Collaborative Research: Refining foraminiferal I/Ca as a paleoceanographic oxygenation proxy for the glacial Atlantic Ocean

该合作项目旨在改进海洋沉积物中化石有孔虫I/Ca比值的使用，作为重建海洋中过去溶解氧水平的代理，溶解氧水平是一个基本变量，因为氧在碳的生物地球化学循环和控制海洋生物分布中起着重要作用。由于气候变暖和富营养化，目前的海洋正处于氧气含量降低和海洋“死亡区”未来扩大的轨道上。“死亡区”是指水域的氧气含量低于生命所必需的阈值的地区。预计下个世纪将发生的全海洋溶解氧水平的变化，其幅度与过去几百万年自然冰期-间冰期旋回期间发生的变化相似。更好地了解过去海洋的氧气历史，特别是氧气消耗的地理和水深范围，可以帮助改进未来的预测。虽然有一些地球化学代用物可以用来重建在遥远的过去地质时期影响整个或大部分全球海洋的极端氧变化，但缺乏对预计在不久的将来会发生的较细微的氧波动敏感的代用物。初步研究中对有孔虫I/Ca的测量显示了区分和重建水柱中中间氧水平的良好潜力。该项目将进一步评估和完善I/Ca作为重建缺氧和缺氧条件的定量代理，氧气水平与人类时间尺度上对海洋生态系统的未来威胁最为相关。该项目的更广泛影响包括支持一名早期职业科学家和两名高级pi，以及两名研究生和几名本科生。公众宣传将通过与当地锡拉丘兹科学博物馆和主流媒体的合作进行。项目团队将对西非边缘一套大型岩心顶部样品中的有孔虫进行I/Ca分析，以进一步开发碘和地下氧水平之间的经验校准。他们将把I/Ca数据与两个独立的氧指标（底栖有孔虫的氮同位素数据和碳同位素梯度）进行比较，目标是上层和深海。然后，研究小组将对大西洋和南大洋不同地区的下芯浮游生物和底栖有孔虫进行I/Ca测量，定量地重建过去氧最小带（OMZ）分布和强度的变化，重点关注大西洋盆地不同深度和不同地区冰川海洋的变化。此外，海洋碘循环的表示将被纳入广泛使用的地球系统模型（cGENIE），从而首次能够进行明确的数据模型比较。研究生和研究生在地球系统建模方面的培训将通过在锡拉丘兹大学举行的为期两天的研讨会提供。该项目将进一步开发一个有前景的缺氧和亚缺氧条件的代理（I/Ca），研究海洋氧合随气候变化的变异性，并提高代理氧数据与地球系统模型之间未来整合的能力。

This collaborative project seeks to refine the use of I/Ca ratios in fossil foraminifera from marine sediments as a proxy for reconstructing past dissolved oxygen levels in the ocean, a fundamental variable because of the role oxygen plays in the biogeochemical cycle of carbon and in controlling the distribution of marine life. The present oceans because of warming and eutrophication are on a trajectory to lower oxygen contents and future expansion of marine "dead zones" - regions where waters have oxygen levels below the threshold necessary for life. Ocean-wide changes in dissolved oxygen levels that are projected to occur over the next century are expected to have magnitudes similar to those that occurred over the natural glacial-interglacial cycles of the last few millions of years. A better understanding of the ocean's oxygen history in the past, especially the geographic and bathymetric extent of oxygen depletion, can help improve future forecasts. While a number of geochemical proxies are available to reconstruct extreme oxygen changes that affected the whole or large parts of the global ocean in the distant geological past, proxies sensitive to the subtler oxygen fluctuations expected to occur in the near-future have been lacking. Measurements of foraminiferal I/Ca in preliminary studies have shown excellent potential to differentiate and reconstruct intermediate oxygen levels in the water column. This project will further evaluate and refine I/Ca as a quantitative proxy for reconstructing hypoxic and suboxic conditions, oxygen levels most relevant to future threats to marine ecosystems on a human time scale. Broader impacts of the project include the support of an early career scientist and two senior PIs, as well as two graduate students and several undergraduates. Public outreach will be through collaboration with the local Syracuse Science Museum and through the mainstream media. The project team will conduct I/Ca analyses of foraminifera from a large suite of core top samples from the west Africa margin to further develop empirical calibrations between iodine and subsurface oxygen levels. They will compare I/Ca data with two independent oxygen proxies (nitrogen isotope data and carbon isotope gradients in benthic foraminifera), targeting both the upper and deep oceans. The team will then apply I/Ca measurements to downcore planktic and benthic foraminifera from a variety of regions in the Atlantic and Southern Ocean to quantitatively reconstruct past variations in the distribution and intensity of the oxygen minimum zone (OMZ), with a focus on changes in the glacial ocean at different depths and in different parts of the Atlantic basin. In addition, a representation of the marine iodine cycle will be incorporated into a widely-used Earth System Model (cGENIE), enabling explicit data-model comparisons for the first time. Graduate and postgraduate training in earth system modeling will be provided through a two-day workshop to be held at Syracuse University. This project will lead to further develop of a promising proxy (I/Ca) for hypoxic and suboxic conditions, investigate the variability of ocean oxygenation with climate change, and advance the capacity for future integration between proxy oxygen data and earth system models.