Collaborative Research: Did the Laurentine Ice Sheet Control Abrupt Climate Change?

这是缅因大学和俄亥俄州立大学的合作项目。主要研究人员将从- 25,000 BP（距今几年）的接近稳态平衡，通过与Laurentide冰山爆发（Heinrich事件2和1）相关的可逆的稳态/稳态间转变，以及在- 11,000 BP （Heinrich事件0）的最后一次冰山爆发后跨越不可逆的Laurentide崩塌阈值，对冰川晚期的Laurentide冰盖进行建模。其目标是确定冰盖变化是否可能通过冰盖突变引发气候变化，并调查这些变化的结构。首席研究人员将在冰盖中分离出数百年来的突变机制，这些突变大到足以触发气候变化，这些变化被耦合的全球和区域大气气候模型捕捉为时间“快照”。具体的建模任务是：1)在这个晚冰期的“快照”时间内提供劳伦泰德冰盖周围的气候设置。这包括冰盖上的风场、边界上的原冰期湖泊、北美精细中尺度气候和全球气候；2)提供基础边界条件，并结合内部流场和温度场计算基础质量平衡。这包括基础温度模式、融化和冻结速率以及相关的冰下水文；3)在所选时间框架内，模拟Laurentide冰盖在施加和基本边界约束下的基础热、水文和力学条件；4)确定建模是否能够分离出允许劳伦泰德冰川快速前进和后退的突变机制，这些突变的面积、高度和体积变化大到足以触发由我们的区域和全球气候“快照”捕捉到的气候变化。这个项目对教育推广和当今冰盖的可能行为具有重要意义。教育拓展计划将与高中生互动。他们将能够操纵主要变量，这样他们就可以看到三维计算机模拟劳伦泰德冰盖如何对每个变量做出反应。这一方案将在全球网络上传播。如果劳伦泰德冰原的波动引发了气候变化，那么目前覆盖格陵兰岛和南极洲的冰原也有可能引发类似的气候变化，造成重大的社会、经济和政治后果。评估这种可能性的一种方法是了解内部不稳定机制，这种机制可能导致劳伦泰德冰川范围的突然变化，并将它们与已知的冰川晚期气候变化紧密联系起来。

This is a collaborative project with the University of Maine and Ohio State University. The Principal Investigators will model the late glacial Laurentide Ice Sheet from near steady-state equilibrium at - 25,000 BP (years before present), through reversible stadial/interstadial transitions associated with Laurentide iceberg outbursts (Heinrich events 2 and 1), and across the threshold of irreversible Laurentide collapse after the last iceberg outburst at - 1 1,000 BP (Heinrich event 0). The goals are to determine if ice-sheet changes could have triggered climate changes by abrupt ice sheet change and to investigate the structure of these changes. The Principal Investigators will isolate mechanisms of abrupt change over hundreds of years in the ice sheet that are large enough to trigger climate changes captured as time "snapshots" by coupled global and regional atmospheric climate models. Specific modeling tasks are: 1) to provide the climate settings surrounding the Laurentide Ice Sheet at "snapshots" of time during this late glacial period. This includes the wind field over the ice sheet, proglacial lakes along the border, the fine-resolution mesoscale climate of North America, and global climate; 2) to provide the basal boundary conditions that, together with the internal flow and temperature fields, are used to calculate the basal mass balance. This includes the pattern of basal temperatures, melting and freezing rates, and the associated subglacial hydrology; 3) to model the Laurentide Ice Sheet basal thermal, hydrological, and mechanical conditions within the imposed and basal boundary constraints for the chosen timeframe; and 4) to determine whether modeling will isolate mechanisms of abrupt change that allow rapid advance and retreat of Laurentide ice, with areal, elevation, and volume changes large enough to trigger climate changes that are captured by our "snapshots" of regional and global climate.This project has significance for educational outreach and the possible behavior of present-day ice sheets. The education outreach program will be interactive with high school students. They will be able to manipulate the major variables so that they can view three-dimensional computer simulations of how the Laurentide Ice Sheet responds to each variable. This program will be disseminated on the world-wide web. If fluctuations in the Laurentide Ice Sheet triggered climate changes, then the possibility exists that present-day ice sheets covering Greenland and Antarctica could trigger similar climate changes, with major social, economic, and political consequences. A way to assess this possibility is to understand the internal instability mechanisms that could have caused abrupt changes in Laurentide ice extent, and to tie them firmly to known late glacial climate changes.