SUPPLEMENTARY INFORMATION - Nature...(December, January and February) air temperature data...

SUPPLEMENTARY INFORMATIONdoi: 10.1038/ngeo803

nature geoscience | www.nature.com/naturegeoscience 1

ZackenbergZackenberg

Supplementary figure 1S: Zackenberg Research Station in Northeast Greenland.

2 nature geoscience | www.nature.com/naturegeoscience

SUPPLEMENTARY INFORMATION doi: 10.1038/ngeo803

Photo

BE

Heath site

Supplementary figure 2S: Zackenberg m

eteorological station and the heath site near the ZER

OC

ALM 1 active layer thickness

monitoring grid. The vegetation type is dom

inated by C

assiope.



Supp

lem

enta

ry fi

gure

3S:

Zac

kenb

erg

ZER

OC

ALM

2 a

ctiv

e la

yer m

onito

ring

grid

. The

pho

to

illust

rate

s th

e co

ntra

stin

g ve

geta

tion

type

s fro

m w

ell-d

rain

ed h

eath

(Cas

siop

e) to

poo

rly

drai

ned

wet

land

veg

etat

ion.

Wet

land

site



Heath

Wetland

0

20

40

60

80

1001997 1999 2001 2003 2005 2007

Thaw

dept

h(c

m)

Supplementary figure 4S: Permafrost degradation at CALM 2 over 11 years show thawing of about 0.9 cm per year (selected grid points representing the two vegetation types).



ObservationsDMI grid data-downscaledCRU grid data-downscaled

Year

Summer (JJA)

Winter (DJF)

Mea

n m

ontly

air t

empe

atur

e(˚C

)

Supplementary figure 5S: Grid summer (June, July and August) and winter (December, January and February) air temperature data downscaled to Zackenberg used in figure 6 to predict permafrost degradation. Predictions for 2009-2080 are based on a 2 °C global warming over a 100 years period and in white 2.4 °C over a 60 years period.

-30

-25

-20

-15

-10

-5

0

5

10

1900 1930 1960 1990 2020 2050 2080



YearSupplementary figure 6S: Observed and modelled permafrost degradation in Zackenberg 1900-2080 based on downscaled climate data. Predictions are given fortwo vegetation types: wetland (brown), heath (green) and two scenarios: a 2 °C global warming over 100 years (filled symbols) and 2.4 °C over 60 years (open symbols). Running means over 10 years are shown with solid lines.

0.5

0.6

0.7

0.8

0.9

1.01900 1930 1960 1990 2020 2050 2080

ObservationsM

axim

um th

aw d

epth

(m) Wetland

Heath



Supp

lem

enta

ry fi

gure

7S:

Per

maf

rost

cor

ing

in s

umm

er 2

008

a: A

com

plet

e 4

m d

rillin

g eq

uipm

ent r

eady

at

the

heat

h si

te, b

: Tw

o pe

rson

s dr

illing

usi

ng th

eir b

ody

wei

ght t

o fo

rce

the

drill

dow

n an

d a

third

per

son

cont

rollin

g th

e dr

illing

dep

th a

t the

wet

land

site

, c: R

ecov

erin

g th

e fro

zen

perm

afro

st c

ores

from

the

drill

head

afte

r dril

ling

by ro

tatin

g an

d d:

A ty

pica

l ice

-rich

dril

l cor

e fro

m th

e to

p pe

rmaf

rost

.

ab

cd



Photo

HH

C

Supplementary figure 8S: Ice-rich perm

afrostfrom the top perm

afrost at wetland site.



0 40 80 120

160

2000

24

6

Org

anic

carb

on(%

) Depth(cm)

0.0

0.2

0.4

0.6

0.8

1.0

N-to

tal (

%)

010

2030

C:N

(by

wei

ght)

020

4060

8010

0

Wat

eran

d ic

e(%

by

Vol

)

Fen

Hea

th

Supp

lem

enta

ry fi

gure

9S:

Act

ive

laye

r and

per

maf

rost

solid

cha

ract

eris

tics.

Hor

izon

tal l

ines

in

dica

te th

e m

ean

max

imum

act

ive

laye

r dep

th (e

nd o

f Aug

ust 1

997-

2007

) at w

etla

nd (s

olid

) and

he

ath

site

s (d

ashe

d).



050

100

150

200

250 45

67

89

pH

Depth (cm)

050

100150

200250

DO

C (ppm

)10

02

46

8Total dissolved

N (ppm

)01

23

4N

H4 -N

(ppm)

00.5

11.5

2N

O3 (ppm

)

Heath

Fen

Supplementary figure 10S: Active layer and perm

afrostwater/ice characteristics. H

orizontal lines indicate the m

ean maxim

um active layer depth (end of August 1997-2008) at w

etland (solid) and heath sites (dashed).

Heath

Fen



050

100

150

200

250 45

67

89

pH

Depth (cm)

050

100150

200250

DO

C (ppm

)10

02

46

8Total dissolved

N (ppm

)01

23

4N

H4 -N

(ppm)

00.5

11.5

2N

O3 (ppm

)

Heath

Fen

Supplementary figure 10S: Active layer and perm

afrostwater/ice characteristics. H

orizontal lines indicate the m

ean maxim

um active layer depth (end of August 1997-2008) at w

etland (solid) and heath sites (dashed).

Heath

Fen

0 1 2 3

00.

050.

10.

15

00.

002

-0.0

02

Depth (cm)

N2O

(µm

ol L

-1)

N2O

pro

duct

ion

(µm

ol c

m-3

s-1)

Pro

du

ctio

n m

easu

red

po

siti

ve

00.

02-0

.06

05

1015

-0.0

2

00.

40.

8

0-0

.02

0.02

01

23

45 -0.1

0.05

0-0

.05

-0.1

ab

cd

Supp

lem

enta

ry fi

gure

11S

: Obs

erve

d an

d m

odel

ed s

tead

y st

ate

mic

ro-N

2O p

rofil

es in

thaw

ed a

nd m

anip

ulat

ed

perm

afro

st c

ores

from

the

wet

land

site

in Z

acke

nber

g, N

E-G

reen

land

. a: D

rain

ed a

nd re

-sat

urat

ed w

ith

deio

nize

d w

ater

, b: D

rain

ed a

nd re

-sat

urat

ed w

ith d

eion

ized

wat

er a

men

ded

with

glu

cose

, c: D

rain

ed a

nd re

-sa

tura

ted

with

bul

k dr

aina

ge w

ater

from

the

sam

e si

te a

nd d

: Dra

ined

and

re-s

atur

ated

with

dei

oniz

ed w

ater

am

ende

d w

ith g

luco

se a

nd a

mm

oniu

m n

itrat

e. O

bser

ved

N2O

con

cent

ratio

ns s

how

n by

fille

d sy

mbo

ls,

calc

ulat

ed g

radi

ent b

ased

on

PRO

FILE

sho

wn

with

a c

urve

d lin

e an

d th

e co

rresp

ondi

ng p

rodu

ctio

n/co

n-su

mpt

ion

prof

ile s

how

n as

blu

e bo

xes.



0123

Depth (cm)

N2 O

(µmol L

-1)

01

23

45

c

Supplementary figure 12S: O

bserved non-steady state micro-N

2 O profiles in thaw

ed and manipulated

permafrost cores (open sym

bols) from the w

etland site in Zackenberg, NE-G

reenland. a to c: represent time

steps of 12 hours after samples have been drained and re-saturated w

ith bulk drainage water from

the same

site. d: The same sam

ples after steady state conditions have been obtained. Observed N

2 O concentrations

shown by filled sym

bols, calculated gradient based on PRO

FILE shown by a curved line in d.

01

23

45

b

01

23

45

a

01

23

45

d



Supp

lem

enta

ry fi

gure

13S

: Obs

erve

d N

2O e

miss

ion

from

one

col

umn

of th

e ac

tive

laye

r and

upp

er 1

0 cm

pe

rmaf

rost

from

the

wet

land

site

in Z

acke

nber

g, N

E-G

reen

land

. Sc

enar

io 1

is th

e em

issi

on fr

om th

e ac

tive

laye

r mea

sure

d at

7 ºC

wat

er a

nd w

ith th

e bo

ttom

per

maf

rost

sec

tion

plac

ed in

sup

er-c

oole

d -7

ºCw

ater

. Sc

enar

io 2

is th

e em

issi

on fr

om th

e ac

tive

laye

r and

the

perm

afro

st la

yer a

t 7 ºC

. Sce

nario

3 is

the

sam

e as

sc

enar

io 2

but

afte

r the

mel

t wat

er h

as b

een

drai

ned

over

24

hour

s an

d in

ject

ed in

the

low

er 1

0 cm

sec

tion

afte

r 7 d

ays

of in

cuba

tion

at 7

ºC. T

he th

ree

scen

ario

s ha

ve b

een

repe

ated

on

the

sam

e co

lum

n th

ree

times

. Th

e fir

st in

itial

one

is s

how

n as

bla

ck b

ars,

the

seco

nd o

ne in

gra

y an

d th

e fin

al e

xper

imen

t in

whi

te. O

ne

stan

dard

dev

iatio

n of

thre

e re

plic

ates

flux

est

imat

es a

re s

how

n as

ver

tical

lines

.

N2O emission (mg N2O m-2d-1)

010203040

12

3Sc

enar

ios



Supplementary figure 14S: a: Total m

onthly liquid precipitation from 1996 to 2008 and b:O

bserved accum

ulated precipitation (2007 a dashed blue line and 2008 a solid blue line), water table fluctuations (2007

open squares and 2008 filled squares) and active layer development (2007 open triangles and 2008 filled

triangles ) from a w

etland site in Zackenberg, NE-G

reenland during the growing season 2007 and 2008. N

ote the m

arked water table fluctuations in both the fairly dry 2007 grow

ing season and wet 2008 grow

ing season.

0 20 40 60 80

100

19961997

19981999

20002001

20022003

20042005

20062007

2008

September

AugustJulyJune

60 50 40 30 20 10 021-0601-07

11-0721-07

31-0710-08

20-0830-08

09-09 40 80 120

2007 & 2008

ab2008

2007

Monthly liquid precipitation (mm)Water table and active layer (cm)

Accumulated liquid precipitation (mm)



1

Supplementary Methods:

High nitrous oxide production from thawing permafrost

Bo Elberling1,2,3*, Hanne H. Christiansen3, Birger U. Hansen1

1Department of Geography and Geology, University of Copenhagen, DK-1350 Copenhagen,

Denmark

2Department of Biology, The University Centre in Svalbard, UNIS, N-9171 Longyearbyen, Norway.

3Department of Geology, The University Centre in Svalbard, UNIS, N-9171 Longyearbyen, Norway.

*Correspondence: [email protected]



2

Study sites. Zackenbergdalen is a wide valley lowland dominated by Quaternary non-calcareous

sediments with significant periglacial activity and continuous permafrost (S1-S4). The hilltops are

exposed throughout the year with little or no accumulation of snow and thus devoid of vegetation.

The topography and the winter dominant northern wind direction are the main factors controlling

the snow distribution, which is clearly seen at landscape scale, causing a distinct vegetation

zonation from hilltops to depressions. From the hilltops towards the depressions there is an increase

in soil water content from dry conditions at the hilltops to wet conditions at the foot of the slopes

due to snow melt water (S2, S4). Roughly 1/3 of the lowland area in Zackenberg is poorly drained

with expected marked future water table fluctuation due to changes in snow distribution and

duration, permafrost thawing and evapotranspiration during the growing season (S2). Given the

little summer precipitation, water availability during the growing season is mainly controlled by the

location of larger snow-patches melting through the growing season resulting in the dense

vegetation beneath snow patches.

The two study sites were selected to represent two major contrasting dry and wet landforms,

with different plant communities and hydrological conditions representing large parts of the

Zackenbergdalen sedimentary lowland areas. The dry heath site is located on a well-drained marine-

abraded ground moraine dominated by white arctic bell-heather Cassiope tetragona heath. The

Cassiope plants are 5-10 cm tall and the vascular plant cover is about 80%. The most common

herbs are Luzula arctica and L. confusa. The wetland site is located in a poorly drained wetland area

in the lower part of a nivation site with a seasonal and in some years perennial long-lasting snow

patch. The AL is saturated by melt water during large parts of the growing season due to snow

patch melting and some water from thawing of the AL draining to the site. Common species are

Fischer’s tundra grass Dupontia fisheri, fisher’s tundra grass D. psilosantha and white cottongrass

Eriophorum scheuchzeri.



3

Meteorology, climate, active layer and permafrost. Based on data from the meteorological

station located in Zackenberg (1996-2007), the mean annual air temperature is -9.5°C with annual

precipitation varying from 150 to 200 mm (S3). Minimum air temperatures during winter are close

to -40°C, and temperatures 2.5 cm below the soil surface are as low as -18°C for about four months

of the year in the heath study site. AL thickness in the two sites has been monitored in the

ZEROCALM1 (heath site) and ZEROCALM2 (wetland site) grids since 1996) with interannual

variations controlled by meteorology and snow patch duration for the wet site (S4). AL thaw

progression since the summer of 1996 in the ZEROCALM grids shows maximum thawing to occur

in end of August, with variation from 43 cm to 70 cm at ZEROCALM2 (up to 63 cm at the wetter

part representing the wetland area), and from 60 to 80 cm for the heath site.

Climate model simulations from 1900-2080 are based on a regional model developed at the

Danish Meteorological Institute (S5). The regional model is driven by an Atmosphere-Ocean

General Circulation Model, which is based on the HIRHAM4, forced with data from a transient

General Circulation Model simulation with ECHAM5/MPI-OM (S6). The model uses a global 2ºC-

stabilization scenario with estimates of the allowable greenhouse gas concentrations and the

associated climate change. Monthly air temperatures with a spatial resolution of 25 km have been

downscaled to the Zackenberg region (S3) to evaluate current versus future thawing rates. The used

scenario causes a 5°C air temperature increase in the summer period (June, July, August) and an

8°C increase in the winter period (December, January, February) over a 100-year period starting

from 1990. A comparison with air temperature measurements at Zackenberg over the last 12 year

shows a much quicker response, and a scenario with a 6°C increase in the summer period and a

10°C increase in the winter period over a 60-year period is much more realistic, so both scenarios

have been used in the modelling.



4

Analysis. Samples from the AL and permafrost layers from the two study sites with 5 cm intervals

were analysed for total organic C and N using a LECO TruSpec Carbon Nitrogen Determinator for

water and ice content based on mass differences before and after drying.

Sub-samples were drained and the melt water collected and analysed for NO3, NH4 and total

dissolved N (using a FIAstar 5000 flow Analyzer), total dissolved C (Shimadzu Total Organic

Carbon Analyzer TOC-5000A) after 0.45 um filtration. Values of pH were obtained by using a

Metrohm 691-pH meter.

Four replicate sub-samples (3±0.5 g dry weight) from each depth were thawed and within 48

hours quantified with respect to the production of N2O over 24 and 48 hours at 7 ºC. Two of these

replicates were left for 150 days at 7 ºC and the production of N2O reanalysed. The other replicates

were amended with the original drained water. In all cases, gas samples from incubated samples

were transferred using a 3.0-mL venoject vial (Terumo Europe, Belgium) to a Hewlett-Packard

5890 gas chromatograph with an electron capture detector (EDC) to determine N2O concentrations,

which were converted to net N2O productions rates per unit dry soil per hour, taking into account

N2O dissolution (according to S7).

Detailed experimental work. Consumption and production rates of N2O were quantified at five

specific depths intervals at the wetland site representing different ages of the original C and N

sources (63 - 65.5; 82.5 - 85; 115 - 117.5; 171-173.5 and 207-209.5 cm) from the wetland site,

along with detailed measurements of O2, redox and diffusivity. These intact permafrost cores of 2.5

cm in height and 1 cm in diameter were melted, drained to field capacity using a sand bath and kept

under aerobic conditions for seven days. During drainage, the water content varied between 22-33%

by weight and the oxygen concentration in the air above surface reached above 90% of oxygen

saturation. Subsequently, samples were saturated with either A: deionized water, B: deionized with

the addition of glucose (10 mg glucose per g dry soil), C: bulk melt/drainage water from the



5

wetland site (with the following concentrations: 110 ppm DOC, 1.4 ppm NH4-N and 0.9 ppm NO3

and pH of 7.2) and D: finally deionized water with glucose (10 mg glucose per g dry soil) and

NH4NO3-N (0.6 mg ammonium nitrate per g of dry soil). Glucose was applied as an electron donor

for denitrification (S8) and ammonium nitrate to ensure non-limitation of N in both denitrification

and nitrification processes in soils (S9). Finally, extra deionized water was in a few cases added to

ensure at least 5 mm water cover, and samples were finally left for 24 hours with free access to

atmospheric oxygen at 7 ºC, before micro-profiles were initiated as described below.

Oxygen concentrations were measured in the standing water and in the saturated thawed

permafrost samples with a miniaturised Clark-type O2 micro-sensor (OX10, Unisense, Science

Park, DK-8000 Aarhus, Denmark) equipped with an internal reference and a guard cathode (S10).

The output current was measured by a picoampere meter (PA2000, Unisense), which

simultaneously kept the cathode polarised against the internal reference. The sensors had a tip

diameter of 30-80 µm, a stirring sensitivity of <1% and a 90% response time of less than 5 s. The

linearity of the sensor response was confirmed by recording the output current in pA in water

sparged with N2, air and pure O2. The sensor was calibrated at the experimental temperature, using

the output current in the overlying water and in strongly reduced water (alkaline 0.1M sodium

ascorbate solution). Calibration before and after profiling revealed that instrument drift over a few

hours was insignificant. Profiling measurements with oxygen sensors were made at 500 µm depth

intervals controlled either automatically or manually by a micromanipulator. The reference depth

for vertical positioning was determined by approaching the soil surface with the sensor tip in small

steps and moving the sensor horizontally after each step. The highest position at which the sensor

was able to make surface particles move was defined as the sediment surface. Subsequently, the

reference depth was confirmed by a change in the slope of the O2 gradient at the sediment surface.

The observation of the change in slope was the only method of identification of the surface position

during in-situ measurements, as the visual detection was not possible due to the light conditions.



6

Micro-scale diffusivity sensors (Unisense) with a diameter of 200-400 µm were applied to

measure apparent diffusivity of the medium surrounding the sensor tip by measuring concentrations

of a tracer gas in an internal gas reservoir within the sensor tip (S11). The sensor consists of an

outer glass capillary with parallel sides along a silicone plug that fills the sensor tip. Inserted into

the plug is a hydrogen transducer with a tip of 30 µm. A volume behind the membrane is flushed by

hydrogen (H2) mixed with N2. Hydrogen was used as the tracer gas to avoid interference with the

N2O dynamics. A similar set-up using acetylene has previously been used as an inert tracer in

similar diffusivity sensors (S12).

Standard micro-sensors were used to measure N2O concentrations (S13) on the basis of an

ascorbate oxygen trap that quantifies N2O. Sensors with a diameter of 50 µm were applied and a

similar set-up has previously been used (S13; S14).

One entire column 70 cm long and 10 cm in diameter was brought to the laboratory frozen

and thawed at 7 ºC in steps. First the AL and subsequently also the permafrost layer were thawed.

Afterwards, the column was drained and the melt water collected and injected again in the newly

thawed permafrost zone. After each treatment, the net N2O emission was quantified as an increasing

N2O concentration in a closed headspace above the soil surface over 24 hours and repeated three

times over a week using a Hewlett-Packard 5890 gas chromatograph. The entire thawing and

rewetting procedure was repeated three times and the column kept frozen at -7 ºC for a week before

the procedure was repeated.

Modelling. The numerical model PROFIL (S15) was used to analyse measured N2O concentration

profiles and apparent diffusivity. PROFIL calculates the rate of production and consumption as a

function of depth, assuming that the concentration depth profiles represent steady state conditions.

The procedure involves finding a series of least square fits for the measured concentration profile,

followed by comparisons of these fits through statistical F-testing (S15). This approach leads to an



7

objective selection of the simplest consumption profile that reproduces the measured concentration

profiles. The model has been successfully tested against analytical solutions describing the transport

and consumption of O2 in sediment pore water (S15). Based on the calculated production/con-

sumption profiles, the integrated N2O production was estimated and compared to the flux across the

near surface diffusive double layer.

References

S1. Christiansen, H.H. Nivation forms and processes in unconsolidated sediments, NE Greenland.

Earth Surface Processes and Landforms 23, 751–760 (1998).

S2. Elberling, B. et al. Soil and Plant Community-Characteristics and Dynamics at Zackenberg.

Advances in Ecological Research 40, 223-248 (2008).

S3. Hansen, B.U. et al. Present-Day Climate at Zackenberg. Advances in Ecological Research 40,

111-149 (2008).

S4. Christiansen, H.H. et al. Permafrost and Periglacial Geomorphology at Zackenberg, Advances

in Ecological Research 40, 151-174 (2008).

S5. Stendel, M., Christensen, J.H. & Petersen, D. Arctic Climate and Climate Change with a

Focus on Greenland. Advances in Ecological Research 40, 13-43 (2008).

S6. May, W. Towards a global “2 degree C-stabilization” scenario: estimates of the allowable

greenhouse gas concentrations and the associated climatic changes. Danish Climate Centre

Report 06-03 (2006).

S7. Weiss R.F. & Price, B.A. Nitrous oxide solubility in water and seawater. Marine Chemistry 8,

347-359 (1980).

S8. Yu, K., Struwe, S., Kjøller, A. & Chen, G. Nitrous oxide production and consumption

potential in an agricultural and a forest soil. Communications in Soil Science and Plant

analysis 39, 2205-2220 (2008).



8

S9. S. Ullah, R. Frasier, L. King, N. Picotte-Anderson, T.R. Moore, Soil Biology and

Biochemistry, 40, 986-994 (2008).

S10. Revsbech, N.P. An oxygen microelectrode with a guard cathode. Linmology and

Oceanography 34, 474-478 (1989).

S11. Revsbech, N.P., Nielsen, L.P. & Ramsing, N.B. A novel microsensor for determination of

apparent diffusivity in sediments. Linmology and Oceanography 43, 986-992 (1998).

S12. Elberling, B. & Damgaard, L.R. Micro-scale measurements of oxygen diffusion and

consumption in subaqueous sulfide tailings. Geochimica et Cosmochimica Acta 65, 1897-

1905 (2001).

S13. Andersen, K., Kjær, T. & Revsbech, N.P. An oxygen insensitive microsensor for nitrous

oxide. Sensors and Actuators B81, 42-48 (2001).

S14. Revsbech, N.P., Jacobsen, J.P. & Nielsen, L.P. Nitrogen transformations in

microenvironments of river beds and riparian zones. Ecological Engineering 24, 447-455

(2005)

S15. Berg, P., Risgaard-Petersen, N. & Rysgaard, S. Interpretation of measured concentration

profiles in sediment pore water. Linmology and Oceanography 43, 1500-1510 (1998).

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