Collaborative Research: Glacial Lake Ojibway Chronology to Test the 8,200 yr Cold-Event Trigger

我们对导致8200年寒冷事件的气候突变的理解存在根本性的差距。假定的触发因素是融水突然进入高纬度地区，但只有为其他目的进行的初步研究才提供了触发因素及其源区的证据。该项目的目的是确认或修正劳伦斯融水排水事件与8200年冷事件之间的阶段。长期目标是了解冰盖与气候变化之间相互作用的本质。一个核心假设是，奥吉布威冰川湖冰川坝的破裂是一个持续了几个世纪的多步骤过程。这项工作的基本原理是，对冰湖排水进行严格限制的年龄分配，将允许进行更详细的建模实验，或者迫使人们重新考虑融水在这次气候变化中的作用，以及更早的事件，如新仙女木期。对上覆的海洋贝壳进行的有限放射性碳测年目前只能提供一个较年轻的排水年表。该湖相序列的直接和重复定年以及现代相关技术将把最终的排水事件（或事件）置于绝对时间。地层学最年轻的部分目前只在少数几个地方出现，而且描述各不相同。在单一灾难性湖泊排水的模型中，这个序列不应该显示这种变化。通过生成新的合成节律序列并将其与现有序列进行比较，应该可以描述融水排出的性质。古地磁长期变化地层学，结合x射线荧光扫描生成的地球化学数据，将有助于评估节奏岩的年性质和节奏岩厚度相关性。这项工作是原创的，因为它将劳伦泰德冰盖最后阶段的事件置于高分辨率的时间尺度上。预期的结果是通过每年解决的记录来测试8,200年事件的融水触发因素，并对日益增长的时间限制，冰退缩和晚冰期古水文的高分辨率记录进行重要补充。更广泛的影响：奥吉布威湖阀门是一个连接发现和教学的时间序列。数据序列通常用于指导气候变率、光谱分析和地质年代学等主题。这些特殊的记录有助于从入门到研究生水平的这些概念的教学。该奖项通过辛辛那提大学和默西赫斯特学院的本科生和研究生研究项目直接支持感兴趣的学生。在默西赫斯特学院，这些数据通过开发新的实验室项目来加强基础设施，强调通过研究进行教学。这项工作有助于重新引入数据的效用，并为下一代消冰模式建立框架。这一贡献意义重大，因为它为理解劳伦泰德冰盖和北大西洋淡水流量在气候突变中的作用提供了一个新的时间框架。结果将被公布并提交给国家地球物理数据中心，以便世界各地的专家可以随时获得。

There is a fundamental gap in our understanding of the events leading up to the abrupt climate change known as the 8,200 yr cold event. The assumed trigger is the sudden introduction of meltwater into high latitudes, yet only preliminary studies undertaken for other purposes have provided evidence for the trigger and its source area. The objective of this project is to confirm or revise the phasing between Laurentide meltwater drainage events and the 8,200 yr cold event. The long-term goal is to understand the nature of interactions between ice sheets and climate change. It is a central hypothesis is that the break-up of the glacier dam holding in glacial Lake Ojibway was a multi-stepped process operating over centuries. The rationale for this work is that a well-constrained age assignment for the glacial lake drainage will either allow for more detailed modeling experiments or force reconsideration of the role of meltwater in not only this climatic shift, but also earlier events such as the Younger Dryas. Limited radiocarbon dates on overlying marine shells currently provide only a younger bracket on the drainage chronology. Direct and replicated dating of this lacustrine sequence as well as modern correlation techniques will place the final drainage event (or events) into absolute time. The youngest portion of the stratigraphy is currently only represented in a few places, and descriptions vary. In the model of a single catastrophic lake drainage, this sequence should not display this variation. By generating new synthetic rhythmite sequences and comparing them to existing ones, it should be possible to describe the nature of meltwater expulsion. Paleomagnetic secular variation stratigraphy, combined with geochemical data generated via X-ray fluorescence scanning, will help to assess the annual nature of the rhythmites and rhythmite thickness correlations. This work is original because it will place the events of the final stages of the Laurentide Ice Sheet into a high resolution time scale. The expected product is a test of a meltwater trigger of the 8,200 year event via annually resolved records, and a critical addition to a growing body of temporally constrained, high resolution records of ice retreat and late-glacial paleohydrology.Broader Impacts: The Lake Ojibway varves are a time-series that connect discovery and teaching. Data sequences are commonly used to instruct topics such as climate variability, spectral analysis, and geochronology. These particular records aid teaching of these concepts from the introductory to graduate level. This award directly supports interested students via undergraduate and graduate research projects at both the University of Cincinnati and Mercyhurst College. At Mercyhurst College, these data enhance infrastructure via the development of a new laboratory program emphasizing teaching through research. This work helps reintroduce the data's utility and establish a framework for the next generation of deglaciation models. This contribution is significant because it generates a new chronological framework to understand the roles of the Laurentide Ice Sheet and of freshwater flux to the North Atlantic in abrupt climate change. Results will be published and submitted to the National Geophysical Data Center, so that they will be readily available to experts worldwide.