Extensive Readvance of Late Pleistocene (Younger Dryas?) Alpine Glaciers in the North Cascades, Washington, Following Retreat of the Cordileran Ice Sheet

伊斯特布鲁克9628624这项提议是为了使用14C和10Be方法绘制和测定晚更新世冰川的年龄，这些冰川代表了华盛顿州北喀斯喀特地区的气候突变，其年龄与年轻的仙女木相当。该建议的目标包括：(1)识别、绘制这些晚更新世冰川事件的地图并确定其年代；(2)确定受太平洋气旋天气系统控制的西海岸的这些气候变化与北美两侧北大西洋的气候逆转之间是否存在显著的滞后时间；(3)建立与落基山脉类似事件的可能联系。在将要填图和确定年代的冰雹中，有(1)9个明显的YD(？)在科迪勒冰盖从科迪勒兰冰盖的最大冰原和位于喀斯喀特山脉东侧的科迪勒兰冰盖的奥卡诺根小叶的退缩冰原消失后，华盛顿州北部喀斯喀兹山脉高山冰川的冰雹从其源头向下再上升了20-50公里。由于YD事件最初是在欧洲和格陵兰岛记录和确定日期的，所以它被归因于北大西洋不断变化的条件。尽管有证据表明，大约在YD时期，华盛顿西北部的科迪勒冰盖在冰后期重新抬升，但在北美东部和中部明显缺乏YD证据的情况下，人们普遍认为，这样的事件不会影响北美。如果北大西洋的YD冷却同时影响到北美西海岸，反映了北大西洋的气候变化。直到最近，在喀斯喀特山脉还没有发现YD高山冰川的推进，但有新的证据表明，高山山谷冰川系统比科迪勒兰冰盖年轻得多，而且比落基山脉的YD冰川重新推进的程度要大得多。最近在北喀斯喀兹的Nooksack排水系统中发现了这种细菌，就在科迪勒兰冰盖再推进的Sumas山脉Mora ines以南。在评估北大西洋事件导致YD气候逆转的有效性时，最大的问题之一是，这个时代的冰雹很少有适合14C测年的有机物质，因此它们的年龄仍然是推测的。然而，不仅有有机物质可以用来测定北喀斯喀斯特地区的YD冰雹的年龄，而且冰雹上巨大的不稳定巨石也可以用10Be测年。为该项目提出了一种多管齐下的方法：(1)识别和测定代表晚更新世冰川消融期间气候逆转的冰雹：14C和10Be的准确性将使我们能够区分晚冰川脉冲，并表明北美西部是否存在一致的模式。目前，太平洋西北部已知“疑似”的YD冰雹，但它们的年代并不准确--这个问题可以通过14C和10Be测年来解决。在相隔甚远的地区识别出持续的晚冰期后最大脉动，将是我们理解全球气候变化的一大进步。(2)证明了北美西北部冰川晚期与落基山的同步性(或缺乏同步性)。与落基山脉的YD冰川建立关联。在其他地方，将使用从冰川上的巨石中每克10Be的原子进行比较，而不是计算年龄，以减少与10Be生产率有关的准确性问题。此外，将测量26Al，将使用新开发的地磁通量变化修正因子，并将计算的10Be年龄与来自有机物质的14C年龄进行比较。这项调查的结果将被用来建立与中大陆落基山脉中的冰雹年代的对比。以及北大西洋发生的事件。如果能够证明年龄的同步性，它们将对北大西洋事件作为气候突变原因的有效性产生重大影响。

Easterbrook 9628624 This proposal is for mapping and dating late Pleistocene moraines that represent abrupt climatic reversals in the North Cascades of Washington that are equivalent in age to the Younger Dryas, using both 14C and 10Be methods. Among the objective of this proposal are: (1) to identify, map, and date these late Pleistocene moraines, (2) determine if a significant lag time occurred between these climatic changes on the west coast, controlled by cyclonic weather systems of the Pacific Ocean, and climatic reversals in the North Atlantic Ocean on opposite sides of North America, and (3) to establish possible correlations with similar events in the Rocky Mts. Among the moraines that will be mapped and dated are (1) nine apparent YD (?) moraines of alpine glaciers in the North Cascades of Washington that readvanced 20-50km downvalley from their sources following disappearance of the Cordilleran Ice Sheet from the maximum moraine and recessional moraines of the Okanogan lobe of the Cordilleran Ice Sheet on the east side of the Cascade Range. Because the YD event was first recorded and dated in Europe and Greenland, it has been attributed to changing conditions in the North Atlantic. Despite evidence for a late-glacial readvance of the Cordilleran Ice Sheet in northwestern Washington at about the time of the YD, the apparent absence of evidence for the YD in eastern and central North America led to a generally-held belief that such an event did not affect North America. If the YD cooling of the North Atlantic simultaneously affected the west coast of North America, reflecting climatic changes in the North Atlantic. Until recently, no YD alpine glacial advances had been recognized in the Cascade Range, but, new evidence for an extensive system of alpine valley glaciers younger than the Cordilleran Ice Sheet and of much greater extent than the YD glacial readvance in the Rocky Mts. has recently been discovered in the Nooksack drainage of the North Cascades, just south of the mora ines of the Sumas readvance of the Cordilleran Ice Sheet. One of the greatest problems in assessing the validity of events in the North Atlantic as causing the climatic reversals of the YD is that moraines of this age rarely have organic material suitable for 14C dating, so their ages remain speculative. However, not only is organic material available for dating of YD moraines in the North Cascades, but large erratic boulders on moraines are also available for 10Be dating. A multi-pronged approach is proposed for this project: (1) Identifying and dating moraines that represent climatic reversals during late Pleistocene deglaciation: The accuracy of 14C and 10Be will allow the distinguishing of late-glacial pulses and demonstration of whether or not a consistent pattern is present in western North America. At present, "suspected" YD moraines are known in the Pacific Northwest, but they are not well dated--a problem that can be resolved by 14C and 10Be dating. Recognition of a persistent post-late-glacial-maximum pulse in widely separated localities will be a big step forward in our understanding of global climatic changes. (2) Demonstrating the synchroniety (or lack of it) of late glacial moraines in northwestern North America and the Rocky Mts. To establish correlations with the YD moraines in the Rocky Mts. and elsewhere, comparison of atoms per gram of 10Be from boulders on moraines, rather than calculated ages, will be used to minimize accuracy problems related to 10Be production rates. In addition, 26Al will be measured, newly developed corrections factors for geomagnetic flux variations will be used, and calculated 10Be ages will be compared with 14C ages from organic material. The results of this investigation will then be used to establish correlations with dated moraines in the mid-continent Rocky Mts. and events in the North Atlantic. If synchroneity of ages can be demonstrated, they will have significant implications of the validity of events in the North Atlantic as the cause of abrupt climatic changes.