The Role of Bacterioneuston in Air-Sea Gas Exchange

Summary

The sea surface microlayer, including the bacterioneuston, forms an important boundary for the air-sea exchange of trace gases and its unique biological, chemical and physical properties may have considerable impacts on global biogeochemical cycles. There is now increasing evidence, including that from preliminary data here at Newcastle, of a role for the bacterioneuston in processing climatically active trace gases such as methane, carbon monoxide, methyl bromide, DMS and methanesulfonic acid (MSA), a potential precursor of cloud condensation nuclei. Determining the diversity, abundance and activity of the major groups of microorganisms in the bacterioneuston and their involvement in gas exchange, is therefore crucial in understanding this unique environment. The consequent effects on air-sea fluxes of trace gases could be considerable, which is why their study is a high priority within SOLAS, both in the UK and internationally.

It is now well established that bacterial numbers are considerably greater (up to 104 fold) in the bacterioneuston layer than in the subsurface waters. Recent advances in the application of molecular biology to microbial ecology mean that it is now possible to overcome small sample size and poor culturability of neuston bacteria. The use of 16S rRNA sequence data to monitor the dynamics of bacterial community structure without the need for cultivation is now well established. Application of the polymerase chain reaction (PCR) in molecular ecology and denaturing gradient gel electrophoresis (DGGE) makes feasible the study of complex communities.

Accurately quantifying the air-sea fluxes of reactive trace gases relies on accurately estimating their gas transfer velocities. The community structure of the bacterioneuston layer will therefore be correlated with the changes in gas exchange rates measured, and the influence various marine bacteria have on gas exchange rates will be assessed.

Aims

The main aim of this proposal is to test the hypothesis that the bacterioneuston plays an important role in influencing air-sea gas exchange of atmospheric trace gases. The specific objectives are;

  1. To determine the bacterial community structure of the bacterioneuston with specific reference to bacteria that metabolise methane, carbon monoxide, methyl bromide, methyl chloride and DMS.
  2. To measure the rates of invasive and evasive air-sea exchange of atmospheric trace gases and to investigate the role of the microbial populations on gas exchange rates in controlled laboratory gas exchange tank experiments.

 

The results of this project will therefore provide fundamental data on;

  1. The bacterial composition of the bacterioneuston and subsurface water.
  2. The spatial, regional and seasonal dynamics of bacterioneuston communities.