In order to reconstruct the ecosystem structure of chemosynthetic environments in the fossil record, geochemical proxies must be developed. Here, we present a suite of novel compound-specific isotope parameters for tracing chemosynthetic production with a focus on understanding nitrogen dynamics in deep-sea cold seep environments. We examined the chemosymbiotic bivalve Bathymodiolus childressi from three geographically distinct seep sites on the NE Atlantic Margin and compared isotope data to non-chemosynthetic littoral mussels to test whether water depth, seep activity, and/or mussel bed size are linked to differences in chemosynthetic production. The bulk isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N), and δ¹⁵N values of individual amino acids (δ¹⁵N_AA) in both gill and muscle tissues, as well as δ¹⁵N_AA-derived parameters including trophic level (TL), baseline δ¹⁵N value (δ¹⁵N_Phe), and a microbial resynthesis index (ΣV), were used to investigate specific geochemical signatures of chemosynthesis. Our results show that δ¹⁵N_AA values provide a number of new proxies for relative reliance on chemosynthesis, including TL, ∑V, and both δ¹⁵N values and molar percentages (Gly/Glu mol% index) of specific AA. Together, these parameters suggested that relative chemoautotrophy is linked to both degree of venting from seeps and mussel bed size. Finally, we tested a Bayesian mixing model using diagnostic AA δ¹⁵N values, showing that percent contribution of chemoautotrophic versus heterotrophic production to seep mussel nutrition can be directly estimated from δ¹⁵N_AA values. Our results demonstrate that δ¹⁵N_AA analysis can provide a new set of geochemical tools to better understand mixotrophic ecosystem function and energetics, and suggest extension to the study of ancient chemosynthetic environments in the fossil record.

中文翻译：

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利用化学共生贻贝 (Bathymodiolus childressi) 中的氨基酸 δ15N 研究深海冷泉中资源和能量功能的新地球化学工具

为了重建化石记录中化学合成环境的生态系统结构，必须开发地球化学代理。在这里，我们提出了一套用于追踪化学合成生产的新型化合物特定同位素参数，重点是了解深海冷渗环境中的氮动力学。我们检查了来自 NE 大西洋边缘三个地理上不同渗漏点的化学共生双壳类Bathymodiolus childressi，并将同位素数据与非化学合成沿海贻贝进行比较，以测试水深、渗出活动和/或贻贝床大小是否与化学合成生产的差异有关. 碳 (δ ¹³ C) 和氮 (δ ¹⁵ N) 和 δ ¹⁵的整体同位素分析鳃和肌肉组织中单个氨基酸 (δ ¹⁵ N _AA ) 的N 值，以及 δ ¹⁵ N _AA衍生参数，包括营养水平 (TL)、基线 δ ¹⁵ N 值 (δ ¹⁵ N _Phe ) 和 a微生物再合成指数 (Σ V ) 用于研究化学合成的特定地球化学特征。我们的结果表明，δ ¹⁵ N _AA值为化学合成的相对依赖提供了许多新的代表，包括 TL、∑V 和 δ ¹⁵特定 AA 的 N 值和摩尔百分比（Gly/Glu mol% 指数）。总之，这些参数表明相对化学自养与渗漏的排放程度和贻贝床大小有关。最后，我们使用诊断性 AA δ ¹⁵ N 值测试了贝叶斯混合模型，表明可以从 δ ¹⁵ N _AA值直接估计化学自养与异养生产对渗出贻贝营养的贡献百分比。我们的结果表明，δ ¹⁵ N _AA分析可以提供一套新的地球化学工具，以更好地了解混合营养生态系统功能和能量学，并建议扩展到化石记录中古代化学合成环境的研究。