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

最近的记录表明，海洋中的氧气水平正在下降。因此，氧气最低限度区域(OMZ)得到了加强和扩大。然而，海洋溶解氧的测量在时间上受到限制(自20世纪50年代以来)，阻碍了对海洋氧的长期趋势的观测。更好地了解过去的海洋氧气对于了解未来气候变化的影响将是有价值的。该项目将把海洋氧气记录延伸到20世纪以后的地质历史中。该项目将针对气候暖期和冷期之间的过渡来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替代物进行重建。有孔虫壳体的孔隙度代表了OMZ中局部的氧，而铊同位素反映了全球的氧含量。因此，这项研究将比较将被研究的两个不同OMZ内的全球和局部海洋氧气变化。该项目将支持两名女性早期职业科学家和本科生。其他外展项目将利用伍兹霍尔科学和技术教育伙伴关系，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，调查当地和全球通过倒数第二个冰川周期对千禧年气候变化的反应。近年来，底栖有孔虫表面孔隙度已被开发为氧极小区底水溶解氧浓度的定量替代指标，而海水Tl同位素组成已被证明通过锰氧化物埋藏通量的变化来追踪全球海洋氧含量。因此，将这两项分析结合起来，将使人们能够同时了解氧气最小地带和全球海洋氧气对气候状态变化(冰期和间冰期)的反应，以及对(消融)期间高分辨率瞬时气候振荡的反应。这一目标将通过阿拉伯海和南加州边缘氧气最低限度地带的沉积物岩心来实现。这项研究将检验以下假设：(1)与上一次间冰期相比，冰期阿拉伯海和加利福尼亚州的氧气最低带较弱；(2)冰期全球海洋氧气库存较低；(3)全球氧气含量与大气二氧化碳密切相关。因此，这项研究可以评估两个最低含氧区的全球海洋氧合扰动和局部海洋氧合扰动，以及对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伍兹霍尔海洋研究所的班级访问、年度参观和研究讲座，以帮助当地学校教师制定科学课程和提高气候知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.