Collaborative Research: Detrital Cosmochronology of the Greenland Ice Sheet

了解格陵兰冰盖（GIS）的历史，以确定冰盖何时比现在小，对于理解大气中二氧化碳水平的增加和气候变暖至关重要。首席研究员将把以前减少的地理信息系统与其他气候和环境参数联系起来，并为预测其未来行为提供基础。对从冰盖下收集的样品中原位产生的宇宙起源核素的测量，有可能通过对同位素比率的分析（即埋藏年代测定）来确定过去冰川消融的时间。当冰盖减少时，下面的岩石和沉积物暴露在宇宙辐射下，产生具有不同半衰期的放射性核素（10Be, 26Al， 36Cl和14C）。当冰回来时，暴露的表面被掩埋，宇宙射线不再到达曾经暴露的表面。放射性核素的库存得不到生产的支持，并因放射性衰变而开始减少；同位素比率的变化是可以预测的，因为每种同位素都有不同的半衰期。对从GISP2钻孔底部收集的岩石进行的初步多同位素宇宙成因分析表明，顶峰地区的冰川消融约为0.5 ky，这引发了人们的担忧，即当气候变暖时，冰盖可能会完全崩解，也许不会重新形成。首席调查员将通过研究冰下侵蚀的产物，并确定格陵兰岛何时无冰或部分无冰，来研究深层冰取芯的另一种方法。这些结果有可能告诉我们，在过去几百万年里，地理信息系统是如何对主要气候变暖的间隔做出反应的。智力优势：这项研究将依靠冰下侵蚀来取样以前暴露的岩石表面和沉积物。它将提供以前无法获得的关于地理信息系统的信息，方法是使用同位素比率分析来确定地理信息系统下面的岩石和沉积物暴露于宇宙辐射的过去时间。冰流和冰川排水将沉积物运送到冰边缘，在那里他们将直接从露头的冰中收集和分析碎屑。首席研究人员将分析埋葬年龄的人口，以确定初始暴露时间的模式，从而推断过去主要的冰川退缩时间。为了解释冰川学背景下的同位素数据，他们将使用现有的冰流和热模型来推断基本条件和碎屑运输历史。同位素数据将表明冰川侵蚀效率。由于大多数宇宙辐射的穿透深度只有几米，大量不含宇宙形成核素的碎屑表明冰下侵蚀有效，而许多具有明显埋藏年代的碎屑表明冰下停留时间长，床侵蚀和沉积物运输速率低。更广泛的影响：这种方法应在目前被冰覆盖的其他地区得到广泛应用。GIS收缩的模式年龄将为理解海平面变化的主要驱动因素提供信息，并具有重要的古气候意义。同位素数据将指导未来的冰层取芯工作，特别是对亚冰岩石取样的工作。将资助两名研究生。

ABSTRACTBiermanOPP-0713956FinkelOPP-0713938 Understanding Greenland Ice Sheet (GIS) history to determine when the ice sheet was smaller than today, is critical to understand increased atmospheric CO2 levels and warming climate. The Principal Investigators will associate the previously diminished GIS with other climate and environmental parameters and provide a foundation for predicting its future behavior. The measurement of in-situ-produced cosmogenic nuclides in samples collected from below the ice sheet has the potential to date past episodes of deglaciation through the analysis of isotopic ratios known as burial dating. When the ice cover diminishes, underlying rock and sediment are exposed to cosmic radiation, and radionuclides with differing half-lives (10Be, 26Al, 36Cl and 14C) are produced. When ice returns, exposed surfaces are buried and cosmic rays no longer reach the once-exposed surfaces. The inventory of radionuclides is unsupported by production and begins to diminish by radio-decay; isotopic ratios change predictably because each isotope has a different half-life. Preliminary multi-isotope cosmogenic analysis of rock collected from the bottom of the GISP2 borehole suggests that the summit area was deglaciated about 0.5 ky raising the specter that when climate warms, the ice sheet can disintegrate completely and perhaps not reform. The Principal Investigators will investigate an alternative approach to deep ice coring by studying the products of subglacial erosion and identify when Greenland was ice-free or partially ice-free. The results have the potential to tell us how the GIS responded to intervals of major climate warming over the past several million years.Intellectual Merit: This study will rely on sub-glacial erosion to sample previously-exposed rock surfaces and sediment. It will provide previously unavailable information about the GIS by using isotope ratio analysis to identify past times when the rock and sediment beneath the GIS were exposed to cosmic radiation. Ice flow and englacial drainages deliver sediments to the ice margin where they will collect and analyze clasts directly from outcropping ice. The Principal Investigators will analyze populations of burial ages to determine modes of initial exposure time from which they will infer times of major ice retreat in the past. To interpret isotopic data in glaciological context, they will use existing ice flow and thermal models to infer basal conditions and clast transit histories. Isotopic data will indicate glacial erosion efficiency. Because the penetration depth of most cosmic radiation is only several meters, large numbers of clasts containing no cosmogenic nuclides would indicate efficient sub-ice erosion whereas many clasts with significant burial ages would indicate long subglacial residence times and low rates of bed erosion and sediment transport.Broader Impact: This methodology should have wide application in other areas currently covered by ice. Model ages for GIS shrinkage will provide information for understanding a major driver of sea-level change and have important paleoclimaticimplications. Isotopic data will guide future ice coring efforts, particularly those intended to sample sub-ice rock. Two graduate students will be supported.