Coastal marine methyl iodide source and links to new particle formation at Cape Grim during February 2006

Michael R. Grose; Jill M. Cainey; Andrew McMinn; John A. E. Gibson

doi:10.1071/EN07008

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Coastal marine methyl iodide source and links to new particle formation at Cape Grim during February 2006

Michael R. Grose ^A ^C , Jill M. Cainey ^B , Andrew McMinn ^A ^C and John A. E. Gibson ^A

+ Author Affiliations

- Author Affiliations

^A Institute of Antarctic & Southern Ocean Studies, Private Bag 77, Hobart, Tas. 7000, Australia.

^B Cape Grim Baseline Air Pollution Station, 159 Nelson Street, Smithton, Tas. 7330, Australia.

^C Corresponding author. Email: mgrose@utas.edu.au

Environmental Chemistry 4(3) 172-177 https://doi.org/10.1071/EN07008
Submitted: 25 January 2007 Accepted: 3 May 2007 Published: 22 June 2007

Environmental context. Emissions of methyl iodide of a biological origin from inshore and coastal waters can be an important component of the atmospheric budget of iodine. Iodine from this and other sources is important in the natural ozone cycle in the troposphere and stratosphere, and may play a role in the formation of new small particles that can then grow to seed clouds. The specific coastal ecology at each location is important to the magnitude and characteristics of this methyl iodide source.

Abstract. Methyl iodide concentration in seawater and in the air directly above the sea was measured at an inshore site adjacent to the Cape Grim Baseline Air Pollution Station (Cape Grim BAPS) near a bed of Bull Kelp (Durvillaea potatorum) over daylight cycles and along a transect out to 5 km offshore. Most inshore samples had low and variable methyl iodide concentrations in seawater (14.8–57.7 pM) and in air immediately above the sea (2.1–3.8 parts per trillion by volume), with a partial tidal influence. A period of elevated methyl iodide concentration in the water (144.5 pM) and in air above the sea surface (5.5 pptv) was immediately followed by a measurement of new particles at the Cape Grim BAPS. This correlation provided indirect evidence that emission of methyl iodide from kelp is connected to the new particle formation pathway, but there was no evidence of a direct causal link. Elevated levels of atmospheric methyl iodide were not detected at the station (adjacent to the site but on top of a 94-m cliff) at the same time, which suggests the effect was localised above the sea surface. A rapid decrease of methyl iodide out to 5 km suggested that a source at the coastal reef was greater than from pelagic phytoplankton; this source could be the intertidal kelp beds.

Additional keywords: aerosols, biogenic production, halogen compounds, kelp, marine chemistry, methyl iodide.

Acknowledgements

The authors acknowledge the contribution of the following people. David Oram and Claire Reeves (UEA) for the GC-ECD system, Paul Viney for boat support, Paul Armstrong for assistance with kelp surveying, Melita Keywood and John Gras for particle data, CSIRO for nutrient analysis, and all the staff of Cape Grim BAPS.

References

Coastal marine methyl iodide source and links to new particle formation at Cape Grim during February 2006

Acknowledgements

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