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。结果，氧气最小区（OMZ）得到加强和扩大。然而，海洋溶解氧的测量在时间上是有限的（自20世纪50年代以来），阻止了长期海洋氧趋势的观察。更好地了解过去的海洋氧气对于了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从世纪延伸到地质学的过去。该项目将针对温暖和凉爽气候时期之间的过渡，以测试海洋氧气对气候变化的反应。过去的氧气水平将使用两个不同的代理重建。 有孔虫壳的孔隙度是一个代理氧气在OMZ本地，和铊同位素反映全球的氧含量。因此，这项研究将比较两个不同的OMZ内的全球与当地海洋氧气变化。该项目将支持两名女性早期职业科学家和本科生。额外的推广计划将利用伍兹霍尔科技教育伙伴关系与教师合作，为K-12学校制定科学课程。该项目将利用底栖有孔虫表面孔隙度和铊同位素，调查当地和全球氧气通过倒数第二次冰期循环对千年气候变化的反应。底栖有孔虫的表面孔隙度最近被开发为在氧气最小区的底层水溶解氧浓度的定量代理，而海水铊同位素组成已被证明跟踪全球海洋的氧含量通过锰氧化物埋藏通量的变化。因此，将这两种分析结合起来，就可以同时了解最低含氧量区和全球海洋含氧量对气候状态（冰期和间冰期）变化的反应，以及对冰期（去冰期）期间高分辨率瞬时气候振荡的反应。这一目标将通过来自阿拉伯海和南加州边缘氧气最低区的沉积物芯来实现。该研究将检验以下假设：（1）与末次间冰期相比，冰期阿拉伯海和加州的氧气最低值区较弱;（2）冰期全球海洋氧气存量较低;（3）全球氧气含量与大气CO2之间的密切相关性。因此，这项研究可以评估全球与当地的海洋氧扰动在两个氧气最低区和海洋呼吸碳储存的潜在影响。该项目将支持两名女性早期职业科学家和本科生。与伍兹霍尔科技教育伙伴关系合作的外展计划将包括班级访问和年度图尔斯以及在伍兹霍尔海洋研究所的研究会谈，以帮助当地学校教师开发科学课程和提高气候素养。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.