Observations of methane over the Arctic Ocean

Transcription

1 Observations of methane over the Arctic Ocean Stephen Platt1, Cathrine Lund Myhre1, Sabine Eckhardt1, Ignacio Pisso1, Norbert Schmidbauer1, Ove Hermansen1, Andreas Stohl1, Benedicte Ferré2, Anna Silyakova2, Pär Jansson2, Sunil Vadakkepuliyambatta2, Jürgen Mienert2 1 NILU Norwegian Institute for Air Research PO Box 100, 2027 Kjeller, NORWAY 2 Centre for Arctic Gas Hydrate, Environment and Climate Department of Geology UiT The Arctic University of Norway P.O. box 6050 Langnes, 9037 Tromsø, Norway

2 Methane in the Arctic Location of the Zeppelin Observatory Methane at the Zeppelin Observatory -ebas.nilu.no Methane (CH 4 ) is 28 times more powerful than CO 2 as a greenhouse gas Methane is monitored continually at Zeppelin (78.91 N, E, altitude 476 m) by NILU since 2001, hourly Levels rising both globally and in the Arctic at an increasing rate since /5/2018 sp@nilu.no 2

3 The ocean as a methane source Ubiquitous methane seeps at the sea bed release dissolved methane or bubbles ( flares ). Bubbles reaching the surface do not normally contain methane; it dissolves in the water column Arctic polar view including areas m deep Hydrates (methane in ice) form below ~300 m in the Arctic at these seep sites Major concern: the zone where hydrates are stable is retreating due to global warming, a potential feedback if methane reaches the atmosphere 2/5/2018 sp@nilu.no 3

4 The methane from the Arctic Ocean to the atmosphere (MOCA) project Aim: Quantify the present atmospheric effects of methane from gas hydrates at the seabed, and future potential climate impacts on decadal to centennial timescales. Tracking methane from seabed to atmosphere Collaboration between NILU, CAGE (Centre for Arctic Gas Hydrates, University of Tromsø) and other national and international partners funded by NRC Interdisciplinary, combines atmospheric observations and models with oceanography and geology Multi-platform (ship: RV Helmer Hanssen, plane, Zeppelin Observatory, ocean measurements) -Myhre et al., /5/2018 4

5 Overview of measurements Schematic of the Helmer Hanssen Route of the Helmer Hanssen CH 4 and CO 2 collected online continuously since June 2014 at 1 minute resolution using a cavity ring-down spectrometer (Picarro) Covered huge area of Arctic during all cruises operated by CAGE/ UiT -Platt et al., in Prep Data are quality controlled using automatic routines with CO 2 as a tracer for ship exhaust and manual inspection, publicly available at ebas.nilu.no 2/5/2018 sp@nilu.no 5

6 Intensive measurements in summer 2014 Study area Measurements at Prins Karls Forland b) Atmospheric methane over flares Combined atmospheric observations (plane and ship) at oceanography (CTD stations) -Myhre et al., 2016 Surprisingly, no increased methane observed over active flares (purple points), and no methane in surface waters over flares. Variation only around +/- 2ppb 2/5/2018 6

7 Flux constraints via the FLEXPART atmospheric transport model Example of a FLEXPART footprint sensitivity Using FLEXPART we can model how long the air has spent over the ground and for how long Footprint sensitivity: darker=more effect of an emission for that region This is a numerical data field (here 0.1 by 0.1 degrees, hourly) from which we can calculate the expected change in concentration for a given emission (or the other way around if we know the change in concentration) 2/5/2018 sp@nilu.no 7

8 Flux constraints via the FLEXPART atmospheric transport model Modelled emissions (orange) from potential seeps vs. observed methane (green) We can see no change in methane: we instead set the change in concentration to the observed variation of 2 ppb (i.e. calculate a constraint) Assume this change is due to emission from the blue area -Myhre et al., 2016 Of the order of maximum % of the global methane burden (while only the change in this number over time is important for climate change) 2/5/2018 sp@nilu.no 8

9 Why are the ocean-atmosphere fluxes so low? Because the surface concentrations are low Low water column mixing rates often suggested as a cause (pycnocline) However, methanotrophic bacteria are incredibly efficient, e.g nmol L -1 day -1 following Deep Water Horizon 2/5/2018 sp@nilu.no 9

10 Longer term observations Three model emission scenarios Route of the FAAM -Pisso et al., 2016 Repeat the previous exercise, but with 3 different areas For Zeppelin and RV Helmer Hanssen we used all of 2015 (FAAM flights only short duration) Again only low fluxes could be constrained for all scenarios, 63, 37, and 18 Gt Yr -1 for scenarios a, b, c (above) 2/5/2018 sp@nilu.no 10

11 So where does Arctic methane come from? Modelled high latitude methane emissions We combine FLEXPART footprints with emissions according to inventories Mainly Russian oil and gas, Western European agriculture and waste Wetlands important in Summer -Platt et al., in Prep 2/5/

12 Validating the model and explaining long term observations Long term time series Using all available data it is possible to investigate all peaks in the methane concentration time series Zeppelin time series informs whether highly localised at the ship or regional CO2 whether anthropogenic (increases with CH4) or wetland (decreases, in summer) Emissions whether the peak is likely terrestrial in origin All are remarkably well explained by terrestrial emissions except for one unexplained peak on /5/2018 -Platt et al., in Prep 12

13 Validating the model and explaining long term observations Location of Helmer Hanssen and methane concentrations around Large increase in methane directly over previously identified flare region Meteorological conditions were unique; highly localised, stagnant air, i.e. instruments were sensitive to emissions at relatively low levels Suggests at least sporadic releases to the Atmosphere are possible (must still fit within previously determined annual constraints) -Platt et al., in Prep 2/5/

14 Conclusions Summer 2014 and longer term measurements indicate CH 4 release from seabed sediments around Svalbard substantially increases CH 4 concentrations in the ocean, but not in the atmosphere North of Svalbard is an area where ocean-atmosphere fluxes may occur and merits further study Present day fluxes are low. This does not mean that they will stay this way, and so such baseline measurements as these are required 2/5/2018 sp@nilu.no 14

15 THANK YOU References The EBAS database: ebas.nilu.no Myhre, C. L., Ferré, B., Platt, S. M., Silyakova, A., Hermansen, O., Allen, G., Pisso, I., Schmidbauer, N., Stohl, A., and Pitt, J.: Extensive release of methane from Arctic seabed west of Svalbard during summer 2014 does not influence the atmosphere, Geophysical Research Letters, 43, , Pisso, I., Myhre, C. L., Platt, S., Eckhardt, S., Hermansen, O., Schmidbauer, N., Mienert, J., Vadakkepuliyambatta, S., Bauguitte, S., and Pitt, J.: Constraints on oceanic methane emissions west of Svalbard from atmospheric in situ measurements and Lagrangian transport modelling, Journal of Geophysical Research: Atmospheres, 121, Acknowledgments MOCA- Methane Emissions from the Arctic OCean to the Atmosphere: Present and Future Climate Effects is funded by the Research Council of Norway, grant no CAGE Centre for Arctic Gas Hydrate, This work was partly supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number We thank the captain and the crew of Helmer Hanssen for their support during the Arctic cruise CAGE esticc - escience Tool for Investigating Climate Change in northern high latitudes, Nordic Center of Excellence funded by Nordforsk, grant no /5/2018 sp@nilu.no 15