Collaborative Research: Did the Laurentide Ice Sheet Cause Abrupt Climate Change?

主要研究人员将模拟晚冰期Laurentide冰盖从接近稳态平衡在-25，000 BP（几年前），通过可逆stadial/interstadial过渡与Laurentide冰山爆发（海因里希事件2和1），并跨越阈值的不可逆Laurentide崩溃后，最后一次冰山爆发在-11，000 BP（海因里希事件0）。 目标是确定冰盖变化是否可能通过冰盖突然变化引发气候变化，并调查这些变化的结构。 主要研究人员将隔离数百年来冰盖突变的机制，这些机制大到足以触发耦合的全球和区域大气气候模型作为时间“快照”捕获的气候变化。 具体建模任务包括：1）提供晚冰期期间劳伦蒂德冰盖周围的气候环境的“快照”。 这包括冰盖上的风场、沿边界沿着的冰前湖、北美的精细分辨率中尺度气候和全球气候; 2）提供基底边界条件，连同内部流场和温度场一起用于计算基底物质平衡。 这包括基底温度的模式，融化和冻结速率，以及相关的冰下水文学：3）在所选择的时间框架内，在所施加的和基底的边界约束下，模拟劳伦蒂德冰盖的基底热，水文和力学条件;以及4）确定建模是否将隔离突然变化的机制，使劳伦蒂德冰的快速前进和后退，与面积，海拔，和体积变化大到足以触发气候变化，我们的区域和全球气候的“快照”捕捉。这个项目具有教育推广和现代冰盖的可能行为的意义。 教育推广计划将与高中学生互动。 他们将能够操纵主要变量，以便他们可以查看劳伦泰德冰盖如何响应每个变量的三维计算机模拟。 该方案将在万维网上传播。 如果劳伦蒂德冰盖的波动引发了气候变化，那么现在覆盖格陵兰岛和南极洲的冰盖可能会引发类似的气候变化，并带来重大的社会，经济和政治后果。 评估这种可能性的一种方法是了解可能导致劳伦蒂德冰范围突然变化的内部不稳定机制，并将其与已知的晚冰期气候变化紧密联系起来。

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.