Abstract Geneva Lake in Wisconsin, USA, is > 20,000 years old and contains a 30-m thick lacustrine sediment record of mid-continent North American climate and environmental change. Here we describe a sediment record from Geneva Lake spanning the past 14,500 years. From scanning X-ray fluorescence, organic C and N concentrations and isotopes, X-ray diffraction, magnetic susceptibility, and grain size of bulk sediments, we infer changes in sediment sources over time including: abrupt decline in inputs of remobilized loess ∼13,400 cal yr BP followed by a gradual transition to organic-rich marl deposition by ∼10,400 cal yr BP as the landscape stabilized following a period of permafrost thaw and vegetation development; deposition of a minerogenic unit at ∼8,200 cal yr BP that may record enhanced eolian activity during the widespread “8.2 ka event; ” and elevated zinc, lead, and arsenic from human activities following regional industrialization. Within the Holocene marl, we also use isotopic (δ18O and δ13C) and trace metal ratio (Sr/Ca and Mg/Ca) analyses of ostracode valves paired with concentrations and hydrogen isotopic composition (δ2H) of leaf wax n-alkanes to infer climate and hydrological change. Groundwater had a large but declining influence on lake water chemistry from 11,800 to 9,700 cal yr BP, precluding inferences of regional climate from our lacustrine proxies during this period. δ2H values of terrestrial n-C29 alkanes show little variability from 9,700 to present, indicating the average isotopic composition of local precipitation was relatively stable, reflecting stable condensation temperatures and source. In contrast, a gradual trend towards more δ18O- and δ2H-depleted lake water and lower lake water Sr/Ca from 9700 cal yr BP to present suggest decreasing evaporation of lake water and increasing precipitation amounts throughout the Holocene and resulting shorter lake water residence times. Lake water Mg/Ca variations over the past 9,700 years broadly parallel regional pollen-based reconstructions of summer temperatures. Neither Mg/Ca nor terrestrial leaf wax δ2H suggest long-term directional shifts in temperature at this site through the middle to late Holocene, as climate became wetter. It appears that precipitation isotopes did not track local temperatures on millennial timescales in this part of mid-continent North America through the Holocene, and instead may have covaried with changes in Northern Hemisphere latitudinal temperature gradients driven by large Arctic temperature changes.

中文翻译：

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美国大陆中部的晚冰期和全新世古环境，从日内瓦湖叶蜡、ostracode 瓣和大块沉积物化学推断

摘要 美国威斯康星州的日内瓦湖已有超过 20,000 年的历史，包含北美大陆中部气候和环境变化的 30 米厚湖泊沉积物记录。在这里，我们描述了过去 14,500 年日内瓦湖的沉积物记录。从扫描 X 射线荧光、有机 C 和 N 浓度和同位素、X 射线衍射、磁化率和大块沉积物的粒度，我们推断沉积物来源随时间的变化，包括： 再动员黄土输入量的突然下降 ∼13,400 cal随着多年冻土解冻和植被发育期的景观稳定，随着每年 BP 逐渐过渡到富含有机质泥灰岩沉积约 10,400 cal yr BP；在约 8,200 cal yr BP 处沉积了一个成矿单元，它可能记录了广泛的“8.2 ka 事件”期间风成活动的增强；”以及区域工业化后人类活动中锌、铅和砷的含量升高。在全新世泥灰岩中，我们还使用同位素（δ18O 和 δ13C）和痕量金属比（Sr/Ca 和 Mg/Ca）分析 ostracode 阀，结合叶蜡正烷烃的浓度和氢同位素组成 (δ2H) 来推断气候和水文变化。从 11,800 到 9,700 cal yr BP，地下水对湖水化学的影响很大，但在下降，排除了这一时期我们的湖泊代理对区域气候的推断。陆地 n-C29 烷烃的 δ2H 值从 9,700 到现在几乎没有变化，表明局部降水的平均同位素组成相对稳定，反映了稳定的冷凝温度和来源。相比之下，从 9700 卡年 BP 到现在，越来越多的 δ18O 和 δ2H 耗尽湖水和降低湖水 Sr/Ca 的逐渐趋势表明，整个全新世湖水蒸发减少和降水量增加，从而导致湖水停留时间缩短。过去 9,700 年的湖水 Mg/Ca 变化与基于花粉的夏季温度区域重建大致平行。随着气候变得更湿，Mg/Ca 和陆地叶蜡 δ2H 都表明该地点的温度在全新世中期至晚期发生长期定向变化。在北美大陆中部的这一地区，降水同位素似乎没有在千年时间尺度上追踪到全新世的局部温度，