Understanding Holocene climate variability is crucial for predicting future climate change, which will disproportionally affect high-latitude regions. Summer temperature (T) reconstructions in regions such as northern Finland are mainly derived from microfossil data. We reconstructed T spanning the interval 10-1 cal ka BP using branched glycerol dialkyl glycerol tetraethers (brGDGTs) from lake-sediment record from Lake Annan Juomusjärvi (AJU) in northern Finland. The reconstruction shows cool early Holocene conditions, ∼2 °C below the long-term mean (defined by the last 8.5 kyr), followed by persistent warming to a thermal maximum around ∼7.0 cal ka BP, a relatively stable climate (∼0.5 °C above the long-term mean) from 7.0 to 3.5 cal ka BP, and then a long-term cooling trend (−0.1 °C·kyr) since 3.5 cal ka BP. This temperature history is remarkably well replicated by the nearby pollen-T reconstruction from Lake Loitsana. However, Lake Loitsana chironomid and macrofossil data argue for a much earlier thermal maximum at ∼10 cal ka BP. Comparison of chironomid versus pollen records from across northern Fennoscandia confirms this inter-proxy discrepancy on the timing of Holocene peak warmth is a regional-scale phenomenon. Previous studies had raised the possibility that non-climatic noise in certain pollen records, due to local-scale overrepresentation of certain pollen types in the early and mid Holocene, may be contributing to an artificial lag in the thermal maximum. However, brGDGTs are unaffected by terrestrial flora and corroborate a mid-Holocene thermal maximum, which challenges the notion that pollen records are generally prone to misrepresenting the early to mid-Holocene climate history. Alternatively, proxy-specific environmental or mean seasonality biases may explain inter-proxy discrepancies in the timing of peak warmth. Continued diversification of the proxy network will help to better understand inter-proxy differences and refine knowledge of Holocene climate in northern Fennoscandia.

中文翻译：

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使用 brGDGT 重建暖季温度并评估芬诺斯坎迪亚北部全新世温度记录的偏差

了解全新世气候变化对于预测未来气候变化至关重要，未来气候变化将对高纬度地区产生不成比例的影响。芬兰北部等地区的夏季温度（T）重建主要来自微化石数据。我们使用芬兰北部安南 Juomusjärvi 湖 (AJU) 的湖泊沉积物记录中的支链甘油二烷基甘油四醚 (brGDGT) 重建了跨度为 10-1 cal ka BP 的 T。重建显示了全新世早期的凉爽条件，比长期平均值（由最后 8.5 kyr 定义）低约 2 °C，随后持续升温至约 7.0 cal ka BP 左右的最高热值，气候相对稳定（约 0.5 °C） C高于长期平均值）从7.0到3.5 cal ka BP，然后从3.5 cal ka BP开始出现长期降温趋势（-0.1 °C·kyr）。附近 Loitsana 湖的花粉 T 重建很好地复制了这一温度历史。然而，洛伊萨纳湖摇蚊和大型化石数据表明，最热时期的温度要早得多，约为 10 cal ka BP。对芬诺斯坎迪亚北部摇蚊记录与花粉记录的比较证实，全新世峰值温暖时间的代理间差异是一种区域性现象。先前的研究提出了一种可能性，即某些花粉记录中的非气候噪音，由于全新世早期和中期某些花粉类型在局部范围内的代表性过高，可能会导致热最大值的人为滞后。然而，brGDGT 不受陆地植物区系的影响，并证实了全新世中期的最高热，这挑战了花粉记录通常容易歪曲全新世早期至中期气候历史的观点。或者，特定代理的环境或平均季节性偏差可以解释代理之间在峰值温暖时间上的差异。代理网络的持续多样化将有助于更好地了解代理之间的差异并完善对芬诺斯坎迪亚北部全新世气候的了解。