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

1. 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 Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey, UK Facility for Airborne Atmospheric Measurements (FAAM), Cranfield University, Cranfield, Bedford MK43 0AL, UK Presented at the: MOCA Kick-off Meeting, Oslo, 29 Oct 2013

2. Methane Isotope Measurements in and Above the Arctic Region Aims of this work • Improve characterisation of the boreal wetland methane isotopic source signature – does it vary by wetland type / location / season? • Measure the methane source signature above the European Arctic for different air masses to calculate the isotopic signature of air arriving from different regions • 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

3. Global CH4Sources –IsotopicFingerprinting 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 RHUL data unless stated. dD data from Sowers (2006)

4. 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

5. Air Sampling for Methane Isotopic Measurements at Royal Holloway 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 CH4concentration measurements by Picarro G1301 CRDS and triplicate d13C measurements by CF-GC-IRMS. Stainless steel or glass flasks are used for sites where CO2, CO and H2 measurements are also required

6. Pine forest fire (ON, Canada) -28‰ ∞ 10000 5000 3333 2500 2000 1667 Methane Sources in the Arctic Spring 2009 Bulk Arctic signature -53‰ Summer 2008 Bulk Arctic signature -65‰ Gas field (Ob River, Russia) -49‰ Hydrate (W. Spitsbergen slope) -51‰ Wetland (N. Finland) -69‰ Thermokarst lakes (Walter et al., 2006) -83 to -58 ‰

7. Arctic CH4d13C at Background Stations Pallas Zeppelin ALT ZEP • δ13C measured in flasks and bags collected at Alert, Zeppelin, Pallas • Weekly bags now also collected at Sodankylä (50m on tower) PAL Alert Late summer/autumn elevated CH4 depleted in 13C at Pallas. Source signature -72‰ – regional wetland sources

8. Isotopic Signature of Methane at Pallas Pallas and Alert, 2009 June-October (2011/2012) 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

9. Back Trajectory Analysis for Svalbard Area Sampling, 2008 (Fisher et al., 2011) 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?) CH4 mixing ratio δ13C (‰) Can miss sudden synoptic changes when sampling is weekly

10. 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) The isotope signatures and the chamber flux measurements can be used to calculate a flux weighted mean source signature: -67.9 ± 2.9‰ -53 ‰ -67 ‰ -70 ‰ -76 ‰

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

12. Keeling Plots to Determine Source Isotopic Signature of Wetland Emissions in Northern Scandinavia in July 2012 Kaamanen -71.7‰ Sodankylä -69.1‰ Faerdesmyra -72.5‰ Lompolojänkkä -71.3‰

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

14. Spatial Variability of CH4 and d13C 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

15. Summer 2011

16. JCR (July) and Geomar Cruises (Sept, 2012) Possible wetland input

17. Summer 2012 Norwegian coastal samples – 21-22 July

18. July to Sept – 2011/12 Keeling Comparison 2011 JCR Svalbard – Scotland transect Very similar source composition dominating excess methane in the high European Arctic for the summers of 2011 and 2012 2012 JCR + Geomar cruises – Iceland – Norwegian Sea - Svalbard 2011 Zeppelin station daily sampling

19. Kjolnes July 2012 Road Trip Pallas

20. 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

21. 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 FGGA The response time from air inlet to data screen is currently 4 seconds for the FGGA and 1 second for the QCL Calibration Pump FAAM core chemistry instrumentation rack installed in mid-cabin

22. 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

23. Finnish Wetlands From Above – Aug 2013

24. 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) B A Source -71.2 ± 0.7 ‰ (R2 = 0.98)

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

26. MEVALI Campaign (March 2012) - All Flights Wetlands frozen, so no wetland component in the CH4 increment

27. Isotopic Signature of Methane Sources by Latitude • 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 Arctic Winter – dominated by gas leaks and heating S-SW winds N-NE winds

28. 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 d13C 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