Tetraether lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), are an increasingly used proxy for reconstructing paleoclimatic and paleoenvironmental dynamics. On a global scale, environmental drivers controlling the distribution of GDGTs in lake systems have been described extensively. However, the drivers that control down-core sedimentary GDGT composition within single lake systems are still poorly constrained. Here, we analysed GDGTs in a sediment core collected from Lake Höglwörth (Bavaria, Germany) covering the last ∼1100 years. The increase in ratio ΣIIIa/ΣIIa values (a ratio which captures the variation of 3 structural isomers of penta- and hexamethylated brGDGTs respectively) reflects a higher contribution of branched (br) GDGTs from aquatic sources after 1800 CE. This is synchronous with a high nutrient input as a result of increased local anthropogenic activities. The climate proxy methylation of branched tetraethers (MBT'_5ME) reveals a pattern that deviates from the anticipated temperature changes during the last millennium. Instead, high MBT'_5ME values from ∼880 to 1120 CE coincide with a period of increased soil input, resulting from lake damming and/or construction of the Höglwörth monastery. Decreased values after 1800 CE until present date correspond to a higher contribution of aquatic brGDGTs, with changes in the dependency between Ia and IIa suggesting a direct influence of bacterial community changes on the MBT'_5ME. The proxy cyclisation of branched tetraethers (CBT') shows a linear increase with time, and a stepwise increase at 1700 CE, when a creek stream inflow channel was rerouted. Over time, MBT’_5ME decreases gradually, while CBT’ and ΣIIIa/ΣIIa increase. This is hypothesized to be potentially caused by decreasing water depth over time and/or post- or syn-sedimentary production of GDGTs. The degree of cyclization (DC') shows variations on shorter timescales, possibly driven by the lake mixing regime and water column redox conditions. Our results indicate that caution must be taken when interpreting GDGTs for paleoclimate and paleoenvironmental reconstruction considering the possible influence of shifts in the provenance of brGDGTs. Further studies focusing on both sedimentary and intact polar lipids are highly recommended to constrain the source (water column, or sedimentary production) of GDGTs in lake sediments.

四醚脂质，例如甘油二烷基甘油四醚（GDGT），越来越多地用于重建古气候和古环境动力学。在全球范围内，控制湖泊系统中 GDGT 分布的环境驱动因素已被广泛描述。然而，控制单湖系统内岩心沉积 GDGT 组成的驱动因素仍然缺乏约束。在这里，我们分析了过去约 1100 年从 Höglwörth 湖（德国巴伐利亚）收集的沉积物岩心中的 GDGT。ΣIIIa/ΣIIa 比率值的增加（该比率分别反映了五甲基化和六甲基化 brGDGT 的 3 种结构异构体的变化）反映了公元 1800 年之后来自水生来源的支链 (br) GDGT 的更高贡献。这与当地人类活动增加导致的高营养输入同步。支化四醚的气候代理甲基化（MBT' _5ME）揭示了一种偏离上个千年期间预期温度变化的模式。相反，公元 880 年至 1120 年的高 MBT' _5ME值与因湖泊筑坝和/或 Höglwörth 修道院建设而导致的土壤输入增加的时期相一致。公元 1800 年之后至今数值下降对应于水生 brGDGT 的较高贡献，Ia 和 IIa 之间依赖性的变化表明细菌群落变化对 MBT' 5ME 的直接_影响。支化四醚 (CBT') 的代理环化显示出随时间线性增加，并在公元 1700 年当溪流流入通道改道时逐步增加。随着时间的推移，MBT' _5ME逐渐减少，而 CBT' 和 ΣIIIa/ΣIIa 逐渐增加。据推测，这可能是由于水深随着时间的推移而减少和/或 GDGT 的后沉积或同沉积生产造成的。环化程度（DC'）显示出较短时间尺度的变化，可能是由湖泊混合机制和水柱氧化还原条件驱动的。我们的结果表明，考虑到 brGDGT 来源变化可能产生的影响，在解释古气候和古环境重建的 GDGT 时必须谨慎。强烈建议进一步研究沉积物和完整的极性脂质，以限制湖泊沉积物中 GDGT 的来源（水柱或沉积产物）。