Collaborative Research: Distinguishing the drivers of benthic foraminiferal faunal change to improve mechanistic interpretations of abrupt hypoxic events in the North Pacific

在上一个冰河时期，北太平洋边缘出现了几次扩大的低氧状况(缺氧)，虽然已经提出了多种潜在的驱动因素，但这些环境变化的原因仍然存在争议。记录低氧的全部动态变化范围和原因，对于理解碳循环过程和与大规模气候变化相关的生物地球化学反馈至关重要。北太平洋的低氧事件预计将在未来变得更加严重，因此了解它们的动态、驱动因素和过去的生态后果可以为管理现在和未来的海洋生态系统资源提供重要信息。IODP考察队在阿拉斯加湾收集的两个沉积物岩心将提供过去60,000年来生态和环境变化的记录，并将用于记录氧合状态的范围，量化氧合变化的生态后果，并评估有机碳通量变化在驱动低氧事件中的作用。两个研究地点(水深680米和3680米)的高沉淀率使高时间分辨率的研究成为可能，这些研究将用于量化氧气变化的突发性和低氧条件的严重程度。这项研究设计允许测试不同环境设置和气候状态下低氧事件的驱动因素和动力学的共性。确定古氧合作用的成熟方法(重点是纹层、块状沉积物Re和过量的Mn、U、Mo)将识别低氧事件。将利用对岩心下部记录中的底栖有孔虫全群落动物数量与在同一样本上测量的独立得出的地球化学指标进行系统比较，以确定与底栖有孔虫动物群变化有关的主要因素，并开发不依赖于现代空间变异性包括时间变异性这一假设的更准确的底栖动物区系指标。对底栖有孔虫动物群不同物种水平组合的定量多变量分析将使研究小组能够评估缺氧事件的相对严重性和突发性，这在依赖氧化还原阈值的地球化学指标中是不可能的。纳入动物群信息也将改善对缺氧和有机碳通量之间关系的评估。该项目产生的多变量动物群和地球化学数据集可以作为模型测试数据，并将改进动物群替代方法，以识别海底环境的变化，确定环境变化的速度，并评估低氧(低氧)事件的机制。将这些高纬度北太平洋地点与已公布的远场数据进行比较，将有助于评估更大的太平洋盆地缺氧的原因和影响。该项目支持EPSCoR州的一名早期职业教师、两名研究生和本科生，他们将通过高级论文和已建立的REU活动与活跃的研究人员联系。通过这个项目，南达科他州矿业与技术学院的学生将有机会接触到俄勒冈州立大学的先进研究设施。此外，这一项目的成果将被纳入两个机构的研究人员开展的公共宣传活动，其中包括STEM活动，旨在惠及女性和美洲原住民初中生和高中生的活动，老年人教育方案，通过SDSMT地质博物馆进行的公共教育，以及通过FutureEarth/Pages进行的年轻国际学生。

During the last ice age, episodes of expanded low-oxygen conditions (hypoxia) developed along the margins of the North Pacific Ocean and, while multiple potential drivers have been proposed, the causes of these environmental changes remain controversial. Documenting the full dynamic range of variability and causes of hypoxia is essential for understanding carbon cycle processes and the biogeochemical feedbacks associated with large-scale climate changes. Low-oxygen events in the North Pacific are expected to become more severe in the future, thus understanding their dynamics, drivers, and ecological consequences in the past can provide important information for managing today's and tomorrow's marine ecosystem resources. Two sediment cores collected by IODP Expedition 341 in the Gulf of Alaska will provide records of ecological and environmental change over the past 60,000 years and will be used to document the range of oxygenation states, quantify the ecological consequences of changes in oxygenation, and evaluate the role of changing organic carbon fluxes in driving hypoxic events. High sedimentation rates at the two study sites (at 680 m and 3680 m water depth) permit high temporal-resolution studies that will be used to quantify the abruptness of changes in oxygenation and the severity of hypoxic conditions. This study design permits testing the generality of the drivers and dynamics of hypoxic events in different environmental settings and climate states. Well-established methods for determining paleo-oxygenation (focusing on laminations, bulk sediment Re, and excess Mn, U, Mo) will identify hypoxic events. Systematic comparisons of benthic foraminiferal whole-community faunal counts in downcore records to the independently derived geochemical proxies measured on the same samples will be used to identify the primary factors associated with benthic foraminiferal faunal change, and to develop more accurate faunal proxies for benthic conditions that do not rely on the assumption that modern spatial variability encompasses temporal variability. Quantitative multivariate analysis of diverse species-level assemblages of benthic foraminiferal faunas will allow the research team to assess relative severity and abruptness of hypoxic events, which is not possible with geochemical proxies that rely on redox thresholds. The incorporation of faunal information will also improve evaluation of the relationship between hypoxia and organic carbon flux. The multivariate faunal and geochemical data sets produced by this project can serve as model test data and will improve faunal proxy methods for recognizing variations in benthic environments, determining rates of environmental change, and evaluating the mechanisms underlying low-oxygen (hypoxic) events. Comparison of these high-latitude North Pacific sites with published far-field data will contribute to assessing the causes and impact of hypoxia in the larger Pacific Basin. This project supports an early career faculty member in an EPSCoR state, two graduate students, and undergraduate students who will connect with active researchers though senior theses and established REU activities. Through this project, students from South Dakota School of Mines and Technology will have access to advanced research facilities at Oregon State University. In addition, results of this project will be integrated into public outreach conducted by researchers at both institutions, which includes STEM activities intended to benefit female and Native America middle and high school students, elder education programs, public education through the Museum of Geology at SDSMT, and young international students though FutureEarth/PAGES.