Doctoral Dissertation Research: Developing A Holocene Chronology of the Laurentide Ice Sheet, North America

末次盛冰期，北半球冰盖在区域到半球的尺度上影响了大气环流模式和气候。这些冰盖的退缩导致了这些环流模式的变化，它们的融化提高了海平面。劳伦泰德冰原是北半球最大的冰原，在冰川消融期间对气候和海平面上升的影响最大。虽然它的退缩到更新世-全新世过渡时期（大约11700年前）相对来说受到放射性碳年代的限制，但劳伦泰德冰盖随后的全新世年代学却鲜为人知。全新世缺乏年代学上的控制，导致对冰盖在气候变化和海平面上升中的作用的基本认识存在很大的不确定性。为了帮助解决这些问题，这个博士论文研究改进项目将利用铍-10对从马尼托巴中部到魁北克-拉布拉多边境的两条横带上的巨石进行定年，为劳伦泰德冰盖开发一个全新世退缩年表，这两条横带是劳伦泰德冰盖的最终位置。将收集30个样品，并使用加速器质谱法分析铍-10的含量。铍-10在岩石中的积累取决于暴露在大气中的时间，通过测量表面中铍-10的含量，可以确定表面的暴露年龄。这项研究的结果将限制劳伦泰德冰盖退缩和最终消亡的时间，从而大大提高对冰盖对气候和海平面变化的贡献的认识。它还将更好地了解冰盖对气候变暖的反应。辨别最后一个北半球大冰盖对气候变暖的敏感性，将有助于预测在当前变暖条件下格陵兰冰盖的未来。劳伦泰德冰盖的年代学也将有助于解决全新世早期至中期气候的环流模式模拟与古代用气候记录之间的分歧。根据这一年表，将估算出由劳伦泰德冰盖引起的全新世海平面上升量。这将提高对南极冰盖海平面上升幅度的理解，南极冰盖是另一个全新世海平面显著变化的唯一来源。考虑到全球变暖对南极冰盖的预期影响，这些估计将有助于预测由于南极冰盖持续消融而导致的海平面上升幅度。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

During the Last Glacial Maximum, Northern Hemisphere ice sheets affected atmospheric circulation patterns and climate at scales ranging from the regional to the hemispheric. Retreat of these ice sheets caused shifts in these circulation patterns, and their melting raised sea level. The Laurentide Ice Sheet was the largest of the Northern Hemisphere ice sheets and had the greatest effect on climate and sea-level rise during deglaciation. While its retreat up to the Pleistocene-Holocene transition, approximately 11,700 years ago, is relatively well constrained by radiocarbon dates, the subsequent Holocene chronology of the Laurentide Ice Sheet is poorly known. This lack of chronologic control in the Holocene has led to large uncertainties in basic understanding of the ice sheet's role in climate change and sea-level rise. To help resolve these issues, this Doctoral Dissertation Research Improvement project will develop a Holocene retreat chronology for the Laurentide Ice Sheet using Beryillium-10 dating of boulders along two transects from central Manitoba to the Quebec-Labrador border, the final location of the Laurentide Ice Sheet. Thirty samples will be collected and analyzed for Beryillium-10 content using accelerator mass spectrometry. The accumulation of Beryillium-10 in rock is dependent upon the period of exposure to the atmosphere, and by measuring the amount of Beryillium-10 in a surface, the exposure age of the surface can be determined.Results from this study will constrain the timing of retreat and ultimate demise of the Laurentide Ice Sheet, thus significantly improve knowledge regarding the ice sheet's contribution to climate and sea-level change. It also will provide a better understanding of the ice sheet's response to a warming climate. Discerning the sensitivity of the last, large Northern Hemisphere ice sheet to a warming climate will aid in predicting the future of the Greenland Ice Sheet under the present warming conditions. This chronology of the Laurentide Ice Sheet also will help resolve disagreements between general circulation model simulations of early to mid-Holocene climate and paleo-proxy records of climate. From this chronology, the amount of Holocene sea-level rise attributable to the Laurentide Ice Sheet will be estimated. This will improve understanding of the amount of sea-level rise from the Antarctica Ice Sheet, which was the only other Holocene source of significant sea-level change. These estimates will help predict the amount of sea-level rise yet to come from continued deglaciation of the Antarctic Ice Sheet given anticipated effects of global warming on this ice sheet. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.