SGER: Developing a Chronology for Neoglaciation in Glacier National Park, Montana

冰川国家公园的冰川正在迅速消退，可能在未来几十年内完全消失。这种情况引起了公众的关注，因为冰川退缩是全球气候变化的标志性表现，因为人们直观地认为冰川退缩是对气温上升的反应，因为国家公园被认为是保护自然状态下地质生态系统的地方。冰川国家公园从冰河时代末期（大约2万年前）到小冰河时代（大约在公元1860年结束）之间的冰川历史，人们所知相对较少。更具体地说，人们对公园的冰川何时形成以及它们在历史时期之前是如何波动的知之甚少。为了纠正这一缺陷，美国地质调查局在2007年夏天为从阿加西冰川（位于公园西北角的一个大冰川）下的一个湖泊中提取沉积物岩心提供了后勤支持。这项探索性研究的小额赠款将为测量从冰川国家公园的一个重要地点提取的湖芯的沉积特性提供支持。将分析岩心的有机质、生物成因二氧化硅、矿物磷含量和粒度分布。彩色分光光度法将用于协助鉴定岩心沉积学的变化。适合AMS 14C测年的陆生有机碎片将被移除并储存以供将来分析。此外，两个表面岩心最上面几分米的样品将被提交进行210Pb测年，以确定过去200年左右的沉积年代。总的来说，这种涉及多种实验室方法和地质年代学工具的多代理方法将使阿加西冰川全新世的详细历史得以发展。该项目将利用已知的沉积物沉积和冰川行为之间的关系，加上精确的测年技术，为冰川国家公园的全新世冰川作用制定详细的年表。在关于气候变化的辩论中，该国家公园冰川的消失引起了广泛的关注，尽管没有研究确定冰川过去的变化日期，以正确看待最近的融化。沉积物的有机质和生物硅含量应该与冰川范围成反比，因为更冷、更浑浊的水会降低湖泊的生产力。相比之下，矿物磷应该与冰川的范围成正比，因为越大的冰川会产生更多含磷的淤泥。粒度分析将用于量化沉积物中岩石粉的丰度，作为冰川存在/不存在和冰川范围的代表。由此产生的对全新世冰川波动的更好理解也将有助于重建该地区在千年、百年和十年时间尺度上的气候变率。该项目还将为国家公园提供生态和管理信息，因为冰川是生态系统的重要组成部分，在干旱时期为溪流和湿地提供可靠的水源，并通过冰川的进退驱动扰动和演替模式。

The glaciers of Glacier National Park are retreating rapidly and may disappear entirely within the next few decades. This situation has galvanized public attention, because glacier retreat provides an iconic manifestation of global climate change, because it is intuitive that glacier retreat is a response to rising temperatures, and because national parks are revered as places where geoecosystems are considered protected in their natural state. Relatively little is known about the history of glaciers in Glacier National Park between the end of the Ice Age (roughly 20,000 years ago) and the Little Ice Age, which ended about AD 1860. more specifically, little is known about when the park's glaciers formed and how they fluctuated before the historic period. To rectify this shortcoming, the U.S. Geological Survey provided logistical support in the summer of 2007 for the retrieval of sediment cores from a lake below Agassiz Glacier, a large glacier in the northwestern corner of the park. This Small Grant for Exploratory Research will provide support to measure sedimentary properties in lake cores already extracted from an important site in Glacier National Park. The cores will be analyzed for organic matter, biogenic silica, mineral phosphorous content, and grain-size distribution. Color spectrophotometry will be applied to assist in identifying changes in core sedimentology. Terrestrial organic fragments suitable for AMS 14C dating will be removed and stored for future analysis. In addition, samples from the uppermost few decimeters of the two surface cores will be submitted for 210Pb dating to develop a chronology for sedimentation during the past 200 years or so. Overall this multi-proxy approach involving multiple lab methods and geochronologic tools will allow development of a detailed Holocene history of the Agassiz Glacier.This project will use known relationships between sediment deposition and glacier behavior, plus refined dating techniques, to develop a detailed chronology for Holocene glaciation in Glacier National Park. The disappearance of glaciers in that national park has drawn much popular attention in debates about climate change, even though no studies have dated past shifts in glacial ice to put the recent melting into perspective. The organic matter and biogenic silica content of the sediment should vary inversely to glacier extent because colder, more turbid water would decrease productivity in the lake. In contrast, mineral phosphorous should be directly proportional to glacier extent because a larger glacier would generate more silt containing phosphorous. Grain-size analysis will be used to quantify the abundance of rock flour in the sediment as a proxy for glacier presence/absence, and for glacier extent. The resulting improved understanding of Holocene glacial fluctuations will also aid efforts to reconstruct climate variability in this region over millennial, centennial, and decadal timescales. This project also will provide ecological and management information for the national park because glaciers are crucial components of the ecosystem, providing reliable sources of water to streams and wetlands during periods of drought, and driving disturbance and succession patterns through their advance and retreat.