Abstract A deep chlorophyll layer (DCL) is a common feature of many deep, oligotrophic lakes including Lake Superior. Mechanisms generating and maintaining DCLs are variable across lakes, and seasonal patterns and relationships of DCL structure to physical variables are not well described. Using vertical profile data for physical and biological variables from western and central Lake Superior, we described seasonal patterns in DCL structure and other physical and biological parameters and applied linear mixed-effects models to determine how different physical factors (surface temperature, thermocline depth, and 1% photosynthetically active radiation (PAR) depth) affect the depth, thickness, maximum concentration, and integrated chlorophyll of the DCL. We observed clear seasonal patterns in the development and degradation of the DCL that coincide with seasonal changes in light and temperature. Modeling analysis using linear mixed-effects models showed that the DCL thickness was best predicted by surface temperature (R2 = 0.51) followed by thermocline depth (R2 = 0.36), and the deep chlorophyll maximum (DCM) concentration was best predicted by surface temperature (R2 = 0.26). The 1% PAR depth was not implicated as an important predictor, but observations from seasonal data suggest that it plays a role in the depth of the DCM. While no relationship was found between surface temperature and DCL-integrated chlorophyll, DCL thickness decreased and DCM concentration increased with increasing surface temperature, which could have implications for productivity in the DCL as the lake continues to warm.

中文翻译：

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苏必利尔湖深叶绿素层的季节性和物理驱动因素，对快速变暖的湖泊有影响

摘要 深叶绿素层 (DCL) 是包括苏必利尔湖在内的许多贫营养深湖的共同特征。不同湖泊产生和维持 DCL 的机制各不相同，而且 DCL 结构与物理变量的季节性模式和关系没有得到很好的描述。使用苏必利尔湖西部和中部的物理和生物变量的垂直剖面数据，我们描述了 DCL 结构和其他物理和生物参数的季节性模式，并应用线性混合效应模型来确定不同的物理因素（地表温度、温跃层深度和1% 光合有效辐射 (PAR) 深度）会影响 DCL 的深度、厚度、最大浓度和综合叶绿素。我们观察到 DCL 发展和退化的明显季节性模式，与光和温度的季节性变化相吻合。使用线性混合效应模型的建模分析表明，DCL 厚度最好由地表温度 (R2 = 0.51) 预测，其次是温跃层深度 (R2 = 0.36)，深部叶绿素最大值 (DCM) 浓度最好由地表温度预测 ( R2 = 0.26）。1% 的 PAR 深度并不作为重要的预测因子，但来自季节性数据的观察表明它在 DCM 的深度中起作用。虽然在地表温度和 DCL 整合的叶绿素之间没有发现任何关系，但随着表面温度的升高，DCL 厚度减小，DCM 浓度增加，随着湖泊继续变暖，这可能对 DCL 的生产力产生影响。