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Global-scale controls on ocean- atmosphere
ammonia flux
Martin Johnson, Peter Liss, Tim Jickells, Thomas
Bell
Laboratory for global marine and atmospheric
chemistry, School of Environmental
Sciences, University of East Anglia,Norwich, UK
Stuart Gibb
Environmental Research Institute, Thurso, UK
Challenger Marine Biogeochemistry SIG, NUI
Galway, September 2007
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Outline

• Biogeochemical importance
• Measurement aspects
• Previous studies
• Field data from High Latitudes
• Temperature effect
• Seasonal effects
• AMT data
• Global budgets coastal significance
• Interactions with DMS oxidation products

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Ammonia biogeochemical importance

• Most abundant naturally occurring base in the
  atmosphere (one of very few). Neutraliser of
  atmospheric acidity.
• Highly perturbed and poorly quantified vector in
  the global N cycle
• Potentially great significance to global energy
  budget through particle and cloud formation
  (particularly over the remote ocean where
  particle numbers are low)?
• Sea-air/ air-sea flux a sink / source of
  available nitrogen for phytoplankton in the
  surface ocean (probably not a big deal!)?

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Measurement aspects

• Seawater methods OPA fluorimetry (see Holmes
  ref), FIGD-IC (see Gibb ref)?
• Atmospheric methods Acid trapping on filter
  packs (see Johnson 2004 for a critical assessment
  of data quality / sampling and analytical issues.

Gibb, S. W., P. S. Liss and R. F. C. Mantoura,
Ocean-atmosphere exchange and atmospheric
speciation of ammonia and methylamines in the
region of the NW Arabian Sea, Global
Biogeochemical Cycles, 13, 161-178, 1999. Holmes,
R., A. Aminot et al, A simple and precise method
for measuring ammonium in marine and freshwater
ecosystems, Canadian Journal of Fisheries and
Aquatic Science, 56, 1801-1808, 1999. Johnson, M.
T., The Air-sea Flux of Ammonia, PhD Thesis,
University of East Anglia, Norwich, UK, 2004.
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Previous Studies of sea air-ammonia flux

• A positive value represents a flux from sea to
  air
• Only studies making sea-air flux estimates based
  on simultaneous measurements of NHX in the
  atmosphere and ocean considered (others tend to
  be wildly different!)?

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High latitude observations
Johnson, MT, PS Liss, TG Bell, SW Gibb, T
Leswoth, AR Baker, AJ Hind, K Biswas, EMS
Woodward, TD Jickells, Field observations of the
ocean atmosphere exchange of ammonia... Global
Biogeochemical Cycles, submitted.
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Sensitivity analysis
Flux equation F -kg(NH3(g)) KH x
NH3(sw) KH function of T NH3(sw)
NHX(sw) x Ka/(Ka H)? Correction to pKa
(Bell et al 2007)?
Bell, TG, MT Johnson, TD Jickells and PS Liss,
Ammonia / ammonium dissociation coefficient in
seawater a significant numerical correction,
Environmental Chemistry, 4 , 2007
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Sporadic elevated surface concentrations
Martin Johnson, The Air-sea flux of ammonia, PhD
Thesis, University of East Anglia, 2004
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Ammonium in the marine N cycle complex!
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Johnson, M, R Sanders, V Avgoustidi, M Lucas, L
Brown, D Hansell, M Moore, S Gibb, P Liss, T
Jickells, Ammonium accumulation during a
silicate-limited diatom bloom indicates the
potential for ammonia emission events, Marine
Chemistry, 106(1-2), 63-75, 2007
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Johnson, M, R Sanders, V Avgoustidi, M Lucas, L
Brown, D Hansell, M Moore, S Gibb, P Liss, T
Jickells, Ammonium accumulation during a
silicate-limited diatom bloom indicates the
potential for ammonia emission events, Marine
Chemistry, 106(1-2), 63-75, 2007
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AMT observations
Johnson, MT, PS Liss, TG Bell, SW Gibb, T
Leswoth, AR Baker, AJ Hind, K Biswas, EMS
Woodward, TD Jickells, Field observations of the
ocean atmosphere exchange of ammonia... Global
Biogeochemical Cycles, submitted.
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Global budget seasonal, no shelf seas
Martin Johnson, The Air-sea flux of ammonia, PhD
Thesis, University of East Anglia, 2004
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Global budget annual, shelf seas
Martin Johnson, The Air-sea flux of ammonia, PhD
Thesis, University of East Anglia, 2004
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DMS-ammonia interactions
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Conclusions

• Ammonia flux in the remote ocean controlled
  principally by temperature at the global scale
• High latitude ocean a sink for ammonia in spite
  of relatively high concentrations
• Low latitude oceans and oligotrophic gyres
  probably a source in spite of relatively low
  concentrations
• Biological activity can cause significant
  deviation from the annual average
• Shelf seas potentially as big contributors to
  marine ammonia source as open ocean in spite of
  much smaller area
• Southern ocean seasonal flip?
• Unknown effect of reaction with DMS oxidation
  watch this space

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Acknowledgements

• Andy Hind, Tim Lesworth, Karabi Biswas, Alex
  Baker, Richard Sanders, Mark Moore, Louise Brown,
  Mike Lucas, Valia Avgoustidi, Stuart Painter for
  supporting data
• NUI Galway, Rachel Cave and Martin White for
  having us
• Quaternary QUEST / GENIEfy projects for financial
  support to attend

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