Measurement of the Isotopes of Methane in the Arctic – from Micro to Macro Scale

Dave Lowry1, Rebecca Fisher1, James France1, Mathias Lanoisellé1, Rebecca Brownlow1, Euan Nisbet1, Axel Wellpott2, Stéphane Baugitte2

1 Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey, UK

2 Facility for Airborne Atmospheric Measurements (FAAM), Cranfield University, Cranfield, Bedford MK43 0AL, UK

Presented at the: MOCA Kick-off Meeting,

Oslo, 29 Oct 2013

Methane Isotope Measurements in and Above the Arctic Region

Aims of this work1) Improve characterisation of the boreal wetland methane isotopic

source signature – does it vary by wetland type / location / season?2) Measure the methane source signature above the European Arctic for

different air masses to calculate the isotopic signature of air arriving from different regions

3) Which scale of measurement is best for regional and global modelling of methane emissions – micro or macro?

This includes a range of scales and platforms:• Long-term records for background monitoring stations in the Arctic• Chamber studies in wetlands• Diurnal sampling of air at low levels over wetlands• Collection on mobile platforms – ships, cars and planes

Global CH4 Sources –Isotopic Fingerprinting

-80

-60

-40

-20

0

13C

H4

/ ‰

-400-350-300-250-200-150-100

D / ‰

Coal Gas Emission Rice Paddies Wetland (bogs + tundra) Landfill Natural Gas Clathrates Biomass Burning C4 Biomass Burning C3 Ruminants C4 Ruminants C3

RHUL data unless stated.D data from Sowers (2006)

Measurements made at source or within plumes coming from them

Big errors on source signatures lead to even bigger errors when modelling the distribution of sources at regional or global scale

The Keeling Plot Method

Plots δ 13C vs 1/CH4 conc. (Usually from samples within / near a source)

Assumes “added methane is all from the same source” and “background is constant”

y-intercept is effectively the point where “added methane = infinite concentration

y-intercept = methane source signature in terms of δ 13C

Air samples are collected in 3 or 5L Tedlar bags using small battery operated pumps, allowing low cost air sampling.

CH4 mixing ratios are stable in the bags even if stored for several months.

This provides enough air for triplicate CH4 concentration measurements by Picarro G1301 CRDS and triplicate 13C measurements by CF-GC-IRMS.

Stainless steel or glass flasks are used for sites where CO2, CO and H2 measurements are also required

Air Sampling for Methane Isotopic Measurements at Royal Holloway

0 0.0001 0.0002 0.0003 0.0004 0.0005 0.0006

-85

-80

-75

-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

1/[CH4] (ppb-1)

δ13C

(‰)

[CH4] (ppb)

Methane Sources in the Arctic

Methane source Reference δ13C (‰)

Wetland, N. Finland Sriskantharajah et al., 2012 -69 to -66Wetland, Hudson Bay Lowlands, Canada Kuhlmann et al., 1998 -60 ± 3.2

Tundra, Alaska Quay et al., 1988 -73 to -55Wetland, Siberia Sugawara et al., 1996

Kuhlmann et al., 1998Meth MonitEUr, 2005

-75 to -67-69.5 ± 15-69

Ebullition from thermokarst lakes, N. Siberia Walter et al., 2006 -83 to -58

Marine clathrate, Haakon Mosby mud volcano

Milkov, 1998; Lein et al., 1999; Ginsburg et al., 1999

-61.9 to -56

Marine clathrate, W. Spitsbergen Fisher et al., 2011 -53 to -46Onshore hydrate, Mackenzie delta, Canada Lorenson et al., 1999 -48.7 to -39.6

Ob River gasfield emissions Meth MonitEUr, 2005 -51 to -48Boreal forest fires, Ontario + NWT, Canada RHUL, unpublished -28.5 ± 1.0

Wetland(N. Finland) -69‰

Summer 2008 Bulk Arctic signature -65‰

Gas field (Ob River, Russia) -49‰

Thermokarst lakes (Walter et al., 2006) -83 to -58 ‰

Pine forest fire (ON, Canada) -28‰

Hydrate (W. Spitsbergen slope) -51‰

Spring 2009 Bulk Arctic signature -53‰

∞ 10000 5000 3333 2500 2000 1667

AlertArctic CH4 13C at Background Stations

• δ13C measured in flasks and bags collected at Alert, Zeppelin, Pallas

• Weekly bags now also collected at Sodankylä (50m on tower)

Zeppelin Pallas

ALT

ZEP

PAL

Late summer/autumn elevated CH4

depleted in 13C at Pallas. Source signature -72‰ – regional wetland sources

Isotopic Signature of Methane at Pallas

0.0005 0.00051 0.00052 0.00053 0.00054

-49

-48.5

-48

-47.5

-47

-46.5

-46

1/CH4 (ppb-1)

δ13C

(‰)

Intercept of a geometric mean regression gives a methane isotopic source signature of -72 ± 2 ‰Matches the wetland signature measured in the ground based and aircraft campaigns

June-October (2011/2012)Pallas and Alert, 2009

23/08/08 30/08/08 06/09/08 13/09/08 20/09/08 27/09/081720

1740

1760

1780

1800

1820

1840

1860

1880

1900

-48.2

-48

-47.8

-47.6

-47.4

-47.2

-47

-46.8

-46.6

-46.4CH4 mixing ratiod13C

CH4

mix

ing

ratio

in

air s

ampl

es (p

pb)

δ13C

(‰)

Back Trajectory Analysis for Svalbard Area Sampling, 2008 (Fisher et al., 2011)

CH4 mixing ratio

δ13C (‰)

4th – 8th September highest methane mixing ratio: Air passed over Ob river area, NW Siberia. Keeling plot for these days gives δ13C source signature = -61 ± 3 ‰ (40% gas leak, 60% wetland?)

Can miss sudden synoptic changes when sampling is weekly

Wetland Chamber Measurements, Sodankylä

Methane collected in 17 chambers had an isotopic source signature ranging from -76 to -53 ‰Emission rates in the chambers over wetland ranged from 0.2 to 11.6 mg CH4/m2/h (flux measurements by CEH Edinburgh)

-53 ‰ -67 ‰ -70 ‰ -76 ‰

The isotope signatures and the chamber flux measurements can be used to calculate a flux weighted mean source signature: -67.9 ± 2.9‰

-50 to -54 -55 to -59 -60 to -64 -65 to -69 -70 to -74 -75 to -800

1

2

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9

Source signature of CH4 in chamber (‰)

Num

ber o

f cha

mbe

rs

0 2 4 6 8 10 12 14

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-75

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CH4 flux (mg CH4 m-2 hr-1)

CH4

sour

ce si

gnat

ure

(‰)

Methane Isotopic Composition of Emissions from Lompolojänkkä Mire, Pallas, Finland (Sriskantharajah et al., 2012)

Keeling Plots to Determine Source Isotopic Signature of Wetland Emissions in Northern Scandinavia in July 2012

Sodankylä-69.1‰

Kaamanen-71.7‰

Faerdesmyra-72.5‰

Lompolojänkkä-71.3‰

Is there a latitudinal gradient in the isotopic signature of CH4 from wetlands in Lapland?

Spatial Variability of CH4 and 13C at High Latitudes - Ship and Road Trip Sampling Campaigns

• Cruises – JCR 253 (July-Sept 2011) – UK - Svalbard hydrate zone - UK– Catarina (June-July 2012) – Porto to Newfoundland via Greenland– JCR 269b (July 2012) – Reykjavik - Svalbard hydrate zone –

Reykjavik– GEOMAR (Aug-Sept 2012) – Rejkjavik - Svalbard hydrate zone –

Bremerhavn• Road trips

– July 21-22, 2012 – Kiruna – Sodankyla – Kaamanen – Kiruna– Sept 9-11, 2012 – Sodankyla – Kaamanen – Berlevag – Tana –

Sodankyla– Aug 17-17, 2013 – Kiruna – Narvik – Alta – North Cape – Berlevag

– Kaamanen – Sodankyla – Lulea - Kiruna

Summer2011

JCR (July) and Geomar Cruises (Sept, 2012)

Possible wetland

input

Summer 2012

Norwegian coastal samples – 21-22 July

July to Sept – 2011/12 Keeling Comparison2011 JCR Svalbard

– Scotland transect

2011 Zeppelin station daily sampling

2012 JCR + Geomar cruises – Iceland – Norwegian Sea

- Svalbard

Very similar source composition dominating excess methane in the high European Arctic for the summers of 2011 and 2012

July 2012 Road Trip

Kjolnes

Pallas

Lapland Road Trip (July 21-22, 2012)

• Moving with the airmass from NW to SE

• 40-50 ppb increase in CH4 associated with a 0.4 to 0.5 ‰ depletion in 13C from the Norwegian coast

• 20 ppb enhancement next to wetland hotspots in Finland around Sodankyla

• Keeling plot for 1.5 days under the same weather system indicates that the source of this excess methane (-70 ‰) is wetland

Measurements and Sample Collection on the FAAM BAE-146 Research Aircraft

• The aircraft is equipped with Los Gatos FGGA (FAAM) and more recently an Aerodyne QCL (Univ. Manchester) for continuous measurement of atmospheric CH4 during the flights

FAAM core chemistry instrumentation rack installed in mid-cabin

FGGA

Pump

Calibration

The response time from air inlet to data screen is currently 4 seconds for the FGGA and 1 second for the QCL

MAMM – Flight Campaigns• Summer flying at 75 and 150m

over wetlands in Finland and Sweden

• Use FGGA and QCL display to choose sample collection times

• Flights linked to ground-based sampling at chamber, wetland and road-trip scale

Finnish Wetlands From Above – Aug 2013

Low Level Flying Over Wetland Areas, August 2013: B797

Concentration range in WAS bottles: 1851 to 1961 ppb

Highest concentration, lowest δ13C (1961 ppb, -48.5 ‰ measured at points A and B)

Source -71.2 ± 0.7 ‰(R2 = 0.98)

A

B

0.5 0.51 0.52 0.53 0.54 0.55

-49.0

-48.5

-48.0

-47.5

-47.0

-46.5

1/CH4 (ppm-1)

δ13C

(‰)

August 2013 WAS Data (Flights B795-800)• Combining all the flight data up to 1500m over Lapland this summer

gives a single correlation suggesting that wetland is the only source for the methane increment during that campaign

• Compared with flight B720 (2012 wetland flight below 1500m) the source signature is the same but the error is much smaller in 2013

0.505 0.51 0.515 0.52 0.525 0.53 0.535 0.54 0.545

-49.0

-48.5

-48.0

-47.5

-47.0

-46.5

1/CH4 (ppm-1)

δ13C

(‰)

Source -71.5 ± 0.4 ‰(R2 = 0.94, n = 155)

MEVALI Campaign (March 2012) - All Flights

70

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Latit

ude

252015Longitude

700600500400300200100

[HC

OO

H] pptv

-1

Wetlands frozen, so no wetland component in the CH4 increment

Isotopic Signature of Methane Sources by Latitude

S-SW winds

N-NE winds

Arctic Winter – dominated by gas leaks and heating

• All information gathered so far from our and North American wetland studies suggest that the signal coming from Canadian wetlands is -63 ± 3‰, but the signal from Scandinavian and Siberian wetlands is much lower, averaging -70 ±3‰. Different vegetation types in the mires might be important in this variation as the Abisko diurnal suggests.

• Are wetland emissions from Lapland becoming lighter? -68‰ in 2008/9 to -71‰ in 2012/13. Check rainfall / wetland areas. Less oxidation.

• The only regional enriched source (-28 ‰) are forest fires and these are very sporadic in timing and rarely influence the isotopic signal in this region

Which Isotopic Measurement Scale Provides the Best Data for Regional and Global Modelling?

• Chambers sample emissions from very small areas which target different water table and vegetation types therefore the 13C is too variable for large scale modelling

• Long-term fixed site records provide a good test of the performance of models, but not data for model input

• Flights provide the best spatial coverage and an averaged isotopic signature for the boundary layer, but are expensive and difficult to plan to fit with the best weather conditions for emissions

• Cruises are rarely close to the methane source regions unless hydrate unexpectedly destabilizes

• A combination of road trips and diurnal sampling at source provide good regional data coverage and confirmation of the contributors to the excess CH4