Gel particles in the sea-surface microlayer during an experimental study

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.自20世纪80年代初以来，海表面微层（sea-surface microlayer, SML）就被假设为一种胶状薄膜。近期研究已证实这一特性，该特性赋予海表面微层介导海洋与大气间物质及能量通量的功能，其中包括海洋系统原生有机气溶胶的排放过程。本研究于2010年9月至12月期间，开展了5组重复室内实验，对海表面微层的厚度与组成进行了探究。每轮实验中，我们从4个海水培养箱中采集海表面微层及其下层海水样本：其中1个为对照组，另外3个分别接种以在恒化器中、于180、380和780 ppm二氧化碳分压（pCO2）条件下培养的威氏海链藻（Thalassiosira weissflogii）。我们对每个培养箱中的有机质富集因子进行了检测，重点关注凝胶颗粒的富集情况，包括多糖性透明胞外颗粒（TEP）与蛋白质类考马斯亮蓝可染色颗粒（CSP）。尽管既往研究已观测到微层中碳水化合物与TEP的富集现象，但目前学界对海表面微层内的蛋白质类凝胶颗粒仍所知甚少。本实验结果表明，CSP是海表面微层胶状组成的主导成分。我们认为，CSP的富集现象暗示了细菌活动在海表面微层中的重要性。细菌可通过其分泌物以及可通过细胞破裂释放的蛋白质组分，在介导海-气界面的相关过程中发挥关键作用。