The Role of the Bacterioneuston in Air-Sea Gas Exchange

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The Role of the Bacterioneuston in Air-Sea
Gas Exchange

• Emma Harrison
• University of Newcastle-upon-Tyne, UK

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Bacterioneuston??
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Sea Surface Microlayer

• Widespread, unique and dynamic habitat covering
  70 of the Earths surface
• Microlayer ranges between 1 1000 µm
• Definition highly debatable
• Rich and diverse community of microorganisms
  which thrive on the interaction between the
  atmosphere and the water column

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Extreme Environment?
?
?
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Bacterioneuston

• Bacteria tolerant to this extreme environment
• Estimated that the bacteria present in the
  bacterioneuston are 103 - 105 more abundant when
  compared to subsurface waters
• Preliminary data obtained from North Sea, UK, has
  suggested bacterioneuston dominated by
• - Vibrio sp
• - Pseudoalteromonas sp
• BUT
• This is not necessarily the case everywhere!

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Why is the bacterioneuston important?
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Interactions with the Air-Sea Boundary

• Many exchanges take place across the
• air-sea boundary
• The interface between the microlayer and the
  atmosphere is 1000 µm of the sea surface and
• 50-500 µm of the atmosphere
• Consequently, effects of this boundary on
• air-sea gas fluxes of GREENHOUSE GASES could
  be considerable

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• Microbial metabolism of climatically active trace
  gases such as CH4, N2O, CO, DMS and methyl
  halides in the bacterioneuston may exert
  important controls on
• air-sea gas exchange
• Determining the diversity, abundance and activity
  of the major groups of microorganisms in the
  bacterioneuston and their involvement in trace
  gas cycling are a high priority in the UK SOLAS
  projects

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Research Aims

• Specific objectives
• To determine the bacterial community structure of
  the bacterioneuston with specific reference to
  bacteria that metabolise trace gases
• Investigate the role of the microbial populations
  on gas exchange rates in controlled laboratory
  gas exchange tank experiments
• To measure rates of invasive (i.e. air to water)
  and evasive (i.e. water to air) air-sea exchange
  of selected atmospheric trace gases
• Project in collaboration with Warwick University,
  UK

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Objective OneAnalysis of the bacterial
community structure of the bacterioneuston

• Bacterioneuston sampled by sterile, polycarbonate
  filters
• Removes the top layer of water from the interface
  through surface tension
• Construct gene libraries representative of the
  microbial community by use of 16S rRNA sequence
  data
• Application of PCR and DGGE allows the study of
  these complex communities
• Overcomes
• - small sample size
• - poor culturability of neuston bacteria

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Acquiring Bacterioneuston Samples
Sampling at Blyth Harbour, North East England
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Microbial Community Structure From Blyth Harbour
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Microbial Community Structure From Blyth Harbour

• Bacterial community structure in the microlayer
  is distinct when compared to the subsurface
  waters
• This is also true for Archaea and Eukarya

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Objective TwoRoles of the bacterioneuston
investigated through gas exchange tank

• Purpose built gas exchange tank
• Closed system
• The microbial community structure will be
  correlated with changes in the gas exchange rates
  
• Conditions altered and experiments will use local
  seawater (North Sea), river water (River Tyne),
  Milli-RO and artificial seawater prepared in
  Milli-RO

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Objective ThreeMeasure the invasive and evasive
rates of atmospheric trace gases

• Coupling of two gas chromatographs with gas tank
  to create a fully automated system to measure
  CH4, CO, N2O and SF6 concurrently
• Tank headspace circulated through gas
  chromatographs
• Gas fluxes quantified by estimating their
  transfer velocities, kw
• Estimate kw by measuring evasion rates of inert
  volatile tracer, SF6 with Schmidt number based
  scaling for each individual trace gas

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Conclusion

• Knowledge of the biology and population structure
  within the bacterioneuston is still in its
  infancy
• Unclear what role these microorganisms play
• Is clear the sea surface microlayer has the
  potential to impact the cycling of reactive trace
  gases and the exchange rate of these gases across
  the air-sea boundary
• Using a combination of molecular ecology
  techniques and an understanding of gas exchange,
  the knowledge of this unique and dynamic
  environment will be greatly improved

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Acknowledgements

• Many thanks to the following
• Supervisors
• Rob Upstill-Goddard (University of Newcastle)
• Colin Murrell (University of Warwick)
• Michael Cunliffe (University of Warwick) for his
  support and advice on molecular ecology and for
  microbial community structure work
• Grant Forster for technical assistance
• UK SOLAS Project
• Natural Environment Research Council, UK