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.

地质学家使用许多稀有的不同元素的同位素来测定过去的事件，包括自然事件和与人类有关的事件。一个特别广泛应用的系统比较了暴露在地球表面然后被掩埋的样品中26Al和10Be的比率。为了根据26Al/10Be的测量比率计算年龄，研究人员需要知道暴露后但埋葬前的26Al/10Be的比率。虽然这一比率以前曾被估计过，但它的价值并不为人所知，而且似乎在世界各地有所不同。该项目将首次在已收集的150多个不同样品中测量26Al/10Be的比值，从而为不同领域(地质学、冰川学、考古学)的许多研究人员提供所需的信息，以产生更准确的26Al/10Be埋葬年龄。新的数据还将让人们更好地理解这些时代的不确定性。这项工作将培养一名科学研究生，并将改进古人类遗骸的年代以及过去地球气候的变化，包括冰川的来去。了解26Al/10Be的地表产生率对于计算两同位素埋藏年龄至关重要，因为测量到的26Al/10Be比值小于产生率，可以定量地解释为样品暴露在地表后的埋藏时间。虽然26Al/10Be测年已经得到了广泛的应用(而且许多应用都得到了NSF的支持)，但生产中的26Al/10Be比值并没有很好地受到数据的约束。最近的测量表明，格陵兰岛的这一比率至少比6.75的标准值高出8%，这主要是根据20世纪90年代初在中纬度高海拔地区进行的一系列测量得出的。基于物理的模型和其他一些新数据表明，26Al/10Be的地表产生率应该随纬度和海拔的变化而系统地变化。在这里，该项目将测试空间差异，并根据经验确定26Al/10Be地表生产率作为纬度(两个半球为5-45°)和海拔(海拔0-5000米)的函数。该团队将通过对已经准备好的存档样本进行150次高精度的26Al分析来实现这一点，并之前对10Be进行了分析。该团队将把这一由数据驱动的26Al/10Be表面产生率的确定与使用核素产生量的数值模型所做的预测进行比较。该项目将通过在会议上和在至少一份经同行审查的出版物上传播成果，增加这项工作的更广泛影响。这将确保社区了解并轻松使用所产生的数据，以提高26Al/10Be双同位素测年的准确性。其他更广泛的影响包括培养一名将从事大部分研究和写作的学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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