Sometime during the middle to late Holocene (8.2 ka to ∼ 1850–1900 CE), the Greenland Ice Sheet (GrIS) was smaller than its current configuration. Determining the exact dimensions of the Holocene ice-sheet minimum and the duration that the ice margin rested inboard of its current position remains challenging. Contemporary retreat of the GrIS from its historical maximum extent in southwestern Greenland is exposing a landscape that holds clues regarding the configuration and timing of past ice-sheet minima. To quantify the duration of the time the GrIS margin was near its modern extent we develop a new technique for Greenland that utilizes in situ cosmogenic ¹⁰Be–¹⁴C–²⁶Al in bedrock samples that have become ice-free only in the last few decades due to the retreating ice-sheet margin at Kangiata Nunaata Sermia (n=12 sites, 36 measurements; KNS), southwest Greenland. To maximize the utility of this approach, we refine the deglaciation history of the region with stand-alone ¹⁰Be measurements (n=49) and traditional ¹⁴C ages from sedimentary deposits contained in proglacial–threshold lakes. We combine our reconstructed ice-margin history in the KNS region with additional geologic records from southwestern Greenland and recent model simulations of GrIS change to constrain the timing of the GrIS minimum in southwest Greenland and the magnitude of Holocene inland GrIS retreat, as well as to explore the regional climate history influencing Holocene ice-sheet behavior. Our ¹⁰Be–¹⁴C–²⁶Al measurements reveal that (1) KNS retreated behind its modern margin just before 10 ka, but it likely stabilized near the present GrIS margin for several thousand years before retreating farther inland, and (2) pre-Holocene ¹⁰Be detected in several of our sample sites is most easily explained by several thousand years of surface exposure during the last interglaciation. Moreover, our new results indicate that the minimum extent of the GrIS likely occurred after ∼5 ka, and the GrIS margin may have approached its eventual historical maximum extent as early as ∼2 ka. Recent simulations of GrIS change are able to match the geologic record of ice-sheet change in regions dominated by surface mass balance, but they produce a poorer model–data fit in areas influenced by oceanic and dynamic processes. Simulations that achieve the best model–data fit suggest that inland retreat of the ice margin driven by early to middle Holocene warmth may have been mitigated by increased precipitation. Triple ¹⁰Be–¹⁴C–²⁶Al measurements in recently deglaciated bedrock provide a new tool to help decipher the duration of smaller-than-present ice over multiple timescales. Modern retreat of the GrIS margin in southwest Greenland is revealing a bedrock landscape that was also exposed during the migration of the GrIS margin towards its Holocene minimum extent, but it has yet to tap into a landscape that remained ice-covered throughout the entire Holocene.

中文翻译：

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从最近冰期基岩中获取的原地宇宙成因¹⁰ Be– ¹⁴ C– ²⁶ Al测量值，作为一种新的工具来解释格陵兰冰盖尺寸的变化

有时中间晚全新世（8.2期间 か到〜  1850-1900 CE），格陵兰冰盖（格里斯）比其当前配置小。确定全新世冰盖最小值的确切尺寸以及冰缘停留在其当前位置内侧的持续时间仍然具有挑战性。在格陵兰西南部，GrIS在历史上最大程度上的当代退缩正暴露出一种景观，该景观为过去冰盖极小构造和时间安排提供了线索。为了量化GrIS余量接近现代范围的持续时间，我们为格陵兰岛开发了一种新技术，该技术利用原位宇宙成因¹⁰ Be – ¹⁴ C – ²⁶ Al由于格陵兰西南部的Kangiata Nunaata Sermia（n = 12个站点，共36个测量； KNS），由于冰盖边缘的退缩，仅在过去的几十年中才变为无冰的基岩样品中。为了最大程度地利用这种方法，我们使用独立的¹⁰ Be测量（n = 49）和传统的¹⁴ C来细化该地区的冰消历史冰川期的湖泊中所含沉积物的年龄。我们将重建后的KNS地区冰边界历史与格陵兰西南部的其他地质记录以及最近的GrIS变化模拟模拟相结合，以限制格陵兰西南部GrIS最小值的时间和全新世内陆GrIS撤退的幅度，以及探索影响全新世冰盖行为的区域气候历史。我们对 ¹⁰ Be – ¹⁴ C – ²⁶ Al的测量结果表明：（1）KNS在10 ka之前退缩到其现代边界之后 ，但它可能在目前的GrIS边界附近稳定了几千年，之后又退回到更远的内陆。全新世¹⁰是我们的一些样本点的检测是最容易被几千年的表面接触的最后一个间冰期期间解释。此外，我们的新结果表明，GRIS最低程度之后可能发生〜5 万年，和GRIS利润率可能已接近其最终的历史最大程度早 〜2 万年。最近对GrIS变化的模拟能够与表面质量平衡占主导的地区冰盖变化的地质记录相匹配，但是它们产生的模型数据较差，无法适应受海洋和动态过程影响的区域。模拟实现最佳的模型数据拟合表明，由全新世早期至中期温暖带动的冰缘内陆内陷可能已被降水增加所缓解。最近冰化的基岩中的三重 ¹⁰ Be – ¹⁴ C – ²⁶ Al测量值提供了一种新工具，可帮助破译多个时间尺度上比现在小的冰的持续时间。格陵兰西南部GrIS边缘的现代撤退揭示了基岩景观，在GrIS边缘向全新世最小程度迁移的过程中也暴露了基岩景观，但尚未挖掘整个全新世仍被冰覆盖的景观。