Extremes of Ocean Biogeochemistry: Focus on the Permian-Triassic Boundary

地质证据表明，许多生物和环境危机时期与世界海洋在化学和同位素组成上高度分层的时期相吻合，深海缺氧，可能富含二氧化碳和硫化氢。以化石记录中最大规模的物种灭绝（2.51亿年前）而闻名的晚二叠纪，被认为代表了这样一个间隔。海洋环流的停滞被用来解释这段时间广泛缺氧的极端海洋条件，而环流的重新激活被认为是在全球尼奥斯湖事件中将有毒水带到海洋表面的机制，导致大规模灭绝。这里提出的项目将探索海洋停滞和化学分层之间的关系，以及面对风驱动混合时维持浅水缺氧的机制，使用数值模型来确保所提出的情景符合质量、能量和同位素平衡的基本原则。模型结果将与现有的同位素和岩性数据进行比较。此外，新的硫同位素数据将从世界上最连续和研究最充分的二叠纪-三叠纪边界剖面之一中获得，为评估模型提供重要的生物地球化学信息。建模还将为在特定地区进一步收集数据提供动机和指导。该模型将具有探索缺氧海洋化学的独特能力，因此，它的可用性应该引起科学界的极大兴趣。由此产生的直觉应有助于指导有关气候、海洋环流、海洋生物地球化学和生物反应之间关系的概念模型的后续制定。

Project Summary Geologic evidence indicates that many periods of biotic and environmental crisis coincided with times when the world's oceans were highly stratified in their chemical and isotopic composition, with deep waters that were devoid of oxygen and likely strongly enriched in carbon dioxide and hydrogen sulfide. The Late Permian, notable as the time of the largest mass extinction in the fossil record (251 million years ago), is thought to represent such an interval. Stagnation of ocean circulation has been invoked to explain extreme oceanic conditions of widespread anoxia during this time, and reinvigoration of circulation has been suggested as a mechanism to bring toxic waters to the ocean's surface in a global Lake Nyos-type event, leading to mass extinction. The project proposed here will explore the relationship between ocean stagnation and chemical stratification, and the mechanisms that sustain shallow-water anoxia in the face of wind-driven mixing, using numerical models to ensure that the scenarios proposed are consistent with fundamental principles of mass, energy, and isotopic balance. Model results will be compared with existing isotopic and lithologic data. In addition, new sulfur isotopic data will be obtained from one of the most continuous and well-studied Permian-Triassic boundary sections in the world, providing an important missing piece of biogeochemical information against which to evaluate the models. The modeling will also provide motivation and guidance for further data collection in specific locales. The model will have the unique ability to explore the chemistry of an anoxic ocean, and as such, its availability should be of great interest to the scientific community. The intuition developed should help to guide subsequent formulation of conceptual models concerning the relationship between climate, ocean circulation, ocean biogeochemistry, and biological response.