Reconstructing the paleo-budget of 231Protactinium in the North Pacific

在海水中产生的自然存在的同位素，通过开放海洋中的沉降颗粒输送到深海沉积物中，是物理、化学和生物过程随时间变化的有力指标。最近在北太平洋沉积物中发现的231proactinium （Pa）的埋藏与其在上覆水柱中的产生接近平衡。相比之下，现存的少数较长的沉积记录表明，埋藏的231Pa明显少于过去冰期产生的231Pa，这提高了生物生产力、洋流或海洋化学变化的可能性。该项目将利用一系列来自北太平洋的深海沉积物岩心，从过去的时间间隔中产生高质量的数据集，以调查沉积231Pa预算的变化，并探索这些海洋学可能性。所得数据将用于检验关于231Pa在海洋中的分布和埋藏的假设，并提供对生物生产力、化学海洋学和海洋环流过去变化的见解。该项目将促进不同教育层次学生的培训和学习。研究生将在研究中发挥核心作用，获得技术培训和专业发展。沉积231Pa/230Th是一个广泛使用的代理，可以为现代和过去海洋的环流、地表生产力和热液活动提供有价值的信息。尽管现代北太平洋的231Pa预算似乎处于平衡状态，但沿着盆地边缘埋下的231Pa几乎是今天公海埋下231Pa的两倍。最近从东北太平洋产生的一些记录表明，在上一个冰河时期，沿着边缘的这个主要汇可能没有起作用。事实上，东北太平洋231Pa埋藏似乎随气候条件的变化而变化，过量埋藏只发生在间冰期。该项目将提供一个系统的、定量的评估北太平洋231Pa预算在上一个冰期周期中是如何演变的。该研究将生成231Pa/230Th时间序列和太平洋各主要生物地理省（包括开放海洋环流和周围大陆边缘）的生产力记录，以评估太平洋生物地球化学循环如何随时间演变。这些数据将确定在末次冰期是否以及在何处掩埋了明显缺失的边缘231Pa，评估驱动这一转变的机制，并评估231Pa掩埋的空间分布如何随时间演变。这将允许测试关于北太平洋生物生产力和深海环流潜在变化的假设。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。

Naturally occurring isotopes produced in seawater and delivered to deep-sea sediments by settling particles in the open ocean serve as powerful indicators of changes in physical, chemical and biological processes through time. The recent burial of 231Protactinium (Pa) in sediments of the North Pacific Ocean is observed to be in near balance with its production in the overlying water column. In contrast, the few existing longer sedimentary records suggest that significantly less 231Pa was buried than produced during past ice ages, raising the possibility of changes in biological productivity, ocean currents, or ocean chemistry. This project will produce high quality datasets from past time intervals to investigate changes in the sedimentary 231Pa budget and explore these oceanographic possibilities, using an array of deep-sea sediment cores from across the North Pacific. The resulting data will be used to test hypotheses regarding the distribution and burial of 231Pa in the ocean and to provide insights into past changes in biological productivity, chemical oceanography, and ocean circulation. The project will promote training and learning for students at multiple different educational levels. A graduate student will play a central role in the research, gaining technical training and professional development.Sedimentary 231Pa/230Th is a widely utilized proxy that can provide valuable insight into circulation, surface productivity and hydrothermal activity in the modern and past ocean. Although the modern 231Pa budget in the North Pacific appears to be in balance, almost twice as much 231Pa is buried along the basin margins than in the open ocean today. The few recently generated records from the Northeast Pacific suggest that this major sink along the margins may not have been in effect during the last ice age. In fact, 231Pa burial in the Northeast Pacific appears to vary in tandem with changing climate conditions, with excess burial only occurring during interglacial periods. This project will provide a systematic, quantitative assessment of how the North Pacific 231Pa budget has evolved over the last glacial cycle. The study will generate 231Pa/230Th time series and productivity records from each of the major biogeographic provinces in the Pacific, including the open ocean gyre and surrounding continental margins, to assess how the biogeochemical cycles of the Pacific Ocean have evolved over time. These data will determine whether and where the apparently missing marginal 231Pa was buried during the last glacial period, evaluate the mechanisms that drove this shift, and assess how the spatial distribution of 231Pa burial may have evolved over time. This will allow the testing of hypotheses regarding potential changes in biological productivity and deep ocean circulation in the North Pacific Ocean.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.