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

SGER：制定蒙大拿州冰川国家公园新冰川作用年表

• 批准号: 0808861
• 负责人: Jeffrey Munroe
• 金额: $ 0.7万
• 依托单位: Middlebury College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-02-01 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0808861&HistoricalAwards=false
• 关键词: SGER; Developing; Chronology; Neoglaciation; Glacier

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.

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一个标志性表现，因为冰川退缩是对气温上升的一种反应，而且国家公园被认为是自然状态下保护地球生态系统的地方。 冰川国家公园中冰川的历史相对知之甚少，从冰河时代结束（大约20,000年前）到小冰河时代，大约在公元1860年结束。 更具体地说，人们对公园的冰川何时形成以及在历史时期之前它们是如何波动的知之甚少。 为了弥补这一缺陷，美国地质调查局在2007年夏天提供了后勤支持，从公园西北角的大型冰川阿加西冰川下方的一个湖泊中提取沉积物岩心。 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。 将对岩心进行有机质、生物硅、矿物磷含量和粒度分布分析。 将采用彩色分光光度法协助确定岩心沉积学的变化。 适合AMS 14 C测年的陆地有机碎片将被清除并储存起来，以供今后分析。 此外，将提交两个表层岩心最上层几分米的样品进行210 Pb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允许阿加西冰川的详细全新世历史的发展。该项目将使用沉积物沉积和冰川行为之间的已知关系，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。 该国家公园冰川的消失在关于气候变化的辩论中引起了广泛的关注，尽管没有研究表明冰川过去的变化可以正确看待最近的融化。 沉积物中的有机质和生物硅含量应该与冰川的范围成反比，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，因为更大的冰川会产生更多含磷的淤泥。 将使用粒度分析来量化沉积物中岩石粉的丰度，作为冰川存在/不存在以及冰川范围的代表。 由此产生的全新世冰川波动的更好的理解也将有助于重建该地区的气候变化在千年，百年和十年的时间尺度。 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，在干旱期间为溪流和湿地提供可靠的水源，并通过其前进和后退驱动干扰和演替模式。