From local to global: deciphering oceanic oxygenation responses through the Penultimate Glacial Cycle

最近的记录表明，海洋中的氧气含量正在下降。因此，氧最小带（OMZs）已经加强和扩大。然而，海洋溶解氧的测量在时间上受到限制（自1950年代以来），妨碍了对长期海洋氧趋势的观测。更好地了解过去的海洋氧气对于理解气候变化对未来的影响将是有价值的。这个项目将把海洋氧气记录延伸到20世纪以后的地质历史。该项目将以温暖和凉爽气候之间的过渡为目标，测试海洋氧气对气候变化的反应。过去的氧含量将使用两种不同的代用物来重建。有孔虫壳的孔隙度是OMZ中局部氧含量的代表，而铊同位素反映了全局氧含量。因此，本研究将比较两个不同omz内的全球和局部海洋氧变化。该项目将支持两名女性早期职业科学家和本科生。其他拓展项目将利用伍兹霍尔科技教育伙伴关系与教师合作，为K-12学校开发科学课程。该项目将利用底栖有孔虫表面孔隙度和铊同位素，通过倒数第二次冰期，研究当地和全球氧对千年气候变化的响应。近年来，底栖有孔虫的表面孔隙率已被发展为最低氧带底水溶解氧浓度的定量代理，而海水铊同位素组成已被证明通过锰氧化物埋藏通量变化跟踪全球海洋氧含量。因此，结合这两种分析可以同时了解氧最小带和全球海洋氧对气候状态（冰期和间冰期）变化的响应以及对（去）冰期瞬态气候振荡的高分辨率响应。这一目标将通过来自阿拉伯海和南加州边缘氧气最低带的沉积物岩心来实现。该研究将验证以下假设：(1)与末次间冰期相比，冰期阿拉伯海和加利福尼亚的氧气最低带较弱；(2)冰期全球海洋含氧量较低；(3)全球氧含量与大气CO2密切相关。因此，这项研究可以评估两个氧最小带的全球和局部海洋氧扰动以及对海洋呼吸碳储量的潜在影响。该项目将支持两名女性早期职业科学家和本科生。与伍兹霍尔科学与技术教育伙伴关系合作的外展项目将包括课堂参观、年度参观和伍兹霍尔海洋研究所的研究讲座，以帮助当地学校教师开发科学课程，提高气候素养。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。

Recent records suggest that oxygen levels in the ocean are decreasing. As a result, oxygen minimum zones (OMZs) have intensified and expanded. Yet, measurements of ocean dissolved oxygen have been limited in time (since ~1950s) preventing observations of longer term ocean oxygen trends. Better knowledge of ocean oxygen in the past will be valuable to understand future impacts due to climate change. This project will extend ocean oxygen records beyond the 20th century into the geologic past. The project will target the transition between warm and cool climate periods to test ocean oxygen response to climate change. Past oxygen levels will be reconstructed using two different proxies. The porosity of foraminifera shells is a proxy for oxygen locally in an OMZ, and thallium isotopes reflect global oxygen content. Therefore, this study will compare global versus local ocean oxygen changes within two different OMZs that will be studied. The project will support two female early-career scientists and undergraduate students. Additional outreach programs will use the Woods Hole Science and Technology Education Partnership to work with teachers to develop science curriculum for K-12 schools.This project will investigate both local and global oxygen responses to millennial climate change through the Penultimate Glacial cycle, using benthic foraminiferal surface porosity and thallium isotopes. Surface porosity of benthic foraminifera has recently been developed as a quantitative proxy of bottom water dissolved oxygen concentrations in the oxygen minimum zones, whereas seawater thallium isotopic compositions have proved to track global ocean oxygen content through Mn oxide burial flux variations. Combination of the two analyses would thus allow a simultaneous understanding of oxygen minimum zone and global ocean oxygen responses to the changes of climate states (glacial and interglacial periods) and to high-resolution transient climate oscillations during the (de)glaciation. The goal will be achieved with sediment cores from the Arabian Sea and the Southern California margin oxygen minimum zones. The study will test the hypotheses of (1) weaker Arabian Sea and California oxygen minimum zones in the glacial periods compared to the Last Interglacial; (2) lower global ocean oxygen inventory in the glacial periods; and (3) a close correlation between the global oxygen content and atmospheric CO2. This study thus allows evaluation of global versus local ocean oxygenation perturbations in the two oxygen minimum zones and potential implications on marine respired carbon storage. This project will support two female early-career scientists and undergraduate students. Outreach programs in collaboration with Woods Hole Science and Technology Education Partnership will include class visits and annual tours and research talks at Woods Hole Oceanographic Institution to help local school teachers develop science curriculum and improve climate literacy.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.