Collaborative Research: P2C2--Synchronizing the North American Varve Chronology and the Greenland Ice Core Record Using Meteoric 10Be Flux

非技术性的北美Varve年代学(NAVC)是一个长达近6000年的年度沉淀层序列，沉积在与劳伦蒂冰盖边缘相邻的冰川湖泊中，在上一个冰期覆盖了北美的大部分地区。在这些沉积物被沉积的时候，大约在12,500到18,000年前，气候正在变暖，劳伦蒂冰盖正在迅速缩小。组成北冰洋的沉积物是对在消退的冰缘发生的事件的年度记录，包括冰缘的位置和退缩速度，夏季冰盖融化产生的水流量，以及随着冰缘湖泊排干而周期性发生的大规模冰川湖暴发洪水。这项提议的目标是了解这些事件与格陵兰冰芯记录中记录的同时发生的气候变化的关系，这一点很重要，因为这将有助于了解大冰盖如何对快速气候变暖做出反应，以及ii)因为这一时间段可能与当前冰川和冰盖迅速变暖和可能缩小的时期相似。将NAVC与格陵兰气候记录进行比较的障碍在于，尽管这两个记录都是独立确定日期的，但这些日期的精度只有几百年，这不足以准确确定哪些气候变化与哪些冰川事件有关。该项目将试图通过比较北大西洋公约沉积物和格陵兰冰芯中大气产生的铍-10的记录来解决这个问题。Be-10是一种天然存在的稀有铍同位素，由宇宙射线轰击高层大气产生，在降水中落到地球上。由于地球磁场的变化，Be-10的产量随着时间的推移而发生变化，这些变化在地球上的各个地方同时发生。BE-10被捕获并保存在冰芯和湖泊沉积物等沉积档案中。因此，格陵兰冰芯和北冰洋湖泊沉积物中的Be-10浓度应该呈现出相同的变化规律。通过将这些更改彼此对齐，我们可以将这两个记录放在一个共同的时间刻度上。因此，即使我们不知道格陵兰冰芯记录的特定气候变化发生的确切时间，我们也可以确切地知道当时北冰洋沉积物中记录的冰缘事件正在发生。我们预计我们将能够以几十年的精度匹配这两个记录，这应该足够精确，以确定重要的气候变化和冰盖变化之间的关系。技术上，北美变化年表(NAVC)是一个长达5659年的年度层状沉积物序列(？VARVE？)沉积在北美东部退缩的劳伦蒂冰盖(LIS)附近的湖泊中。它是大约12,500到18,000年前冰缘位置、融化水和沉积物通量以及冰川湖暴发洪水的年度可分辨记录。该项目的目标是将这一变化年表与来自格陵兰冰芯的同期气候记录联系起来。这一点很重要，因为这种相关性将揭示陆地冰缘事件与北大西洋气候变化之间的时间关系，这反过来将揭示晚期冰盖-气候相互作用的未解决的方面，例如，包括：i)LIS边缘的冰川湖暴发洪水对北大西洋气候的影响，ii)北大西洋气候对LIS东南边缘表面消融和退缩的影响，以及iii)这一时期格陵兰持续的寒冷气候与显著的冰缘退缩之间的明显冲突。该团队建议通过比较大气中产生的(流星的)记录，以十年精度将这两个记录关联起来，而与每个记录的绝对年代无关。Be-10在格陵兰冰芯和北冰洋沉积物中的沉降物。到格陵兰冰芯的Be-10通量的十年分辨率记录已经存在。在这里，我们建议在北冰洋不同的沉积物中进行相应的Be-10测量，以i)确定这些沉积物中的Be-10浓度是否记录了Be-10沉降物的变化，以及ii)如果记录了，则生成与现有冰芯记录相当的Be-10沉降物通量记录，以便将两者进行关联。

Non-technical The North American Varve Chronology (NAVC) is a nearly 6000-year-long sequence of annual sediment layers that was deposited in glacial lakes adjacent to the margin of the Laurentide Ice Sheet, which covered much of North America during the last ice age. At the time these sediments were deposited, between approximately 12,500 and 18,000 years ago, climate was warming and the Laurentide Ice Sheet was shrinking rapidly. The sediments that make up the NAVC are an annually resolved record of events that took place at the retreating ice margin, including the position and retreat rate of the ice margin, the flux of water derived from summer melting of the ice sheet, and large glacial-lake outburst floods that occurred periodically as ice-marginal lakes drained. The goal of this proposal is to understand the relationship of these events to climate changes that were occurring at the same time and are recorded in ice core records from Greenland, which is important because i) it will help to understand how large ice sheets responded to rapid climate warming, and ii) because this time period is a potential analog for the current period of rapid warming and likely shrinkage of glaciers and ice sheets. The obstacle to comparing the NAVC with Greenland climate records is that, although both records have been independently dated, the precision of these dates is a few hundred years, which is not precise enough to accurately determine which climate changes are related to which glacial events. This project will try to resolve this issue by comparing records of atmospherically-produced Beryllium-10 in both NAVC sediments and Greenland ice cores. Be-10 is a naturally occuring rare isotope of Beryllium that is created by cosmic-ray bombardment of the upper atmosphere and falls to earth in precipitation. Be-10 production changes through time due to changes in the Earth's magnetic field, and these changes occur everywhere on Earth at the same time. Be-10 is captured and preserved in sedimentary archives such as ice cores and lake sediments. Thus, Be-10 concentrations in the Greenland ice cores and in the NAVC lake sediments should show the same pattern of changes. By aligning these changes with each other, we can place the two records on a common timescale. Thus, even if we do not know the exact time that a particular climate change recorded in the Greenland ice cores took place, we will know exactly what ice-marginal events recorded in NAVC sediments were occurring at that time. We anticipate that we will be able to match these two records with a precision of several decades, which should be precise enough to determine the relationship between important climate changes and ice sheet change.TechnicalThe North American Varve Chronology (NAVC) is a 5659-year-long sequence of annually laminated sediments (?varves?) deposited in lakes adjacent to the retreating Laurentide Ice Sheet (LIS) in eastern North America. It is an annually resolved record of ice-marginal position, meltwater and sediment flux, and proglacial lake outburst floods between ca. 12,500 and 18,000 years ago. The goal of this project is to correlate this varve chronology with contemporaneous climate records derived from the Greenland ice cores. This is important because such a correlation would reveal the temporal relationship between terrestrial ice-marginal events and North Atlantic climate changes, which in turn would shed light on unresolved aspects of late-glacial ice sheet-climate interactions including, for example, i) the effect of proglacial lake outburst floods at the margin of the LIS on North Atlantic climate , ii) the effect of North Atlantic climate on surface ablation and retreat of the southeastern margin of the LIS, and iii) the apparent conflict between sustained cold climate in Greenland and significant ice margin retreat during this time period. The team proposes to correlate these two records at decadal precision, independently of the absolute dating of each of the records, by comparing records of atmospherically-produced (?meteoric?) Be-10 fallout in Greenland ice cores and NAVC sediments. A decadal-resolution record of Be-10 flux to the Greenland ice cores already exists. Here we propose to carry out corresponding Be-10 measurements in varved sediments of the NAVC to i) determine whether or not Be-10 concentrations in these sediments record changes in Be-10 fallout, and ii) if so, generate a record of Be-10 fallout flux comparable to the existing ice-core record so that the two can be correlated.