NOAA/WDS Paleoclimatology - Upper Grindelwald Glacier Holocene Fluctuation Reconstruction

Mountain glaciers and their sediments are prominent witnesses of climate change, responding sensitively to even small modifications in meteorological parameters. Even in such a classical and thoroughly studied area as the European Alps the record of Holocene glacier mass-balance is only incompletely known. Here we explore a novel and continuous archive of glacier fluctuations in a cave system adjacent to the Upper Grindelwald Glacier in the Swiss Alps. Milchbach cave became partly ice-free only recently and hosts Holocene speleothems. Four coeval stalagmites show consistent petrographic and stable isotopic changes between 9.2 and 2.0 ka which can be tied to abrupt modifications in the cave environment as a result of the closing and opening of multiple cave entrances by the waxing and waning of the nearby glacier. During periods of Holocene glacier advances, columnar calcite fabric is characterized by d18O values of about -8.0‰ indicative of speleothem growth under quasi-equilibrium conditions, i.e. little affected by kinetic effect related to forced degassing or biological processes. In contrast, fabrics formed during periods of glacier minima are typical of bacterially mediated calcite precipitation within caves overlain by an alpine soil cover. Moreover, d18O values of the bacterially mediated calcite fabrics are consistent with a ventilated cave system fostering kinetic fractionation. These data suggest that glacier retreats occurred repeatedly before 5.8 ka, and that the amplitudes of glacier retreats became substantially smaller afterwards. Our reconstruction of the Upper Grindelwald Glacier fluctuations agrees well with paleoglaciological studies from other sites in the Alps and provides a higher temporal resolution compared to traditional analyses of peat and wood remains found in glacier forefields.

山地冰川及其沉积物是气候变化的重要佐证，即便气象参数发生微小变化，它们也会做出灵敏响应。即便在欧洲阿尔卑斯山这类经典且已被深入研究的区域，全新世（Holocene）冰川物质平衡的完整记录仍未被完全揭示。本研究针对瑞士阿尔卑斯山格林德瓦尔德上冰川（Upper Grindelwald Glacier）附近的洞穴系统展开探索，旨在获取一套全新且连续的冰川波动记录档案。米尔赫巴赫洞穴（Milchbach Cave）直至近期才部分脱离冰盖覆盖，洞内保存有全新世洞穴次生化学沉积物（speleothems）。4件同期形成的石笋（stalagmites）呈现出9.2~2.0 ka期间一致的岩相学与稳定同位素变化特征，这些变化可归因于附近冰川的进退导致多个洞穴入口被封闭或开启，进而引发洞穴环境的突变。在全新世冰川前进时期，柱状方解石组构的δ¹⁸O值约为-8.0‰，这表明洞穴次生化学沉积物形成于准平衡条件下，几乎不受强制脱气或生物过程相关的动力学效应影响。与之相反，冰川规模极小期形成的组构，则以洞穴覆有高山土壤层时细菌介导的方解石沉淀为典型特征。此外，细菌介导方解石组构的δ¹⁸O值，与通风良好的洞穴系统促进动力学分馏的特征相契合。这些数据表明，5.8 ka之前曾多次发生冰川退缩事件，且此后冰川退缩的幅度显著收窄。本研究重建的格林德瓦尔德上冰川波动历史，与阿尔卑斯山其他点位的古冰川学（paleoglaciological）研究结果高度吻合；相较于冰川前缘传统的泥炭与木质残体分析方法，本研究的时间分辨率更高。