Variability in oxygen concentrations in Atlantic intermediate waters during the last deglaciation

氧是海洋生物和化学循环的主要成分。它参与光合作用和呼吸作用，将海洋中氧浓度的变化与碳浓度的变化联系起来，并最终与大气中的变化联系起来。随着海洋吸收越来越多的碳，海洋中的氧浓度正在下降，有可能达到足以减少生物多样性的低水平。最后一个冰河期提供了一个自然实验来研究氧浓度在不同气候条件下可能发生的变化，以帮助预测未来可能发生的事情。大多数以前的研究只能区分氧气浓度的相对变化（更高或更低），但在这个项目中，将开发一种新的应用程序，可以定量地限制过去的氧气浓度。在像热带大西洋这样的地区，氧气最低带（OMZs）正在接近，但目前还没有达到完全缺氧的水平，因此确定能够越过这个阈值进入缺氧状态的环境条件至关重要。该项目将促进几名参与者的培训和学习，其中包括一名没有获得NSF支持的早期职业科学家和一名本科生暑期学生。该项目将从热带大西洋西部和热带OMZ东部的一个地点的一套中深度沉积物岩心中获得高质量的U-Th同位素和微量元素数据。这些数据将用于检验关于末次冰消期间底水氧浓度（BW [O2]）的演变的假设，这些变化是对热带东部海洋表面带强度变化的响应。具体来说，该项目旨在了解OMZ的空间范围和绝对大小是如何变化的，以及这些变化如何与中间水通风和碳储存相关。该提案的第一部分涉及BW定量代理系统的方法开发[O2]。以自生铀为参数化沉积[O2]，以Baxs通量为参数化有机碳通量，建立了BW [O2]的综合重建方法。该部分侧重于Demerara Rise，初步数据表明成功应用的可能性很大，然后将Demerara Rise的新数据与阿拉伯海的额外工作以及之前发布的太平洋数据相结合，以展望该方法的全球实用性。本提案的第二个组成部分研究了热带中间水域的氧浓度在过去可能随着纬向环流、经向环流和有机物通量的变化而变化的方式和原因。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Oxygen is a primary component of the biological and chemical cycles of the ocean. Its involvement in photosynthesis and respiration links the changes of oxygen concentration to that of carbon in the ocean, and ultimately in the atmosphere. As the oceans take up more and more carbon, oxygen concentrations in the ocean are declining, with the potential to reach levels low enough to reduce biodiversity. The last ice age provides a natural experiment to investigate how oxygen concentrations may have varied under different climate conditions in order to help forecast what might happen in the future. Most previous studies have only been able to distinguish the relative change in oxygen concentrations (higher or lower), but in this project a new application will be developed that can quantitatively constrain oxygen concentrations in the past. In regions like the tropical Atlantic, where oxygen minimum zones (OMZs) approach but do not reach a total absence of oxygen today, it is critical to pinpoint the environmental conditions that can cross that threshold into an absence of oxygen. This project will promote training and learning for several participants, including one early-career scientist without previous NSF support and one undergraduate summer student.This project will produce high quality U-Th isotope and trace element data in a suite of intermediate depth sediment cores from the western tropical Atlantic and one site under the eastern tropical OMZ. These data will be used to test hypotheses regarding the evolution of bottom water oxygen concentrations (BW [O2]) during the last deglaciation in response to changes in the intensity of the eastern tropical OMZ. Specifically this project seeks to understand how the spatial extent and absolute magnitude of the OMZ has varied , and how these changes may relate to intermediate water ventilation and carbon storage. The first component of this proposal involves method development of a quantitative proxy system for BW [O2]. It parameterizes sedimentary [O2] with authigenic uranium and organic carbon fluxes with Baxs fluxes to generate a comprehensive approach to reconstructing BW [O2]. This component focuses on the Demerara Rise, where preliminary data indicate a high probability for successful application, and then it combines the new data from the Demerara Rise with additional work in the Arabian Sea and previously published data from the Pacific to prospect the global utility of the approach. The second component of this proposal investigates how and why oxygen concentrations in tropical intermediate waters may have varied in the past in response to changes in zonal circulation, meridional circulation, and organic matter fluxes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.