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

点击翻译按钮获取中文摘要

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.