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Speculation on the origin of sub- baseline excursions of CH 4 at Cape Grim GMAC 2016, Boulder, Colorado Zo Loh | Research Scientist 17 May 2016 OCEANS & ATMOSPHERE Co-authors O&A: Paul Krummel, Rebecca Gregory, Paul Steele,

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Speculation on the origin of sub- baseline excursions of CH4 at Cape Grim

GMAC 2016, Boulder, Colorado

OCEANS & ATMOSPHERE

Zoë Loh | Research Scientist 17 May 2016

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Co-authors

  • O&A:
  • Paul Krummel, Rebecca Gregory, Paul Steele, Marcel van der Schoot, Darren

Spencer, David Thornton, Bronwyn Dunse and Ian Galbally

  • O&A/University of Bristol:
  • Ann Stavert
  • Cape Grim BoM staff:
  • Jeremy Ward and Nigel Somerville + all those at Casey in recent years
  • ANSTO
  • Scott Chambers and Alastair Williams

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Continuous methane data: Cape Grim

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Continuous methane data: Cape Grim & Casey

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Sub-baseline methane excursions

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Sub-baseline methane excursions

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CRDS and GC-FID measurements

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Cape Grim methane residuals: 2013

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  • Intrusions of stratospheric air

– Expect ozone to be anti-correlated with methane during the event

  • Long range transport around the Southern Ocean

– ‘Dynamic isolation’? – Look at the radon & trajectories

  • Marine boundary layer chlorine radical attack

– Look at the correlation with ethane

Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Possible mechanisms

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

June 2013: Ozone

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

June 2013: Radon

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

June 2013: Ethane

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

December 2013: Ozone

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

December 2013: Ethane

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

December 2013: Propane

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

December 2013: Radon

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Trajectories

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  • Intrusions of stratospheric air

– Wintertime seems to have some of these type of events

  • Long range transport around the Southern Ocean

– Radon is sub 100mBq.m-3, but not notably lower, however; – Trajectories do look to be long range SO transport

  • Marine boundary layer chlorine radical attack

– Depleted ozone, ethane and propane

Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Possible mechanisms

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Conclusions

  • Sub-baseline excursions of CH4
  • Do not (all) seem to be due to stratospheric intrusions
  • Possibly long range transport over the Southern Ocean – dynamic isolation
  • Possibly chlorine radical depletion of methane
  • Do similar events occur at Casey?
  • If so, they are much smaller in magnitude. Does this tell us anything?... Mean

latitudinal OH or source of MBL chlorine radical?

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O&A Zoë Loh Research Scientist t +61 2 9239 4518 e zoe.loh@csiro.au w www.csiro.au

OCEANS & ATMOSPHERE

Thank you

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Residuals at Casey

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Synoptic conditions: 13 Dec 2013

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

Synoptic conditions: 16 Dec 2013

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Speculation on the origin of sub-baseline excursions of methane at Cape Grim

December 2013: Hydrogen

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Australian Greenhouse Gas Observation Network

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  • Cape Grim
  • Gunn Point – tropical site
  • Burncluith & Ironbark – coal seam

gas fugitives

  • Macquarie Island (LoFlo only)
  • Casey Picarro G2301
  • RV Investigator G2301 & Aerodyne

N2O/CO

  • Arcturus & Otway (CCS)

decommissioned