Uranium isotopes and past changes in Southern Ocean circulation

海洋环流与地球周围的过程有着深刻的联系，包括大陆冰盖的融化或生长。海洋环流与冰盖变化之间的确切机制可能很难单独使用现代观测来梳理。因此，地质学家从过去的例子中寻找海洋环流何时发生变化以及这些变化如何与过去时代的其他现象联系起来。特别是，已经发现南极底层水的循环，密集的水在南极大陆周围下沉并填充世界最深的地方？南极洲的海洋，可能与南极洲西部冰盖的融化有着非常密切的联系。在低氧条件下形成的南大洋沉积物中天然存在的铀的浓度是一个关键工具，已被用于重建南大洋一个地区约125，000年前一个温暖时期的过去环流变化。 该项目将把这一最近开发的方法应用于南大洋的其他地区和过去的其他时期（最多50万年前），以调查南极洲周围的环流如何与冰盖融化联系在一起的更有力的机制，以及这一机制在未来可能如何变化。 该项目支持早期职业研究人员以及研究生和本科生的研究培训。 将通过开发新课程和通过海洋科学碗比赛等活动与高中学生进行外联。该项目将通过开发一种新的古海洋学替代物来促进基础设施建设，这种替代物有可能更好地约束冰盖融化的模型，并为气候变化和海平面上升相关问题提供信息。为了更准确地重建过去南大洋深部的氧化条件，从而重建南极底层水（AABW）循环，该项目将采用一种新的地球化学方法，利用自生铀（U-234/U-238）的同位素组成，并辅以其他氧化还原敏感金属（Re和Mn）。这种测量的组合允许确定单独的元素代理无法检测到的氧化变化的周期。这种方法将应用于多个南大洋岩心，以测试不同沉积环境的可重复性和敏感性。此外，该项目将调查过去50万年的多个间冰期，以研究AABW对一系列强迫和南极冰盖范围的响应。其结果将是一个强大的视角AABW的变化在间冰期及其与外部强迫（轨道配置，二氧化碳，南大洋生产力）和西南极冰盖融化的关系。

Ocean circulation has deep connections with processes around the Earth including the melting or growing of continental ice sheets. The exact mechanisms linking ocean circulation to ice sheet variability can be difficult to tease out using modern observations alone. Geologists therefore look to the past for examples of when ocean circulation changed and how those changes relate to other phenomena in past eras. In particular, it has been found that the circulation of Antarctic Bottom Water, dense water that sinks around the Antarctic continent and fills the deepest parts of the world?'s ocean, may have a very intimate link with melting of the West Antarctic Ice Sheet. The concentration of naturally-occurring uranium in Southern Ocean sediments, formed under low oxygen conditions, is a key tool that has been applied to reconstruct past circulation changes during one past warm period, ~125,000 years ago, in one area of the Southern Ocean. This project will apply this recently developed method to other areas of the Southern Ocean and to other time periods in the past (up to 500,000 years ago) in order to investigate a more robust mechanism for how circulation around Antarctica is linked to ice sheet melting and how this might change in the future. The project supports an early-career researcher as well the training of a graduate and undergraduate students in the research. Outreach will be accomplished through the development of a new course and with high school students through events such as the Ocean Sciences Bowl competition. The project will contribute to infrastructure by developing a new proxy for paleoceanography, which has the potential to better constrain models of ice sheet melting and inform on issues related to climate change and sea level rise.To more accurately reconstruct past deep Southern Ocean oxygenation conditions, and therefore Antarctic Bottom Water (AABW) circulation, the project will utilize a novel geochemical approach using the isotope composition of authigenic uranium (U-234/U-238), augmented by other redox sensitive metals (Re and Mn). This combination of measurements allows for periods of changing oxidation to be identified that elemental proxies alone could not detect. This approach will be applied in multiple Southern Ocean cores to test for reproducibility and sensitivity to varying sedimentary environments. Furthermore, the project will investigate multiple interglacial periods over the past 500,000 years to examine the response of AABW across a range of forcings and Antarctic Ice sheet extents. The result will be a robust perspective on AABW variability during interglacial periods and its relationship to external forcings (orbital configuration, CO2, Southern Ocean productivity) and West Antarctic Ice Sheet melting.