Development of Technique: Systematically measuring the cosmogenic 26Al/10Be production ratio at a variety of altitudes and latitudes

技术开发：系统测量不同海拔、纬度的宇宙成因 26Al/10Be 生成比

• 批准号: 1733887
• 负责人: Paul Bierman
• 金额: $ 9.35万
• 依托单位: University of Vermont & State Agricultural College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-04-15 至 2022-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1733887&HistoricalAwards=false
• 关键词: Development; Technique; Systematically; measuring; cosmogenic

Geologists use many rare isotopes of different elements to date events in the past, both natural and those related to humans. One particularly widely applied system compares the ratio of 26Al to 10Be in samples that have been exposed at the surface of the earth and then buried. To create ages from a measured ratio of 26Al/10Be, researchers need to know the ratio of 26Al/10Be after exposure but before burial. While this ratio has been estimated before, its value is not well known and appears to vary around the world. This project will be the first to measure the 26Al/10Be ratio in over 150 different samples that have already been collected and will thus provide the information needed for many researchers in a variety of fields (geology, glaciology, archeology) to generate more accurate 26Al/10Be burial ages. The new data will also allow much better understanding of the uncertainty of these ages. This work will train a graduate student in science and will improve dates of ancient human remains as well as past changes in Earth's climate, including the coming and going of glaciers.Knowing the surface production ratio of 26Al/10Be is critical for the calculation of two-isotope burial ages because a measured 26Al/10Be ratio less than the production ratio can be interpreted quantitatively as the duration of burial after surface exposure of a sample. Although 26Al/10Be dating has been widely applied (and many of the applications have been supported by NSF), the 26Al/10Be ratio at production is not well constrained by data. Recent measurements suggest that the ratio is at least 8% higher in Greenland than the canonical value of 6.75, which is derived primarily from one series of early 1990s measurements made at high elevation in the mid latitudes. Physics-based models and some other new data suggest that the 26Al/10Be surface production ratio should vary systematically with latitude and altitude. Here, this project will test for spatial variance and determine the 26Al/10Be surface production ratio empirically as a function of latitude (5-45° in both hemispheres) and altitude (0 to 5000 meters above sea level.). The team will do this by making 150 high-precision 26Al analyses of archived samples already prepared and previously analyzed for 10Be. The team will compare this data-driven determination of the 26Al/10Be surface production ratio with predictions made using numerical models of nuclide production. The project will increase the broader impact of this work by disseminating the results both at meetings and in at least one peer-reviewed publication. This will ensure that the community is aware of and can easily use the data that are generated to improve the accuracy of 26Al/10Be two-isotope dating. Additional broader impacts include training a student who will do much of the research and writing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地质学家使用不同元素的许多稀有同位素来确定过去发生的事件，包括自然事件和与人类有关的事件，一种应用特别广泛的系统比较了暴露在地球表面然后掩埋的样本中 26Al 与 10Be 的比率。为了根据测量的 26Al/10Be 比率得出年龄，研究人员需要知道暴露后但埋葬前的 26Al/10Be 比率，虽然之前已经估算过该比率，但其值并不为人所知，而且似乎还不清楚。该项目将首次测量已收集的 150 多个不同样品中的 26Al/10Be 比率，从而为各个领域（地质学、冰川学、考古学）的许多研究人员提供所需的信息。生成更准确的 26Al/10Be 埋藏年龄也将有助于更好地了解这些年龄的不确定性。这项工作将培训研究生的科学知识，并将改进古代人类遗骸的年代以及过去的变化。地球气候，包括冰川的进出。了解 26Al/10Be 的表面生成比率对于计算双同位素埋藏年龄至关重要，因为测量的 26Al/10Be 比率小于生成比率可以定量解释为持续时间尽管 26Al/10Be 测年已被广泛应用（并且许多应用已得到 NSF 的支持），但 26Al/10Be 比率在最近的测量表明，格陵兰岛的这一比率至少比标准值 6.75 高出 8%，该标准值主要源自 20 世纪 90 年代初在中纬度高海拔地区进行的一系列测量。基于模型和其他一些新数据表明，26Al/10Be 表面生产率应随纬度和海拔高度而系统变化。在此，该项目将测试空间方差并确定 26Al/10Be 表面。该团队将通过对已经准备好的存档样品和之前的 150 次高精度 26Al 分析来实现这一点。该团队将通过数据驱动确定 26Al/10Be 表面产量比与使用核素产量数值模型进行的预测进行比较，该项目将增加更广泛的影响。这项工作通过在会议和至少一份同行评审出版物中传播结果来进行，这将确保社区了解并能够轻松使用生成的数据来提高 26Al/10Be 双同位素测年的准确性。其他更广泛的影响包括培训将进行大量研究和写作的学生。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Stratigraphic control of landscape response to base-level fall, Young Womans Creek, Pennsylvania, USA

美国宾夕法尼亚州 Young Womans Creek 景观对基准面下降响应的地层控制

• DOI: 10.1016/j.epsl.2018.10.005
• 发表时间: 2018
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: DiBiase, Roman A.;Denn, Alison R.;Bierman, Paul R.;Kirby, Eric;West, Nicole;Hidy, Alan J.
• 通讯作者: Hidy, Alan J.

The Northwestern Greenland Ice Sheet During The Early Pleistocene Was Similar To Today

更新世早期的格陵兰岛西北部冰盖与今天相似

• DOI: 10.1029/2019gl085176
• 发表时间: 2020
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Christ, Andrew J.;Bierman, Paul R.;Knutz, Paul C.;Corbett, Lee B.;Fosdick, Julie C.;Thomas, Elizabeth K.;Cowling, Owen C.;Hidy, Alan J.;Caffee, Marc W.
• 通讯作者: Caffee, Marc W.

Empirical Evidence for Latitude and Altitude Variation of the In Situ Cosmogenic 26Al/10Be Production Ratio

原位宇宙成因 26Al/10Be 生产率随纬度和海拔变化的经验证据

• DOI: 10.3390/geosciences11100402
• 发表时间: 2021
• 期刊: Geosciences
• 影响因子: 2.7
• 作者: Halsted, Christopher T.;Bierman, Paul R.;Balco, Greg
• 通讯作者: Balco, Greg