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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