Postdoctoral Fellowship: OPP-PRF: Tracing Polar Sediments with Short-lived Radioisotopes in 75 years of Arctic and Antarctic Sediment Cores

气候变化对极地地区的影响尤为严重，北极目前的变暖速度几乎是全球平均速度的四倍。极地变暖推动了海岸侵蚀，增加了向沿海海洋输送的沉积物，影响了从初级生产力到碳封存的生态系统过程。迫切需要跟踪沉降速率的变化，以确定当前条件并测量进一步的变化。然而，在极地地区，两种全球最可靠的沉积物示踪剂——放射性同位素铅-210 （210Pb）和铯-137 （137Cs）——产生了不同的结果。为了了解这些放射性同位素在高纬度地区的分布和用途，本研究利用了俄勒冈州立大学海洋和地质储存库中存档的大量极地沉积物岩心，并结合了文献合成的数据。研究结果首次提供了对北极和南极沉积物增生的系统研究。改进我们用来跟踪沉积变化的工具将有助于沿海管理者和决策者了解气候变化是如何影响极地海岸线和海洋环境的，以及当地社区未来应该期待什么。沉积物岩心将分别用α和γ能谱分析210Pb（半衰期为22.3年）和137Cs（半衰期为30.1年）的活度。为了提供与沉积环境相关的背景，还将分析选定的亚样本的沉积物体积密度，粒度分布和有机含量。将对没有可测量的210Pb或137Cs活性的样品子集进行14C分析，以确定样品中缺乏放射性同位素是由于核心太老，真正的表土层缺失，还是因为寿命较短的放射性同位素没有积累。通过对北极和南极沉积物中210Pb和137Cs分布进行全面的空间分析，本研究将实现三个目标：一是测量存档沉积物岩心中短寿命放射性同位素的活度，这是在同位素衰变无法检测之前为科学界提供服务的迫切需要；第二，制作一个全面的全极沉积物增积率图集；最后，对阿拉斯加北部波弗特海沿岸过去60 ~ 125年的沉积速率变化进行时间分析，这是一个生态和经济上重要的地区，由于气候变暖而经历了环境变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Climate change is disproportionately affecting polar regions, with the Arctic now warming nearly four times faster than the global average. Polar warming drives coastal erosion and increases sediment delivery to the coastal ocean, affecting ecosystem processes ranging from primary productivity to carbon sequestration. Tracking changes in sedimentation rate is urgently needed to determine current conditions and measure further change. In polar regions, however, two of the most globally reliable sediment tracers, the radioisotopes lead-210 (210Pb) and cesium-137 (137Cs), have yielded mixed results. To understand the distribution and usefulness of these radioisotopes at high latitudes, this research makes use of a wealth of polar sediment cores archived at the Oregon State University Marine and Geology Repository combined with data synthesized from the literature. Results provide the first systematic study of Arctic and Antarctic sediment accretion. Improving the tools we use to track changes in sedimentation will help coastal managers and decisionmakers understand how climate change is impacting polar coastlines and marine environments, and what local communities should expect in the future.Sediment cores will be subsampled and analyzed for the activities of 210Pb (half-life = 22.3 years) and 137Cs (half-life = 30.1 years) using alpha and gamma spectroscopy, respectively. To provide context related to depositional environment, select subsamples will also be analyzed for sediment bulk density, grain size distribution, and organic content. A subset of samples with no measurable 210Pb or 137Cs activity will be analyzed for 14C to determine whether the lack of radioisotopes in a sample is because the core is simply too old, the true surface layer is missing, or because the shorter-lived radioisotopes did not accumulate. By undertaking comprehensive spatial analysis of the distribution of 210Pb and 137Cs in Arctic and Antarctic sediments, this research will achieve three goals: first, measure the activity of short-lived radioisotopes in archived sediment cores, a service to the science community that is urgently needed before the isotopes decay beyond detection; second, produce a comprehensive pole-wide atlas of sediment accretion rates; and finally, conduct a temporal analysis of sedimentation rate changes over the last ~60 to 125 years along the Beaufort Sea coast of northern Alaska, an ecologically and economically important region experiencing environmental transformation due to climate warming.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.