Fayetteville Green Lake (FGL) is a recognized, extensively studied present‐day model of the stratified Proterozoic ocean. Nonetheless, biomass sedimentation in FGL remains hard to explain: while virtually all sediment pigments belong to photosynthetic sulfur bacteria from a chemocline, the isotopic carbon signature of the bulk organic matter suggests its epilimnetic phytoplankton origin. To explain the epilimnetic origin of sedimented carbon, we studied the dominant Synechococci, isolated from FGL. Here, we present experimental evidence that FGL Synechococci produce copious extracellular polysaccharides (EPS) especially when availability of inorganic carbon (C_i) is high relative to availability of other macronutrients, for example phosphorus. The accumulating EPS become impregnated with calcium, magnesium, and sodium cations and are released to the environment as ballasted cell coverings. Sedimentation of these cell‐free EPS can constitute the bulk of pigment‐free organic material in FGL sediment. Because increased availability of C_i specifically stimulates production of EPS and the accumulated EPS adsorb cations and become ballasted, we propose the universal role of cyanobacterial EPS in biomass sedimentation in the high‐C_i Paleoproterozoic ocean as well as in modern aquatic systems like FGL.

中文翻译：

---

me陷的费耶特维尔绿湖中压载无细胞EPS的沉淀。

费耶特维尔绿湖（FGL）是当今公认的层状元古代海洋模型，目前已得到广泛研究。尽管如此，FGL中的生物质沉积仍然难以解释：尽管实际上所有沉积物色素都属于趋化索的光合硫细菌，但大部分有机物的同位素碳特征表明其是浮游浮游植物的起源。为了解释沉积碳的上表层起源，我们研究了从FGL中分离出的主要Synechococci。在这里，我们提供实验证据，证明FGL Synechococci会产生大量的细胞外多糖（EPS），尤其是当无机碳（C _i）相对于其他大量营养素（例如磷）的利用率而言较高。累积的EPS会被钙，镁和钠阳离子浸渍，并作为压载的细胞覆盖物释放到环境中。这些无细胞EPS的沉淀物可能构成FGL沉积物中大部分无色素的有机物质。由于C _i的可用性增加特别刺激EPS的产生以及积累的EPS吸附阳离子并被压载，因此我们提出了蓝细菌EPS在高C _i古元古代海洋以及现代水生系统（如FGL）中的生物质沉降中的普遍作用。