Abstract
Since the early 80’s, the sea-surface microlayer (SML) has been hypothesized as being a gelatinous film. Recent studies have confirmed this characteristic, which confers properties that mediate mass and energy fluxes between ocean and atmosphere, including the emission of primary organic aerosols from marine systems. We investigated SML thickness and composition in five replicate indoor experiments between September and December 2010. During each experiment, the SML and underlying seawater were sampled from four seawater tanks: one served as control, and three were inoculated with Thalassiosira weissflogii grown in chemostats at 180, 380 and 780 ppm pCO2. We examined organic material enrichment factors in each tank, paying particular attention to gel particles accumulation such as polysaccharidic Transparent Exopolymer Particles (TEP) and the proteinaceous Coomassie Stainable Particles (CSP). While previous studies have observed carbohydrates and TEP enrichment in the microlayer, little is yet known about proteinaceous gel particles in the SML. Our experiments show that CSP dominate the gelatinous composition of the SML. We believe that the enrichment in CSP points to the importance of bacterial activity in the microlayer. Bacteria may play a pivotal role in mediating processes at the air-sea interface thanks to their exudates and protein content that can be released through cell disruption.
Highlights
The sea-surface microlayer (SML) is a specific and dynamic ecosystem at the water-air interface
This study investigated the upper 150 μm of the water column in order to understand the composition of the SML with respect to bulk water as a result of phytoplankton and bacterial activity
Enrichment of the microlayer was found in the particulate organic matter fraction to which bacterial cells and gel particles contribute
Summary
The sea-surface microlayer (SML) is a specific and dynamic ecosystem at the water-air interface. The SML is susceptible to modification by photochemical reactions, wind-driven atmospheric deposition, water circulation and biological activity: it can be a simultaneous sink and source of natural and anthropogenic compounds [1]. It includes a complex matrix of organic material and microorganisms that at times may form slicks, lowering seawater surface tension and influencing air-sea gas and energy exchange [2,3,4]. The SML can be operationally defined as a several-layer structured microhabitat between 1 and 1000 μm thick: it has been proposed to study physicochemical characteristics in the upper 60 μm, and species dependent biological and ecological features over the upper 1000 μm [1]
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