Doctoral Dissertation Research: Determining the Phasing of Southern Laurentide Ice-Sheet Retreat and Deglacial Climate Forcings using Cosmogenic Radionuclide Dating

博士论文研究：利用宇宙放射性核素测年确定南劳伦太冰盖后退和冰消气候强迫的阶段

• 批准号: 1102801
• 负责人: Anders Carlson
• 金额: $ 1.2万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2014-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1102801&HistoricalAwards=false
• 关键词: Doctoral; Dissertation; Research; Determining; Phasing

This study will improve the retreat chronology of the southern Laurentide Ice Sheet (LIS) in Wisconsin by measuring in-situ cosmogenic nuclides on glacially deposited boulders from terminal and recessional ice marginal deposits. Sample locations will span a range of climate settings and glacial bed conditions. The proposed research will address two hypotheses. (1) Initial ice margin retreat in Wisconsin was synchronous with the rest of the southern LIS. (2) Increasing boreal summer insolation forced LIS deglaciation. Determining the phasing of ice-sheet retreat relative to changes in insolation, atmospheric greenhouse gases, and global climate is important to understanding the mechanisms that give rise to deglaciations. The leading hypothesis for the forcing of deglaciations is that increasing Northern Hemisphere summer insolation initiates ice-sheet retreat and deglaciation. Alternatively, tropical sea surface temperatures and atmospheric carbon dioxide may lead portions of ice-sheet retreat, implicating them as the driver of deglaciation. Key to discerning between these deglacial-forcing hypotheses is a precise Northern Hemisphere ice-sheet margin chronology. Of the Northern Hemisphere ice sheets, the southern LIS descended to the lowest latitude and should have had the highest climate sensitivity. It is thus an ideal location to study the mechanisms driving initial ice retreat. Despite over 40 years of chronologic research, however, the southern LIS chronology remains incomplete. While the LIS retreat chronology is fairly well constrained in Iowa, Illinois, Indiana, Ohio, and New England, a substantial gap in the chronology of initial deglaciation exists in Wisconsin where permafrost conditions at the Last Glacial Maximum preclude the use of traditional radiocarbon dating methods. This new dataset will identify the timing of LIS retreat from terminal moraines in Wisconsin and fill a gap in the southern LIS deglacial chronology. Dates will be compared with other parts of the southern LIS margin chronology, deglacial climate forcings and climate model simulations to determine the major triggers of Northern Hemisphere deglaciation. Broader impacts include support of the doctoral research and education of Ph.D. candidate David Ullman at the University of Wisconsin-Madison along with the education of undergraduate students in the field and the laboratory, introducing them to the fields of glacial geomorphology, paleoclimatology, geochronology, paleogeography and geochemistry. Results and overall concepts from this research will be presented to the public via the Ice Age Trail Alliance (IATA) in Wisconsin to improve the educational focus of the organization with updated signs, placards and posters along the IATA trails and at various visitor centers. The University of Wisconsin-Madison Geology Museum exhibit on the deglacial history of Wisconsin will also be expanded.

这项研究将通过测量来自末端和衰变冰边缘沉积物的冰川沉积的巨石的原位宇宙核素，改善威斯康星州南部月朗文区冰盖（LIS）的撤退年表。 样品位置将跨越一系列气候环境和冰川床条件。 拟议的研究将解决两个假设。 （1）威斯康星州的最初的冰缘撤退与LIS南部的其余部分同步。 （2）增加北方夏季日光降解强迫LIS脱气。 确定冰层撤退相对于破裂，大气温室气体和全球气候的逐步撤退对于理解引起脱胶的机制很重要。强迫脱裂的主要假设是，增加北半球的夏季日光降低会引发冰盖的静修和脱水。另外，热带海面温度和大气二氧化碳可能会导致冰盖静修处的一部分，这意味着它们是脱气的驱动力。这些冰川式假设之间辨别的关键是确切的北半球冰片边缘的时间顺序。在北半球的冰盖中，南部的LIS降到了最低的纬度，应该具有最高的气候敏感性。 因此，它是研究驱动初始冰撤退的机制的理想位置。 尽管经过40年的时间顺序研究，但南部的LIS年代学仍然不完整。 While the LIS retreat chronology is fairly well constrained in Iowa, Illinois, Indiana, Ohio, and New England, a substantial gap in the chronology of initial deglaciation exists in Wisconsin where permafrost conditions at the Last Glacial Maximum preclude the use of traditional radiocarbon dating methods 。 这个新数据集将确定来自威斯康星州终端的LIS撤退的时机，并填补南部LIS冰冰期年表的空白。 将日期与南部LIS边缘年表的其他部分，冰流气候强迫和气候模型模拟进行比较，以确定北半球脱气的主要触发器。 更广泛的影响包括对博士学位和博士学位教育的支持。威斯康星大学麦迪逊分校的候选人戴维·乌尔曼（David Ullman）以及该领域和实验室的本科生的教育，将他们介绍给冰川地球学，古气候学，地球人工学，古地理和地球化学领域。这项研究的结果和总体概念将通过威斯康星州的Ice Age Trail Alliance（IATA）向公众提出，以改善组织的教育重点，并在IATA步道沿线和各个游客中心使用更新的标志，标语和海报。威斯康星大学麦迪逊分校地质博物馆展览也将扩大有关威斯康星州冰川历史的展览。