The role of bacterioneuston in air-sea microlayer biogeochemistry of organic matter

The seawater surface is the direct site of air-sea interactions and as such, the properties of the surface ocean may greatly influence the exchange of gases, heat and particles between the ocean and the atmosphere. Hydrophobic organic molecules are concentrated at the surface of the water to form the air-sea microlayer (ASML) that has been shown to harbour a different microbial community (bacterioneuston / BN) relative to the underlying water. Current methods of measuring biological properties of the ASML involve the initial removal and collection of BN. We propose to use a glass tube horizontally half immerged in surface water and sliced sideward through an intact ASML before being corked with two silicone bungs to become an incubation apparatus. The main aim of this proposed research is to develop a method capable of measuring metabolic rates of BN in the intact ASML, using radioisotopically labelled fatty acid tracers. Labelled gaseous metabolites of fatty acids will be collected by bubbling air through headspace of apparatuses and into traps selectively capturing CO2 or tritiated water. Because BN may influence physicochemical processes across the intact ASML, the effect on evaporation rates will be examined using tritiated water as a tracer. Comparisons will be made with samples where BN are not present, BN have been poisoned and samples where the ASML including BN has been removed with the aid of an ultra-thin nitrocellulose membrane. BN cells will be specifically stained with water-repellent dyes to separate them from planktonic cells using a cell sorting device / a flow cytometer. BN cells will be identified microscopically by selective labelling with taxon-specific molecular probes. These methods will be tested initially on marine bacterial cultures before using local seawater samples. It is anticipated that the methods and apparatus developed could be eventually used to measure BN metabolic rates in the intact oceanic ASMLs. The determined biogeochemical fluxes will be compared with physicochemical fluxes through the ASML to advance current understanding of the air-sea interface processes which affect global climate change.