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

这一合作项目寻求改进海洋沉积物中有孔虫化石中的I/Ca比率，以此作为重建海洋过去溶解氧水平的替代指标，这是一个基本变量，因为氧在碳的生物地球化学循环和控制海洋生物分布方面发挥了作用。由于变暖和富营养化，目前的海洋正处于降低氧含量和未来扩大海洋“死亡区”的轨道上--这些区域的水域的含氧量低于生命所需的门槛。预计在下个世纪发生的全海洋范围的溶解氧水平变化，其规模预计与过去几百万年的自然冰川-间冰期周期中发生的变化类似。更好地了解海洋过去的氧气历史，特别是氧气耗尽的地理和水深范围，有助于改善未来的预测。虽然有一些地球化学指标可用于重建在遥远的地质过去影响整个或大部分全球海洋的极端氧变化，但对预计在不久的将来发生的更微妙的氧波动敏感的指标一直缺乏。初步研究中对有孔虫I/Ca的测量表明，在区分和重建水柱中的中间氧水平方面具有很好的潜力。该项目将进一步评估和提炼I/Ca，以此作为重建缺氧和亚缺氧条件的量化指标，即在人类时间尺度上与未来对海洋生态系统的威胁最相关的氧气水平。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个人助理，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馆的合作和通过主流媒体进行。项目组将从西非边缘的一大套岩心顶部样本中进行有孔虫的I/Ca分析，以进一步建立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替代指标(海底有孔虫中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，该小组将对大西洋和南大洋不同区域的下部岩心浮游和海底有孔虫进行测量，以定量重建氧最小带(OMZ)的分布和强度过去的变化，重点是冰川海洋在不同深度和大西洋盆地不同部分的变化。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)，首次能够进行明确的数据模型比较。将通过在锡拉丘兹大学举办为期两天的讲习班，提供地球系统建模方面的本科生和研究生培训。该项目将进一步开发一种有前途的低氧和亚低氧条件下的代用数据(I/Ca)，研究海洋氧合作用随气候变化的变化，并提高未来代用氧数据与地球系统模型之间的集成能力。

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.