Uranium isotopes and past changes in Southern Ocean circulation

铀同位素和南大洋环流过去的变化

• 批准号: 1658445
• 负责人: Christopher Hayes
• 金额: $ 23.95万
• 依托单位: University of Southern Mississippi
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-06-01 至 2021-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1658445&HistoricalAwards=false
• 关键词: Uranium; isotopes; past; changes; Southern

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.

海洋环流与地球周围的过程有很深的联系，包括大陆冰盖的融化或增长。将海洋环流与冰盖可变性联系起来的确切机制可能很难仅通过现代观测来梳理。因此，地质学家从过去寻找海洋环流何时发生变化的例子，以及这些变化与过去时代的其他现象有何关系。特别是，人们发现，南极底水的循环可能与西南极冰盖的融化有非常密切的联系。南极底水是指在南极大陆周围下沉并充满世界最深处的致密水？？S海洋。南大洋沉积物中天然铀的浓度是在低氧条件下形成的，是重建过去暖期(约12.5万年前)南大洋某一区域环流变化的关键工具。该项目将把这一最近开发的方法应用于南大洋的其他区域和过去的其他时间段(最多50万年前)，以研究南极洲周围的环流如何与冰盖融化有关的更强大的机制，以及这种情况在未来可能会发生什么变化。该项目支持一名早期研究人员，以及对研究生和本科生进行研究培训。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开展外联活动。该项目将通过开发一种新的古海洋学指标来促进基础设施建设，该指标有可能更好地约束冰盖融化模型，并提供与气候变化和海平面上升有关的信息。为了更准确地重建过去南大洋深层氧合条件，从而重建南极底水循环，该项目将利用一种新的地球化学方法，使用自生铀(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识别单靠元素代用品无法检测到的氧化变化时期。这一方法将应用于南大洋的多个岩心，以测试其重复性和对不同沉积环境的敏感性。此外，该项目将调查过去500,000年来的多个间冰期，以检查AABW对各种作用力和南极冰盖范围的反应。其结果将是对间冰期AABW变异性及其与外部作用力(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的一个强有力的视角。

项目成果

Changes in Antarctic Bottom Water Formation During Interglacial Periods

间冰期南极底层水形成的变化

• DOI: 10.1029/2020pa003867
• 发表时间: 2020
• 期刊: Paleoceanography and Paleoclimatology
• 影响因子: 3.5
• 作者: Glasscock, S. K.;Hayes, C. T.;Redmond, N.;Rohde, E.
• 通讯作者: Rohde, E.

Southern Ocean Oxygenation Changes Inferred From Redox‐Sensitive Trace Metals Across Marine Isotope Stage 11

根据海洋同位素第 11 阶段的氧化还原敏感痕量金属推断南大洋氧合变化

• DOI: 10.1029/2021gc009921
• 发表时间: 2021
• 期刊: Geosystems
• 作者: Rohde, E. E.;Hayes, C. T.;Redmond, N.;Glasscock, S. K.
• 通讯作者: Glasscock, S. K.

Global Ocean Sediment Composition and Burial Flux in the Deep Sea

• DOI: 10.1029/2020gb006769
• 发表时间: 2021-04-01
• 期刊: GLOBAL BIOGEOCHEMICAL CYCLES
• 影响因子: 5.2
• 作者: Hayes, Christopher T.;Costa, Kassandra M.;Zhang, Jing
• 通讯作者: Zhang, Jing