Abstract Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids thought to be predominantly produced on land. They are used as a terrestrial paleothermometer based on an empirical relation between their molecular composition and air temperature in surface soils worldwide. The proxy has been applied in continental margin sediments based on the assumption that all brGDGTs originate from land and are transported to marine sediments predominantly by rivers. However, this assumption has been challenged by the discovery of in situ brGDGT production in the coastal marine environment. To better understand marine brGDGT production, we examined newly collected marine surface sediments from the Krossfjorden and Kongsfjorden in Svalbard with a chromatography method to separate previously co-eluting 5- and 6-methylated brGDGT isomers. ‘Living’ intact polar lipid (IPL)-derived and ‘fossil’ core lipid (CL) brGDGTs were also studied for a subset of fjord sediments. The relative proportion of cyclopentane moieties in tetramethylated brGDGTs, used as indicator for brGDGT production in coastal marine settings, is much higher in the fjord sediments (#ringstetra = 0.65–0.93 for CL and 0.24–0.79 for IPL-derived brGDGTs) compared to those in nearby soils (#ringstetra = 0.00–0.37), and confirms the predominantly marine source of the brGDGTs in the fjord. Surprisingly, however, IPL-derived brGDGTs have a substantially lower #ringstetra (up to 0.52 offset) compared to that of CL-brGDGTs in the same sediment. This suggests that brGDGTs are produced in situ in different distributions throughout the year, of which the CL distribution in the sediment is an integrated signal. The offset in #ringstetra between IPL-derived and CL brGDGTs varies between 0.15 and 0.52 and increases towards the open ocean, possibly linking brGDGT production to the natural salinity gradient and associated microbial community changes.

中文翻译：

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海洋领域支链四醚的生产：重新审视斯瓦尔巴峡湾沉积物

摘要支化甘油二烷基甘油四醚 (brGDGTs) 是被认为主要在陆地上生产的细菌膜脂。根据其分子组成与全球表层土壤中气温之间的经验关系，它们被用作陆地古温度计。基于所有 brGDGT 源自陆地并主要通过河流运输到海洋沉积物的假设，该代理已应用于大陆边缘沉积物。然而，这一假设受到了在沿海海洋环境中原位 brGDGT 生产的发现的挑战。为了更好地了解海洋 brGDGT 生产，我们使用色谱方法检查了从斯瓦尔巴群岛的 Krossfjorden 和 Kongsfjorden 新收集的海洋表层沉积物，以分离先前共流出的 5- 和 6- 甲基化 brGDGT 异构体。还研究了一部分峡湾沉积物的“活的”完整极性脂质 (IPL) 衍生和“化石”核心脂质 (CL) brGDGT。四甲基化 brGDGT 中环戊烷部分的相对比例，用作沿海海洋环境中 brGDGT 生产的指标，在​​峡湾沉积物中要高得多（#ringstetra = 0.65-0.93 CL 和 0.24-0.79 用于 IPL 衍生的 brGDGTs）与那些相比在附近的土壤中（#ringstetra = 0.00–0.37），并证实了峡湾中 brGDGT 的主要海洋来源。然而，令人惊讶的是，IPL 衍生的 brGDGT 的 #ringstetra（高达 0. 52 偏移）与相同沉积物中的 CL-brGDGT 相比。这表明 brGDGTs 在全年不同分布中原位产生，其中沉积物中 CL 分布是一个综合信号。IPL 衍生的和 CL brGDGT 之间#ringstetra 的偏移在 0.15 和 0.52 之间变化，并且朝着公海增加，可能将 brGDGT 的产生与自然盐度梯度和相关的微生物群落变化联系起来。