Collaborative Research: Bringing the Late Pleistocene into Focus: Better Estimates of Ages and Ocean Circulation Through Data-Model Comparison

对过去气候变化的测量对于理解自然气候变化的原因、幅度和速度至关重要。海洋沉积物含有丰富的微化石，这些化石是过去气候信息的重要档案，几乎覆盖全球。为了将海洋沉积物样本放入背景中，研究人员需要两种信息：(1)对该样本所代表的气候的解释；(2)样本的年龄。年龄信息对于重建全球气候变化的速度和顺序至关重要。用放射性碳法测定一些沉积物的年代是准确的。然而，许多样品的年龄只能间接估计，导致年龄不确定度高达4000年。这项研究项目旨在通过对现有放射性碳测年样品的统计分析来改进这些间接年龄估计。间接年龄估计的改进将用于提高过去15万年全球气候变化数据集的准确性。更具体地说，该项目的目的是改进根据海底三角洲18O(全球冰量和深海温度的替代物)的地层比对得出的间接年龄估计。这些年龄的不确定性的一个主要来源是在几个核心区用非常准确的放射性碳模型观察到的海底三角洲18O变化的时间差异，时间长达4000年。然而，关于底栖生物Delta18O信号的时序在其他位置有何不同，我们知之甚少。该项目的研究方法包括海洋环流模型、古气候数据(全球分布的约100个沉积物岩心的海底18O和14C)和统计推断。该项目的第一阶段是利用来自约100个沉积物岩心的放射性碳数据，结合海洋环流模型的结果，在全球范围内表征海底三角洲18O年龄差异(三角洲18O滞后)。第二阶段是应用第一阶段的结果来开发改进的Delta18O比对方法。第三阶段是生成一个改进的Delta18O年龄模型的新数据库。因此，该项目的最终产品将是(1)描述海底三角洲18O变异性的区域和全球模式的概率堆栈(平均值)，(2)多代理岩心比对和生成三角洲18O滞后的贝叶斯推断的概率算法，(3)具有海底三角洲18O数据的约300个岩芯的年龄模型数据库，以及(4)根据海底Del18O数据与不同环流模型情景比较而估计的海洋环流变化。准确的古气候年龄估计对于创建数据汇编至关重要，这些数据汇编用于测试气候模型的有效性，并提高人们对它们模拟未来潜在气候变化能力的信心。古气候数据汇编的空间复盖面往往通过包括具有很大不确定性的间接年龄估计的数据而增加。通过改进海底Delta18O比对的年龄估计和量化比对年龄的不确定性，该项目将能够更明智地选择哪些数据应包括在汇编中，并总体上提高准确性。作为该项目的一部分进行的数据模型比较也将更好地限制海洋环流的变化，这可能有助于描述过去气候变化的因果链条，并可能确定冰川期间孤立的海洋碳库。该项目还将为两名研究生提供地球科学和数学方面的跨学科培训。研究方法和成果将通过开发和传播交互式计算机实验室活动纳入本科生和研究生课堂。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。

Measurements of past climate changes are crucial for understanding the causes, amplitudes, and rates of natural climate variability. Ocean sediments contain abundant microfossils that are an important archive of past climate information with near-global coverage. To place an ocean sediment sample into context, researchers need two kinds of information: (1) an interpretation of the climate represented by that sample and (2) the age of the sample. Age information is crucial for reconstructing the rate and sequence of climate changes globally. Some sediments are well-dated using radiocarbon. However, the ages of many samples can only be estimated indirectly, resulting in age uncertainties as large as 4,000 years. This research project aims to improve these indirect age estimates using statistical analysis of the available radiocarbon-dated samples. Improvements in indirect age estimates will be used to increase the accuracy of global datasets of climate changes for the past 150,000 years.More specifically, the aim of this project is to improve indirect age estimates derived from the stratigraphic alignment of benthic delta18O (a proxy for global ice volume and deep ocean temperature). A major source of uncertainty in these ages derives from differences of up to 4,000 years in the timing of benthic delta18O change observed at a few core sites with very accurate radiocarbon models. However, little is known about how the timing of benthic delta18O signals differs at other locations. The research approach for this project incorporates ocean circulation models, paleoclimate data (benthic delta18O and 14C from ~100 globally distributed sediment cores), and statistical inference. Phase one of the project is to characterize benthic delta18O age differences (delta18O lags) globally using radiocarbon data from ~100 sediment cores in conjunction with results from ocean circulation models. Phase two is to apply the results from phase one to develop improved methods for delta18O alignment. Phase three is to generate a new database of improved delta18O age models. Thus, the final products of the project will be (1) probabilistic stacks (averages) describing regional and global patterns of benthic delta18O variability, (2) probabilistic algorithms for multiproxy core alignments and for generating Bayesian inferences of delta18O lags, (3) a database of age models for ~300 cores with benthic delta18O data, and (4) estimates of ocean circulation changes based on comparing benthic del18O data with different circulation model scenarios.This project has broader impacts for climate change research and education. Accurate paleoclimate age estimates are crucial for creating data compilations that are used to test the effectiveness of climate models and improve confidence in their ability to simulate potential future climate changes. The spatial coverage of paleoclimate data compilations is often increased by including data with indirect age estimates that have large uncertainties. By improving age estimates for benthic delta18O alignments and quantifying alignment age uncertainties, this project will allow for more informed selection of which data to include in compilations and overall better accuracy. Data-model comparison performed as part of this project will also better constrain ocean circulation changes, which could help describe the causal chain of events for past climate changes and may identify isolated reservoirs of carbon sequestered in the ocean during glaciations. This project will also provide interdisciplinary training in earth science and mathematics to two graduate students. Research methods and findings will be incorporated into undergraduate and graduate classes through the development and dissemination of interactive computer lab activities.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.