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。将海洋环流与冰盖变化联系起来的确切机制很难仅用现代观测来梳理。因此，地质学家从过去寻找海洋环流变化的例子，以及这些变化与过去时代其他现象的关系。特别是，人们发现南极底水的循环，即围绕南极大陆下沉并填满世界最深处的稠密水？这可能与南极西部冰原的融化有着密切的联系。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，它被用于重建过去一个温暖时期（约12.5万年前）南大洋一个地区过去的环流变化。这个项目将把这种最近开发的方法应用到南大洋的其他地区和过去的其他时期（高达50万年前），以调查一个更强大的机制，了解南极洲周围的环流如何与冰盖融化联系在一起，以及未来这种联系将如何变化。该项目支持一名早期职业研究人员以及研究生和本科生的研究培训。外展将通过开发一门新课程和通过海洋科学碗比赛等活动与高中生一起完成。该项目将通过开发古海洋学的新代理来促进基础设施建设，这有可能更好地约束冰盖融化的模型，并为与气候变化和海平面上升有关的问题提供信息。为了更准确地重建过去的南大洋深部氧合条件，以及南极底水（AABW）环流，该项目将利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，并加入其他氧化还原敏感金属（Re和Mn）。这种测量方法的组合可以确定氧化变化的周期，这是单独的元素代理无法检测到的。该方法将应用于多个南大洋岩心，以测试对不同沉积环境的再现性和敏感性。此外，该项目将调查过去50万年的多个间冰期，以检查AABW对一系列强迫和南极冰盖范围的响应。结果将对间冰期AABW变率及其与外部强迫（轨道结构、二氧化碳、南大洋生产力）和南极西部冰盖融化的关系提供一个强有力的视角。

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.