Abstract Biogeochemical proxy records from Icelandic lake sediment track large-scale shifts in North Atlantic Holocene climate and highlight the impact that North Atlantic Ocean- and atmospheric circulation has on Iceland’s climate and environment. Following Early Holocene warmth, centennial-scale climate change is superimposed on millennial-scale cooling, culminating in the transition to the Little Ice Age (∼1300–1900 CE). Although the long-term cooling trend is presumably driven by variations in Earth’s orbit and the concomitant decline in Northern Hemisphere (NH) summer insolation, the centennial-scale variability has been linked to the strength of the Atlantic Meridional Overturning Circulation (AMOC), volcanism coupled with sea ice/ocean related feedbacks, internal modes of atmospheric variability, and plausibly variations in solar irradiance. One manifestation of these regional climate changes on Iceland is the intensification of soil erosion, resulting in the degradation of ecosystems and landscape. In recent millennia, persistent and severe soil erosion has also been linked to human impact on the environment following the settlement ∼870 CE, rapid population growth, introduction of livestock and the poorly consolidated nature of tephra dominated soils. Lake proxy composite records suggest that although event-dominated landscape instability and soil erosion from the Early to Middle Holocene were likely triggered by large volcanic eruptions, the landscape was capable of recovering. However, a threshold was reached ∼5 ka BP, resulting in a state change whereby the Icelandic landscape could no longer fully recover from cold-events and/or tephra fall. Landscape sensitivity to climate further intensified at ∼1.5 ka BP as identified by regime shift analysis. Hence, widespread and irreversible soil erosion began several centuries before the acknowledged settlement of Iceland, with a second acceleration ∼1250 CE. A 2 ka fully coupled climate transient simulation using CESM1.1 shows a ∼0.5 °C reduction in summer temperature around Iceland in the first millennium CE, consistent with increased landscape instability and soil erosion in Iceland. A second phase of persistent summer cooling in the model occurs after 1150 CE, with stronger cooling after 1450 CE, reaching a maximum shortly after 1850 CE, ∼1 °C lower than at the start of the simulation. Our results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact, with intensification of these processes following settlement particularly during the cooling associated with the Little Ice Age. Given that the conclusions drawn in this review diverge from the standard paradigm of human-induced soil erosion history in Iceland, research should continue to focus on this complex question from multiple disciplines. In particular, a combination of emerging biogeochemical techniques (e.g. lipid biomarkers and ancient DNA) may be best poised to test and quantify the relative roles of natural environmental variables and human settlement in the history of soil erosion on Iceland.

中文翻译：

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冰岛景观不稳定的全新世历史：我们能否解卷积气候、火山活动和人类活动的影响？

摘要 冰岛湖泊沉积物的生物地球化学代理记录追踪了北大西洋全新世气候的大规模变化，并突出了北大西洋和大气环流对冰岛气候和环境的影响。在全新世早期变暖之后，百年尺度的气候变化叠加在千年尺度的降温上，最终过渡到小冰河时代（约公元 1300-1900 年）。虽然长期降温趋势可能是由地球轨道的变化和北半球 (NH) 夏季日照随之下降所驱动的，但百年尺度的变化与大西洋经向翻转环流 (AMOC)、火山活动的强度有关再加上海冰/海洋相关的反馈、大气变化的内部模式以及太阳辐照度的可能变化。冰岛这些区域性气候变化的表现之一是土壤侵蚀加剧，导致生态系统和景观退化。在最近的几千年里，持续和严重的土壤侵蚀也与人类在公元 870 年定居后对环境的影响、人口快速增长、牲畜的引入以及以火山灰为主的土壤的固结性差有关。湖泊替代综合记录表明，尽管从全新世早期到中期，事件主导的景观不稳定和土壤侵蚀很可能是由大型火山喷发引发的，但景观能够恢复。然而，达到了约 5 ka BP 的阈值，导致冰岛景观无法再从寒冷事件和/或火山灰坠落中完全恢复的状态变化。通过制度转移分析确定，景观对气候的敏感性在~1.5 ka BP 处进一步加强。因此，在公认的冰岛定居之前几个世纪，广泛且不可逆的土壤侵蚀就开始了，第二次加速约为公元 1250 年。使用 CESM1.1 进行的 2 ka 完全耦合气候瞬态模拟显示，在公元第一个千年，冰岛周围的夏季温度降低了约 0.5 °C，这与冰岛的景观不稳定性和土壤侵蚀增加相一致。模型中持续夏季降温的第二阶段发生在公元 1150 年之后，公元 1450 年之后降温更强，在公元 1850 年之后不久达到最大值，比模拟开始时低约 1°C。我们的研究结果表明，区域气候和火山活动的自然变化可能是人类影响之前土壤侵蚀的原因，随着沉降后这些过程的加剧，特别是在与小冰河时代相关的冷却过程中。鉴于本综述得出的结论与冰岛人为土壤侵蚀历史的标准范式不同，研究应继续关注来自多个学科的这个复杂问题。特别是，新兴生物地球化学技术（例如脂质生物标志物和古代 DNA）的组合可能最适合测试和量化自然环境变量和人类定居在冰岛土壤侵蚀历史中的相对作用。研究应该继续关注这个来自多个学科的复杂问题。特别是，新兴生物地球化学技术（例如脂质生物标志物和古 DNA）的组合可能最适合测试和量化冰岛土壤侵蚀历史中自然环境变量和人类定居点的相对作用。研究应该继续关注这个来自多个学科的复杂问题。特别是，新兴生物地球化学技术（例如脂质生物标志物和古代 DNA）的组合可能最适合测试和量化自然环境变量和人类定居在冰岛土壤侵蚀历史中的相对作用。