturbated soil profile

Soil profile

Soil type (according to Soil Taxonomy): Typic Aquiturbel, fine to coarse loamy (thixotrop)

Morphological features: polygonal cracks, frost boils, cryotrubations Active layer thickness: 65-90 cm

Sketch of soil profile with horizon designations

© Norman Gentsch

kg OC m-2

0 5 10 15 20

So

il d

ep

th (

cm

)

0

20

40

60

80

100

pH (H2O)

5 6 7 8 9

0 5 10 15 20

0

20

40

60

80

100

5 6 7 8 9

Grass tundra

kg OC m-2

0 5 10 15 20

0

20

40

60

80

100

pH (H2O)

5 6 7 8

0 5 10 15 20

0

20

40

60

80

100

5 6 7

Tussock tundra

Frost boil

Depression

Frost boil

Depression

AB

BgAjj

Cg

Cgf

Ajj Cgf

Cgf

Cg

O

Bg1

Bg2

AjjCg

Cfg

Cfg

Oe

Oa

Ajj

Bg2

Cg

Cfg

Cfg

Carbon stocks and variability

AL+PF (100 cm) 33 – 42 kg OC m-2

Permafrost table

kg OC m-2

0 5 10 15 20

Soil

de

pth

(cm

)

0

20

40

60

80

100

pH (H2O)

5 6 7

0 5 10 15 20

0

20

40

60

80

100

4 5 6 7

Moss-shrub tundra

no data

no data

Frost boil

Depression

BCg

A

Ajj

Cg

CfgCfg

CgAjj

Oe

BCg

AL+PF (100 cm) 16 – 47 kg OC m-2

Permafrost table

Gentsch et al. (in preparation)

25.09.2014

8

Carbon stocks and variability

%

0 10 20 30 40 50 60 70

Grass tundra

Tussock tundra

Moss-shrub tundra

Mean (n = 5)

Contribution of OC in Ajj horizons to total OC stocks (100 cm, incl. permafrost)

Very high small-scale variability at profile scale

Subducted OC contributes

on average 20% to the total OC stocks


Functional separation of soil organic matter

Density fractionation to separate unprotected plant residues (particulate OM) from OM protected by formation of mineral-organic complexes (minera-associated organic matter)

density solution

SEDIMENT FLOATING MATERIAL

SOIL

Light fraction

(particulate OM) Heavy fraction

(mineral-associated OM)

25.09.2014

9

Carbon involved in formation of mineral-organic associations

Contribution of OC in mineral-organic associations


% m

inera

l-associa

ted O

C

0

20

40

60

80

100

Ajj

A/AB

B/BCg/Cg

PF

n = 25

n = 10

n = 25

n = 26

Dominating contribution of mineral-bound OM in all studied tundra soils

POM-C contribution on

average <<40% (~ 20%) to total OC.

First indices for organic matter decomposition

Shrubby Grass

C/N

0 10 20 30 40

1

3C

(‰

)

-29

-28

-27

-26

-25

-24

Min

era

l-associa

ted O

C (

% o

f to

tal O

C)

0

20

40

60

80

100

n = 24

n = 9

n = 24

n = 22

Cryoturb. mineral topsoil

Mineral topsoil

Mineral subsoil

Permafrost

Shrubby

Lichen

0 10 20 30 40

Shrubby

Tussock

C/N

0 10 20 30 40

1

3C

(‰

)

-30

-28

-26

BA

Cryoturb. mineral topsoil

Mineral subsoil

Permafrost

Organic soil

Mineral topsoil

C/N ratio versus δ13 C ratio (A) and percentage of mineral-associated OC (B)

Mikutta et al. (under review in EJSS)

25.09.2014

10

O

A, OaAjj

Cgjj

Ajj

Ajj

Cgjj

Cgjj

AB

Oe

Oe

Oa

AB

1 32

Alk

yl-C

/ O

-/N

-Alk

yl C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Alkyl C

O-/N-Alkyl C

Aryl C

Carboxylic C

Organic layer

Topsoil

Cryoturbated topsoil

Subsoil

Mineral-associated OM – 13C NMR spectroscopy

Ketonic/Aldehyde-C

Phenolic/Aryl-C-C

Anomeric/O-alkyl C

Alkyl C

pro

gres

sive

alt

erat

ion

Solid-state 13C NMR spectra of mineral-associated OM from shrubby-grass tundra

Mikutta et al. (under review in EJSS)

Forms of permafrost degradation

Increase in active layer thickness (well-drained mineral soils)

Thermokarst erosion („catastrophic event“)

Lakeshore erosion

River/ coastal erosion

25.09.2014

11

Thermokarst formation

Chronosequence of thermokarst developed on a raised bog Thermokarst are formed in organic and mineral soils (i.e., Yedoma) with restricted drainage

Studies at Little Grawijka Creek (Igarka)

P3

P6 P7

P3 P7

P6

Rodionov et al. (2008)

25.09.2014

12

Typical soils

Active layer > 3 m

Cambisol

Active layer < 100 cm

Mineral Cryosol

Active layer < 60 cm

Organic Cryosol

Active layer thickness

Active layer

< 0.3 m to > 3m

Permafrost degradation

Slopes: Increase in active layer thickness

Bogs: Thermokarst


25.09.2014

13

Soil organic carbon stocks (0-1 m)


Mean OC stock; % in permafrost

NE slope 28 kg C m-2; 31 %

SW slope 22 kg C m-2; 14 %

Intact bog 52 kg C m-2; 68 %

Degraded bog 26 kg C m-2; 0 %


Mean OC stock; % in permafrost

NE slope 28 kg C m-2; 31 %

SW slope 22 kg C m-2; 14 %

Intact bog 52 kg C m-2; 68 %

Degraded bog 26 kg C m-2; 0 %

Soil organic carbon stocks (0-1 m)


Kanonical correlation coefficient cosin2

OC stock Thickness active Layer 5-10 kg m-2 0.94

10-15 kg m-2 0.94

15-25 kg m-2 n.g.

25-50 kg m-2 n.g.

50-100 kg m-2 -0.79


25.09.2014

14

Methane analysis

„Closed chamber“ method

Gas analysis with automated GC system

Soils as methane source and sink

Gut belüfteteBöden

CH4

500

kg

ha-1 a-1

5 kg

ha-1 a-1

Anoxic soilw

Well-drained soils

Net methane exchange between the atmosphere and soils

-120

-80

-40

0

CH

4 f

lux

(g

m-2

) P4 P1 P3 P5 P6

permafrost no permafrost

CH

4 -F

luss

(m

g m

-2)

Terrestrial soils of the forest tundra are methane sinks

Soils without permafrost (net uptake ca. 1.5 kg CH4 ha-1 a-1)

Soils with permafrost (net uptake ca. 0.5 kg CH4 ha-1 a-1) Flessa et al. (2008)

25.09.2014

15

Net methane exchange between the atmosphere and thermokarst

Blodau et al. (2008)

Subhydric

soils; partly with

swimming

grases

P7

Net methane exchange with the atmosphere - thermokarst

Flessa et al. (2008)

Methane exchange of thermokarst lakes with the atmosphere

0

5000

10000

15000 15-Jul 13-Okt 11-Jan 11-Apr 10-Jul

frozen

?

CH

4 (µ

g m

-2 h

-1)

Thermokarst lakes are strong methane sources

25.09.2014

16

Methane exchange with atmosphere Cumulative fluxes related to ha-1

Methane flux: July 2006-August 2007

Thermo-

karst

area

Soils

without

Soils

with

permafrost

CH

4 flu

x (

kg

ha

-1)

Soils without permafrost

Soils with permafrost

Thermokarst

-50

0

50

100

150

200

250


Methane exchange with atmosphere Cumulative fluxes related to m2


-20

0

20

40

60

Pe

rce

nt

dis

trib

uti

on

of

are

a

-40

0

40

80

120

Meth

ane

flux (kg ye

ar-1)

Methane flux in 0.44 km2 sized catchment

Thermokarst represents only 2% of the catchment, but controls the methane emission

25.09.2014

17

Prediction of organic carbon losses due to permafrost thaw?

Studies along climosequences (see Igarka study)

Development with time is replaced by spatial gradient

+ Allows long-time studies

- Also other factors than temperature may differ

Incubation studies

Carry out incubation experiments under controlled conditions

+ Allows detailed comparisons

- Very artificial - Mostly short-term experiments

Soil warming experiments

Manipulation in situ

+ Combination of realistic conditions and control

- Expensive - Mostly short-term experiments

C losses from different permfrost soils during 12-year incubation at 5°C (measured and 3-pool modeled)

Elberling et al. (2013)

Drained grass-

land soil

Heath soil

Wet grass-land soil

Cumu- lative fluxes

25.09.2014

18

C losses (in % of initial C) after 1, 10, and 50 years of incubation at 5°C (note: for 10 and 50 years potential loss)

Schädel et al. (2013)

Organic carbon losses as obtained by 3-pools modeling of data derived from incubation experiments

Cumu- lative fluxes

org: organic soil; min<1 m: shallow mineral soil; min>1m: deep mineral soil

C losses (in % of initial C) related to C:N ratio of initial soil organic matter

Schädel et al. (2013)

Organic carbon losses upon incubation appears to be related to the C:N ratio of the soil organic matter

Note: No information on the quality of the relation is given

25.09.2014

19

Yedoma erosion

Duvannyi Yar exposure on the Kolyma river bank (Vonk et al., 2013)

Photos: Chris Linder

High bioavailability of Yedoma-derived carbon

Dissolved organic carbon loss after 14 (bars) and 28 days (points)dark incubation at 20°C (Vonk et al., 2013)

25.09.2014

20

Projected consequences of climate change n permafrost degradation and carbon emissions

Estimates for permafrost degradation and release of greenhouse gases as CO2 equivalent in four IPCC scenarios (Schuur et al., 2013)

Cumulative carbon emissions projections (Schuur et al., 2013)

T increase: 2.5°C, 7.5°C, 7.5°C

T increase: 1.5°C, 2.0°C, 2.0°C

Shown are values of CO2 and CH4 (Pg) as CO2 equivalents for continuous, dicontinuous, and sporadic permafrost

Projected consequences of climate change on cumulative carbon emissions

25.09.2014

21

Relevance of permafrost soils for global climate

Permafrost soils store about twice as much C as is in the atmosphere as CO2

Conclusions

Organic matter in permafrost soils appears to be vulnerable to decomposition after permafrost thaw

Critical evaluation of experiments

Incubation experiments neglect differences in the environmental conditions of different horizons

Investigations on organic matter stabilization in thawed permafrost soils are almost completely lacking (i.e., impact of mineral-organic complexes, formation of aggregates and subsequent occlusion of organic matter within, increased organic matter input, nutrient stoichiometry, etc.)

Landscape unit (bog vs. mineral soil; undrained vs. drained; exposition, etc.) is a decisive paramter controlling the response of permafrost soils on changing climate

Questions for group work

Group 1 Why are the conditions for microbial decomposition of organic matter better in the topsoil than in the subsoil? List several aspects and give explanations for them. Group 2 Why most permafrost soils are not well aggregated? What might happen if the active layer deepens? Group 3 Which environmental factor leads to the formation of bogs? What happens, if a bog is drained, e.g. by thermokarst erosion? Group 4 Develop a scenario on the consequences of climate warming in mineral permafrost soils with respect to organic matter storage.

25.09.2014

22

O

I will be happy for questions, suggestions, …

Spasibo Thank you

permafrost soils and their organic carbon...

Documents