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今天小，对于了解大气CO2水平增加和气候变暖至关重要。主要研究人员将把以前减少的GIS与其他气候和环境参数联系起来，并为预测其未来的行为提供基础。测量从冰盖下采集的样品中就地产生的宇宙成因核素，有可能通过被称为埋藏年代测定的同位素比率分析，确定过去冰川消退时期的年代。当冰盖减少时，下面的岩石和沉积物暴露于宇宙辐射，并产生不同半衰期的放射性核素（10 Be，26 Al，36 Cl和14 C）。当冰返回时，暴露的表面被掩埋，宇宙射线不再到达曾经暴露的表面。放射性核素的存量不受生产的支持，并开始因放射性衰变而减少;同位素比率的变化是可以预测的，因为每种同位素的半衰期不同。对从GISP 2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，山顶地区的冰川消退了约0.5千年，这让人担心，当气候变暖时，冰盖可能会完全解体，也许不会改革。主要研究人员将通过研究冰下侵蚀的产物来研究深冰取芯的替代方法，并确定格陵兰岛何时无冰或部分无冰。这些结果有可能告诉我们，在过去的几百万年里，地理信息系统是如何对重大气候变暖的间隔作出反应的。智力上的优点：这项研究将依赖于冰下侵蚀，对以前暴露的岩石表面和沉积物进行取样。它将通过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过去暴露于宇宙辐射的时间，从而提供以前无法获得的有关地理信息系统的信息。冰流和冰内水系将沉积物运送到冰缘，在那里他们将直接从露出地面的冰中收集和分析碎屑。主要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，他们将从中推断过去主要冰退缩的时间。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础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，大量不含宇宙成因核素的碎屑将表明有效的冰下侵蚀，而许多具有显着埋藏年龄的碎屑将表明冰下停留时间长，河床侵蚀和沉积物搬运率低。GIS收缩模型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芯取芯工作，特别是那些打算对冰下岩石进行取样的工作。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 paleoclimatic implications. Isotopic data will guide future ice coring efforts, particularly those intended to sample sub-ice rock. Two graduate students will be supported.