Late Ordovician Epeiric Sea Circulation, Environmental Change, and Biotic Turnover: Model and Data Synthesis

奥陶纪浅海环流、环境变化和生物周转：模型和数据综合当今地球科学界面临的最困难的问题之一是确定生命历史上灭绝和迁徙的根本原因。在沉积记录中，生物变化，如物种灭绝，往往与环境变化的证据有关，然而，环境变化背后的过程往往是复杂的，人们对此知之甚少。根据沉积记录进行测试的物理系统的数值模型提供了一种方法，可以用来研究生物事件的最终原因。我们建议使用海洋环流的数值模型来确定北美晚奥陶世大灭绝事件的最终原因。在第一部分中，我们假设北美晚奥陶世期间与物种灭绝有关的环境条件的快速变化是由与造山相关的水深、古地理和降水的变化引起的。我们将为两个时间间隔的海洋环流建模，这两个时间间隔跨越环境条件的突然变化和相关的物种灭绝事件。我们将根据海洋条件的沉积指标分布来检验模型结果的有效性。在这项研究的第二部分中，我们将调查海平面、古地理、水深测量和降水等单变量的相对重要性，这些变量在可能导致物种显著灭绝的陆表海快速海洋变化中起着重要作用。在研究物种灭绝的根本原因时，建模的优点是可以分离出单变量，并评估它们对系统的影响。我们将通过确定模型结果与空间和时间动物群变化的匹配程度来确定灭绝事件的合理原因。通过深入了解这些浅海的快速海洋学变化的原因，这项研究对理解地球历史上任何时期的环境变化和灭绝具有广泛的意义，当时浅海是海洋生态系统的重要组成部分。

ABSTRACTLate Ordovician Epeiric Sea Circulation, Environmental Change, and Biotic Turnover: Model and Data SynthesisOne of the most difficult problems facing the earth science community today is identifying the ultimate causes of extinction and migration in the history of life. In the sedimentary record, biotic change such as extinction is often linked to evidence of environmental change, however the processes underlying environmental change are often complex and poorly understood. Numerical models of physical systems that are tested against the sedimentary record provide a means by which the ultimate causes for bioevents can be investigated. We propose to use a numerical model of ocean circulation to determine the ultimate causes for an extinction event in the Late Ordovician of North America.This study has two main components. In the first component we hypothesize that rapid shifts in environmental conditions linked to extinction during the Late Ordovician of North America were caused by changes in bathymetry, paleogeography, and precipitation associated with mountain building. We will model ocean circulation for two time intervals that span the abrupt shift in environmental conditions and related extinction event. We will test the validity of the model results against the distribution of sedimentary indicators of oceanographic conditions. In the second component of the study we will investigate the relative importance of single variables like changes in sea level, paleogeography, bathymetry, and precipitation in producing rapid oceanographic shifts in the epeiric seas that may have caused significant extinction of species. In investigating the ultimate causes of extinction, modeling has the advantage that single variables can be isolated and their effects on the system evaluated. We will identify plausible causes of the extinction event by determining how well the model results match the spatial and temporal faunal changes. By gaining insight into the causes of rapid oceanographic changes in these epeiric seas, this study has broad implications for understanding environmental change and extinction during any time in Earth's history when epeiric seas were important components of marine ecosystems.