Collaborative Research: Detrital cosmochronology of the Greenland Ice Sheet

比尔曼OPP-0713956 FinkelOPP-0713938了解格陵兰冰盖的历史，以确定冰盖何时比今天更小，对于了解大气中二氧化碳水平的增加和气候变暖至关重要。首席调查员将把以前缩小的地理信息系统与其他气候和环境参数联系起来，并为预测其未来的行为提供基础。对从冰盖下采集的样品中原位产生的宇宙核素的测量，有可能通过对被称为埋藏测年的同位素比率的分析来确定过去的冰川消退时期。当冰盖缩小时，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(10Be、26Al、36Cl和14C)的放射性核素。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。放射性核素的库存没有生产的支持，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都不同。对从GISP2井底采集的岩石进行的初步多同位素宇宙成因分析表明，山顶地区冰川消融了约0.5公里，这引发了人们的担忧，即当气候变暖时，冰盖可能会完全解体，可能不会发生变化。首席调查员将通过研究冰下侵蚀的产物来调查另一种深冰取芯的方法，并确定格陵兰何时为无冰或部分无冰。这些结果有可能告诉我们，地理信息系统是如何对过去数百万年来主要气候变暖的间隔做出反应的。智力上的优点：这项研究将依靠冰下侵蚀来采样以前暴露的岩石表面和沉积物。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暴露于宇宙辐射的过去时间，从而提供以前无法获得的关于地理信息系统的信息。冰流和冰川排水将沉积物输送到冰缘，在那里他们将直接从露出的冰中收集和分析碎屑。首席调查员将分析埋葬年代的人群，以确定最初暴露时间的模式，根据这些模式，他们将推断过去主要冰川消退的时间。为了在冰川学背景下解释同位素数据，他们将使用现有的冰流和热模型来推断基本条件和碎屑过境历史。同位素数据将表明冰川侵蚀的效率。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，而许多具有较长埋藏年龄的碎屑将表明冰下停留时间长，床层侵蚀和泥沙输移速度低。广泛影响：这种方法应该在目前被冰覆盖的其他地区得到广泛应用。地理信息系统收缩的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工作，特别是那些打算对冰下岩石进行采样的工作。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.