(Table S1) Radiocarbon dates of organic matter from Lena Delta ice wedges@en

Relative to the past 2,000 years, the Arctic region has warmed significantly over the past few decades. However, the evolution of Arctic temperatures during the rest of the Holocene is less clear. Proxy reconstructions, suggest a long-term cooling trend throughout the mid- to late Holocene, whereas climate model simulations show only minor changes or even warming. Here we present a record of the oxygen isotope composition of permafrost ice wedges from the Lena River Delta in the Siberian Arctic. The isotope values, which reflect winter season temperatures, became progressively more enriched over the past 7,000 years, reaching unprecedented levels in the past five decades. This warming trend during the mid- to late Holocene is in opposition to the cooling seen in other proxy records. However, most of these existing proxy records are biased towards summer temperatures. We argue that the opposing trends are related to the seasonally different orbital forcing over this interval. Furthermore, our reconstructed trend as well as the recent maximum are consistent with the greenhouse gas forcing and climate model simulations, thus reconciling differing estimates of Arctic and northern high-latitude temperature evolution during the Holocene.相较于过去两千年的背景，北极地区在近数十年间出现了显著增温。然而，全新世（Holocene）其余时段的北极温度演化过程仍不甚明晰。代用指标重建（proxy reconstructions）结果显示，全新世中晚期存在长期降温趋势，而气候模式模拟结果仅呈现微弱变化，甚至表现为增温。本研究提供了取自北极西伯利亚勒拿河三角洲的多年冻土（permafrost）冰楔（ice wedges）的氧同位素组成记录。这些可反映冬季气温的同位素数值在过去7000年间逐渐富集，并在近50年达到前所未有的水平。这一全新世中晚期的增温趋势与其他代用指标记录所揭示的降温趋势相悖。然而，多数现有代用指标记录均偏向于反映夏季气温。我们认为，这种趋势相悖的现象与该时段内季节差异显著的轨道强迫（orbital forcing）有关。此外，我们重建的温度变化趋势以及近期的气温峰值均与温室气体强迫（greenhouse gas forcing）及气候模式模拟结果相符，从而调和了全新世北极及北部高纬度地区温度演化的不同估算结果。