Abstract Stable isotope analyses of ostracod shells are a commonly-used proxy for palaeoenvironmental reconstruction. Although the fundamental controls on isotope composition of ostracod shells are well understood and, in some instances, quantifiable, the paleoclimatic and palaeoenvironmental interpretation of records from lake sediments depends strongly on the characteristics of individual lakes including the climatic setting, depth, volume, hydrology, aquatic vegetation and catchment properties. This is particularly important for coastal lakes where physio-chemical variations may occur on diurnal timescales. Here, we combine variations in δ18Owater, δ18Oostracod and δ13Costracod, hourly water temperature, and Mg/Caostracod inferred water temperatures (constraining calcification temperature) to improve palaeoenvironmental interpretation and provide insights into lake carbon cycle. The dataset improves understanding of complex coastal lake site systematics and downcore interpretation of stable isotopes from C. torosa, a geographically widespread brackish water ostracod. The δ18Oostracod values show a complex relationship with temperature and suggest, in most circumstances, that δ18Owater is the dominant control on δ18Oostracod. During times of fresher water, δ13Costracod increases, suggesting increasing aquatic productivity. Above a certain δ18Owater threshold however, aquatic productivity begins to decline. The interpretation of δ13Costracod in some coastal lakes, may therefore be dependent on understanding of the range of expected δ18Owater. Due to short-term (diurnal to seasonal) variations that cause large ranges in δ18Owater and δ18Oostracod, stable isotope analyses of C. torosa should be: (1) undertaken on multiple single shells (2) where carapaces are preserved, paired with trace-element/Ca analyses on the same individual; and (3) undertaken alongside a study of the modern lake system.

中文翻译：

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沿海湖泊鲢鱼的 δ18O 和 δ13C：现代系统学和岩下解释

摘要 介形虫壳的稳定同位素分析是古环境重建的常用代理。尽管对介形虫壳同位素组成的基本控制已得到充分理解，并且在某些情况下是可量化的，但对湖泊沉积物记录的古气候和古环境解释在很大程度上取决于各个湖泊的特征，包括气候环境、深度、体积、水文、水生植被和集水区特性。这对于沿海湖泊尤其重要，因为那里的物理化学变化可能会在昼夜尺度上发生。在这里，我们结合了 δ18Owater、δ18Oostracod 和 δ13Costracod 的变化，每小时水温，和 Mg/Caostracod 推断水温（限制钙化温度）以改善古环境解释并提供对湖泊碳循环的见解。该数据集提高了对复杂的沿海湖泊站点系统学的理解和对 C. torosa 稳定同位素的下行解释，这是一种地理上广泛存在的咸水介形虫。δ18Oostracod 值显示出与温度的复杂关系，表明在大多数情况下，δ18Owater 是 δ18Oostracod 的主要控制因素。在淡水时期，δ13Costracod 增加，表明水生生产力增加。然而，高于某个 δ18Owater 阈值，水生生产力开始下降。因此，对某些沿海湖泊中 δ13Costracod 的解释可能取决于对预期 δ18Owater 范围的了解。由于短期（昼夜到季节性）变化导致 δ18Owater 和 δ18Oostracod 的大范围变化，C. torosa 的稳定同位素分析应：(1) 在保留甲壳的多个单壳上进行 (2) 与微量-对同一个人进行元素/Ca 分析；(3) 与现代湖泊系统的研究同时进行。