Department of Geology, University of Vermont, Burlington, VT 05405;
Gund Institute for Environment, University of Vermont, Burlington, VT 05405.
Proc Natl Acad Sci U S A. 2021 Mar 30;118(13). doi: 10.1073/pnas.2021442118.
Understanding the history of the Greenland Ice Sheet (GrIS) is critical for determining its sensitivity to warming and contribution to sea level; however, that history is poorly known before the last interglacial. Most knowledge comes from interpretation of marine sediment, an indirect record of past ice-sheet extent and behavior. Subglacial sediment and rock, retrieved at the base of ice cores, provide terrestrial evidence for GrIS behavior during the Pleistocene. Here, we use multiple methods to determine GrIS history from subglacial sediment at the base of the Camp Century ice core collected in 1966. This material contains a stratigraphic record of glaciation and vegetation in northwestern Greenland spanning the Pleistocene. Enriched stable isotopes of pore-ice suggest precipitation at lower elevations implying ice-sheet absence. Plant macrofossils and biomarkers in the sediment indicate that paleo-ecosystems from previous interglacial periods are preserved beneath the GrIS. Cosmogenic Al/Be and luminescence data bracket the burial of the lower-most sediment between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma. In the upper-most sediment, cosmogenic Al/Be data require exposure within the last 1.0 ± 0.1 My. The unique subglacial sedimentary record from Camp Century documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation. The lower sediment derives from an Early Pleistocene GrIS advance. Al/Be ratios in the upper-most sediment match those in subglacial bedrock from central Greenland, suggesting similar ice-cover histories across the GrIS. We conclude that the GrIS persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma.
了解格陵兰冰原（GrIS）的历史对于确定其对变暖的敏感性和对海平面的贡献至关重要；然而，在上一个间冰期之前，其历史知之甚少。大多数知识来自海洋沉积物的解释，这是过去冰原范围和行为的间接记录。在冰芯底部采集的冰下沉积物和岩石为格陵兰冰原在更新世期间的行为提供了陆地证据。在这里，我们使用多种方法从 1966 年收集的 Camp Century 冰芯底部的冰下沉积物中确定格陵兰冰原的历史。这些物质包含了跨越更新世时期的格陵兰西北部冰川作用和植被的地层记录。富含冰孔隙的稳定同位素表明降水发生在较低海拔，暗示冰原不存在。沉积物中的植物大化石和生物标志物表明，以前间冰期的古生态系统保存在格陵兰冰原之下。宇宙成因 Al/Be 和发光数据将最底层沉积物的埋藏时间限定在<3.2±0.4Ma 和>0.7 至 1.4Ma 之间。在上部沉积物中，宇宙成因 Al/Be 数据要求在最近 1.0±0.1Ma 内暴露。来自 Camp Century 的独特的冰下沉积记录记录了至少两次无冰、植被覆盖的时期，每次之后都有冰川作用。下部沉积物来源于早更新世格陵兰冰原的推进。最上层沉积物中的 Al/Be 比值与格陵兰中部冰下基岩的比值相匹配，表明格陵兰冰原的冰盖历史相似。我们得出结论，格陵兰冰原在更新世的大部分时间里都存在，但至少在 110 万年前已经融化并重新形成。
