NOAA/WDS Paleoclimatology - Arrowhead Lake, Greenland, XRF, Magnetic Susceptibility and d18O Data Over the Past 8300 Years

Holocene paleotemperature records from ice-free margins of Greenland suggest spatiotemporal heterogeneity in the timing of key climate transitions following retreat of the Greenland Ice Sheet. However, the paucity of high-resolution climate records from this region limits our understanding of the timing, spatial variation, and drivers of Holocene climate variability. Here, we present a middle to late Holocene climate reconstruction based on δ18O of aquatic invertebrate (chironomid and cladoceran) remains and sediment geochemistry from lake sediments to elucidate millennial to submillennial-scale drivers of climate in southwestern Greenland. We establish that our site, Arrowhead Lake, is a through-flowing basin with an integrated signal of annual meteoric water with no evidence of significant evaporative enrichment. Core sediment geochemistry captures the transition from minerogenic-dominated to organic-rich sediments ~8 cal ka BP. Chitin-based δ18O measurements of both chironomid head capsules and ephippia exhibit similar temporal variability through the record, broadly decreasing from 8.2 cal ka BP to present, concurrent with decreasing summer insolation and regional Neoglacial cooling. A simplified assumption that temperature is the sole driver of changes in isotopes of precipitation yields an estimated average temperature change from the middle to late Holocene at Arrowhead Lake of 2.1–3.0 °C, comparable to existing estimates of middle to late Holocene temperature decline in western Greenland. Depleted δ18O values after 3.3 cal ka BP correspond to the onset of Neoglacial cooling and independent evidence for a slowdown of the West Greenland Current, and suggests that both temperature and sea-ice variability were important controls on isotopic variability at this site. Highly depleted isotopic values at 8.2 cal ka BP followed by high isotopic variability in the early part of the middle Holocene suggests that our record may capture regional 8.2 ka cooling. This new isotope record provides insight into climate influences during the middle and late Holocene along the western Greenland margin that are important for understanding how ongoing melt of the Greenland Ice Sheet and amplified warming in the Arctic may impact the climate system.

来自格陵兰无冰边缘的全新世（Holocene）古温度记录显示，格陵兰冰盖（Greenland Ice Sheet）退缩后关键气候转型的发生时间存在时空异质性。然而，该区域高分辨率气候记录的匮乏，限制了我们对全新世气候变率的发生时间、空间差异及驱动机制的认知。本研究基于湖泊沉积物中水生无脊椎动物（aquatic invertebrate）摇蚊（chironomid）和枝角类（cladoceran）残骸的δ18O值以及沉积物地球化学数据，重建了格陵兰西南部全新世中晚期的气候序列，以阐明千年至亚千年尺度的气候驱动因子。我们证实，研究点位箭湖（Arrowhead Lake）是一个通流盆地，其沉积物记录整合了年度大气降水信号，未出现显著蒸发富集的迹象。岩心沉积物地球化学记录捕捉到了约8 cal ka BP时从陆源碎屑主导型向富有机质沉积物的转变过程。对摇蚊头囊和卵鞍（ephibia）的基于甲壳素的δ18O测量结果显示，整个记录序列具有相似的时间变异性：整体上从8.2 cal ka BP至今呈下降趋势，与夏季日照辐射减弱及区域新冰期（Neoglacial）降温同步发生。若简化假设温度是降水同位素变化的唯一驱动因子，则可估算出箭湖全新世中晚期的平均温度变化幅度为2.1–3.0 °C，这与格陵兰西部全新世中晚期温度下降的已有估算结果相当。3.3 cal ka BP之后的贫化δ18O值对应新冰期降温的起始，同时与西格陵兰洋流（West Greenland Current）减速的独立证据相吻合，这表明温度与海冰变化均是该点位同位素变异性的重要控制因素。8.2 cal ka BP时出现的高度贫化同位素值，以及随后全新世中期早期的高同位素变异性，暗示本记录可能捕捉到了区域8.2 ka降温事件。这一新的同位素记录为理解格陵兰西部边缘全新世中晚期的气候影响提供了新视角，这对于认识格陵兰冰盖持续消融以及北极放大增暖（Arctic amplified warming）可能如何影响气候系统具有重要意义。