We examined diatom assemblages in a sediment core from Lake Superior (Canada/USA) that spans the interval ~ 500–1350 CE and includes the Medieval Climate Anomaly (MCA), 950–1250 CE. We sought to determine whether diatom assemblages responded to climate change during that warm, dry period. From 500 to 1350 CE, diatom assemblages were dominated by Lindavia ocellata and Lindavia comensis and there were no significant changes in the diatom community during the MCA. In another core from Lake Superior, which spans the period ~ 1815–2010 CE, we documented significant changes in diatom assemblages, which began ca. 1940. We used recently established relationships between planktonic diatom taxa and climate and lake physicochemical variables from monitoring data, to assess the drivers of change in diatom assemblages during the past century. Results from the two cores suggest that multiple environmental drivers, including both climate change and human-mediated influences on nutrient cycling, led to shifts in recent diatom communities in Lake Superior. The lack of change in diatom assemblages during the MCA supports the conclusion that environmental changes in Lake Superior during the past century are novel and were driven largely by human activities.

中文翻译：

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中世纪气候异常和 20 世纪湖上沉积硅藻剖面表明最近的组合变化反映了新的环境条件

我们检查了苏必利尔湖（加拿大/美国）沉积物核心中的硅藻组合，该沉积物核心跨越约 500-1350 CE 的时间间隔，包括中世纪气候异常 (MCA)，950-1250 CE。我们试图确定在那个温暖干燥的时期硅藻组合是否对气候变化做出了反应。从公元 500 年到 1350 年，硅藻组合以 Lindavia ocellata 和 Lindavia comensis 为主，在 MCA 期间硅藻群落没有显着变化。在苏必利尔湖的另一个岩芯中，它跨越了大约公元 1815 年至 2010 年的时期，我们记录了硅藻组合的重大变化，该变化始于约 1940. 我们使用最近建立的浮游硅藻类群与来自监测数据的气候和湖泊物理化学变量之间的关系来评估上个世纪硅藻组合变化的驱动因素。两个核心的结果表明，多种环境驱动因素，包括气候变化和人类对养分循环的影响，导致了苏必利尔湖近期硅藻群落的变化。在 MCA 期间，硅藻组合没有发生变化，这支持了以下结论：过去一个世纪苏必利尔湖的环境变化是新奇的，主要是由人类活动驱动的。