Download The Role of the Bacterioneuston in Air

The Role of the
Bacterioneuston in
Air-Sea Gas Exchange
Emma Harrison
Sea Surface Microlayer
• Widespread, unique and dynamic habitat
covering ~70% of the Earth’s surface
• Microlayer ranges between 1 – 1000 um
(GESAMP 1995)
• Highly debatable and subject to change
through recent years
• Rich and diverse microorganism community
thriving on the interaction between
atmosphere and the water column
Sea Surface Microlayer
•
Main constituents of the organic surface microlayer:
- Lipids (3%)
- Proteins (16%)
- Polysaccharides (30%)
- Humic substances (50%)
•
Extremely exposed to various environmental parameters;
Solar radiation
Fluctuations in temperature, salinity, pH and
nutrients
Toxic substances
•
Increased stress exerted onto microorganisms inhabiting
the microlayer
Bacterioneuston
• The uppermost region of the microlayer (1 um) is
known as the bacterioneuston
• The bacteria occupying this environment are highly
adaptable as extreme environment
• It is estimated that the bacteria present in the
bacterioneuston are 103 - 105 more abundant when
compared to the underlying waters just a few
centimetres below
• Heterotrophic bacteria and methanotrophs widely
distributed in the marine environment but their
diversity is low
Bacterioneuston
•
Various molecular ecology
techniques (PCR) have
been applied to identify
bacterial species in the
bacterioneuston
•
Build up gene libraries
using 16S rRNA gene
probes
•
Dominant bacteria:
Vibrio spp and
Pseudoalteromonas spp
•
Particular emphasis into
the research of Nevskia
ramosa - easily
identified and locally
abundant BUT difficult
to culture
Bacterioneuston Images
Taken from a pond!
Air-Sea Boundary
•
The microlayer and therefore the
bacterioneuston, forms an important
boundary for the exchange of
climatically active trace gases such as
methane, carbon dioxide, carbon
monoxide, nitrous oxide and
dimethylsulphide (DMS)
•
The interface between the microlayer
and the atmosphere is 1000um of the
sea surface and 50-500um of the
atmosphere (GESAMP 1995)
•
Bacterioneuston may therefore exert
important controls on air-sea gas
exchange
•
Consequent effects on air-sea gas
fluxes could be considerable
•
Other factors such as wind velocity
and sea surface state important in
calculating oceanic source and sink of
climatically active trace gases
Project Overview
•
Project in collaboration with the University of Warwick
•
Forms an integral part of the SOLAS (Surface Ocean Lower
Atmosphere Study) Project
•
Focused on the interaction of specific groups of bacteria
(especially methanotrophs) with various trace gases such as
methane
•
To quantify the flux of gases passing between the atmosphere
and ocean
•
Gas transfer velocity, Kw is a kinetic parameter that is estimated
indirectly for inert volatile tracers by measuring the evasive
(water to air) rates of the tracer into the air
- Sulphurhexafluoride (SF6)
•
Can therefore measure a whole host of gases, including methane
and nitrous oxide, invasive (i.e. air to water) and evasive
exchange between the water and the air
Sampling Methods
• Surface microlayer
definition based on the
depth of the sample
layer collected, which
in turn is dependent on
the sampling method
employed
• Also very dependent
on the investigator
• Host of methods for
collecting samples
Sampling
Method
Depth sampled
Paper/
membrane
filters
8-100 um
Screen
sampler
300-400 um
Rotating drum
34-100 um
Glass plate
20-100 um
Teflon plate
50-100 um
Acquiring Bacterioneuston
Samples
Sampling at Blyth Harbour
Equipment
•
Gas exchange tank (closed
system) will be seeded with
various bacteria to enable
quantification of microbial
effects on gas exchange
•
Conditions altered to
provide turbulence and
specific temperatures and
salinities
•
Two gas chromatography
machines to measure the
concentration of gases both
in the water and in the air of
the tank
•
Water bath to maintain a
constant temperature for
water samples extracted
from the tank
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
Acknowledgements
Many thanks to the following…
• Supervisors;
Rob Upstill-Goddard (Newcastle) and Colin
Murrell (Warwick)
• Postdoc; Michael Cunliffe (Warwick) for
the bacterial cultures
• Grant Forster with help on building a new
GC and equipment set-up
• NERC