Abstract Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are thought to be produced by as yet unknown bacteria on land, and their distribution in soils, peats, and lake sediments has been shown to correlate with mean annual air temperature (MAAT). Recently, an increasing number of studies have shown that in situ production of brGDGT in marine environments is likely. However, the influence of environmental factors on marine-derived brGDGT distributions is still unknown. In this study, we assessed the sources of brGDGTs preserved in a sediment core from the Chukchi Sea shelf using multiple brGDGT-based indices, including the branched and isoprenoid tetraethers (BIT) index, the ratio of IIIa/IIa, cyclization degree of branched tetraethers (CBT), and #rings indices, and discuss the influence of seawater temperature changes over the last 70 years on the distribution of brGDGT isomers. The low BIT and CBT values, high IIIa/IIa ratios, and significant correlations between different #rings indices suggest that these brGDGTs primarily have a marine source. With increasing sea surface temperatures (SSTs), the fractional abundances of 5-methyl IIIa (IIIa5) showed an increased trend, while there was no obvious trend in 6-methyl IIIa (IIIa6). This finding indicates different behaviors of 5- and 6-methyl isomers in marine-derived brGDGTs, similar to what has been observed in soils, peats and lakes. In addition, we found a significant correlation between IIIa5 and IIIa7 (a novel isomer of IIIa), indicating that they might share the same bacterial source and/or are controlled by the same environmental factors (e.g., temperature). Finally, the fractional abundances of IIIa5 and IIIa7 are significantly correlated with SST (r2 = 0.64 and 0.49, respectively), which suggests that marine-derived brGDGTs have the potential to reconstruct seawater temperature.

中文翻译：

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楚科奇海陆架沉积物芯中海洋来源的 brGDGT 异构体的不同温度依赖性

摘要支链甘油二烷基甘油四醚 (brGDGTs) 被认为是由陆地上未知的细菌产生的，它们在土壤、泥炭和湖泊沉积物中的分布已被证明与年平均气温 (MAAT) 相关。最近，越来越多的研究表明，在海洋环境中原位生产 brGDGT 是可能的。然而，环境因素对海洋衍生的 brGDGT 分布的影响仍然未知。在这项研究中，我们使用多个基于 brGDGT 的指数，包括支链和类异戊二烯四醚 (BIT) 指数、IIIa/IIa 的比率、支链四醚的环化度，评估了保存在楚科奇海陆架沉积物核心中的 brGDGT 的来源(CBT) 和 #rings 指数，并讨论了过去 70 年海水温度变化对 brGDGT 异构体分布的影响。低 BIT 和 CBT 值、高 IIIa/IIa 比率以及不同 #rings 指数之间的显着相关性表明这些 brGDGT 主要来自海洋。随着海面温度（SSTs）的升高，5-甲基IIIa（IIIa5）的丰度分数呈增加趋势，而6-甲基IIIa（IIIa6）的丰度分数没有明显的增加趋势。这一发现表明海洋衍生的 brGDGT 中 5- 和 6- 甲基异构体的不同行为，类似于在土壤、泥炭和湖泊中观察到的行为。此外，我们发现 IIIa5 和 IIIa7（IIIa 的新型异构体）之间存在显着相关性，表明它们可能共享相同的细菌来源和/或受相同的环境因素控制（例如，温度）。最后，IIIa5 和 IIIa7 的丰度分数与 SST 显着相关（分别为 r2 = 0.64 和 0.49），这表明源自海洋的 brGDGT 具有重建​​海水温度的潜力。