Collaborative Research: Development of a novel way for understanding ancient Earth atmospheres and marine sulfate using the stable isotope of Oxygen (17O) in marine barite.

合作研究：利用海洋重晶石中氧（17O）的稳定同位素开发一种了解古代地球大气和海洋硫酸盐的新方法。

• 批准号: 1821958
• 负责人: David Johnston
• 金额: $ 13.38万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-06-15 至 2020-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1821958&HistoricalAwards=false
• 关键词: Collaborative; Research; Development; novel; way

Marine sediments contain a record of climate evolution and how Earth's surface has changed over the last 125 million years. Part of this story is locked up in marine barite (BaSO4), a mineral that precipitates from seawater and contains sulfur and oxygen. Through studies of the stable isotopes in seawater sulfate (SO4), changes in biogeochemical processes and variations in other chemical cycles that are important for life on Earth have been determined. However, due to the properties of this sulfate and its ability to incorporate information from processes as diverse as climate, microbial metabolism and weathering, interpretation of traditional oxygen isotope (18O/16O) and sulfur isotope (34S/32S) measurements commonly result in interpretations that are not unique. This research explores a new, independent means for unraveling the information stored in marine barite via the addition of a previously difficult-to-measure, and hence generally overlooked, isotope of oxygen: 17O. Only recently, with the development of increasingly sensitive mass spectrometers and new laboratory methodologies, have these measurements become possible. The 17O signal locked inside marine barite has the potential to identify the oxygen/carbon dioxide ratio of the atmosphere as well as the intensity of biospheric activity and how these parameters have changed over time, important knowledge for understanding present atmospheric compositions and processes related to global warming. This pilot study analyzes barite in the core tops of ten marine cores to quantitatively evaluate whether barite is a faithful recorder of marine sulfate. To further validate whether 17O can provide a reliable proxy for unraveling the influences of various environmental processes, analyses of samples from additional cores and down core of the those analyzed in the core top study will be carried out. This research further develops and explores the potential of using marine barite to construct a reliable record of the 17O fingerprint of seawater sulfate over the last 125 million years (i.e., from the Cretaceous through the Cenozoic). If successful, the work, in combination with the results of more commonly measured oxygen (18O/16O) and sulfur (33S/32S and 34S/36S) isotope ratios, has the potential to provide insights into the O2/CO2 composition of the atmosphere over time and activity of Earth's biosphere. Although previously 17O measurements of marine barite were difficult to make and had high uncertainties, this limitation has now been overcome by advances in mass spectrometry and the development of laboratory procedures that are tuned to increase the analytical precision of 17O. Goals of the research are to measure 17O in carefully selected barite samples from sediment cores collected from the floor of the Pacific Ocean and quantify the offset, if any, between modern core-top barite and contemporaneous water column sulfate. It will also measure down core variations of 17O to examine variations in the isotope signature with time and compare these with the results from co-existing pore waters to examine possible diagenetic effects. The result will be validation of this new proxy in the marine record. Samples of barite will be extracted from sediment from the tops of ten cores, using acid leaching and other separation techniques to remove all oxygen-bearing phases but barite. The resulting barite will be checked for purity using techniques including scanning and analytical electron microscopy. Preparation of samples for isotope work will include fluorination and analysis on a high resolution isotope ratio mass spectrometer.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.

海洋沉积物记录了过去 1.25 亿年来气候演变以及地球表面的变化。 这个故事的一部分隐藏在海洋重晶石 (BaSO4) 中，这是一种从海水中沉淀出来的矿物质，含有硫和氧。通过对海水硫酸盐 (SO4) 中稳定同位素的研究，已经确定了对地球生命重要的生物地球化学过程的变化以及其他化学循环的变化。然而，由于这种硫酸盐的特性及其整合来自气候、微生物代谢和风化等多种过程的信息的能力，传统氧同位素 (18O/16O) 和硫同位素 (34S/32S) 测量的解释通常会导致解释这并不独特。这项研究探索了一种新的、独立的方法，通过添加以前难以测量、因此通常被忽视的氧同位素：17O，来揭示海洋重晶石中存储的信息。直到最近，随着越来越灵敏的质谱仪和新的实验室方法的发展，这些测量才成为可能。锁定在海洋重晶石内的 17O 信号有潜力识别大气中的氧气/二氧化碳比率以及生物圈活动的强度以及这些参数如何随时间变化，这是了解当前大气成分和与全球相关的过程的重要知识。变暖。这项初步研究分析了十个海洋岩心的岩心顶部的重晶石，以定量评估重晶石是否是海洋硫酸盐的忠实记录者。为了进一步验证 17O 是否可以为揭示各种环境过程的影响提供可靠的代理，将对来自其他岩心和岩心顶部研究中分析的岩心下的样品进行分析。 这项研究进一步开发和探索了利用海洋重晶石构建过去 1.25 亿年（即从白垩纪到新生代）海水硫酸盐 17O 指纹的可靠记录的潜力。如果成功，这项工作结合更常见的氧 (18O/16O) 和硫（33S/32S 和 34S/36S）同位素比测量结果，有可能深入了解大气中的 O2/CO2 组成随着时间的推移和地球生物圈的活动。尽管以前对海洋重晶石进行 17O 测量很难进行且具有很高的不确定性，但现在质谱技术的进步和实验室程序的发展已经克服了这一限制，这些实验室程序经过调整以提高 17O 的分析精度。 该研究的目标是测量从太平洋海底收集的沉积物岩心中精心挑选的重晶石样本中的 17O，并量化现代岩心顶部重晶石与同期水体硫酸盐之间的偏移（如果有）。它还将测量 17O 的核心变化，以检查同位素特征随时间的变化，并将这些结果与共存孔隙水的结果进行比较，以检查可能的成岩作用。结果将在海洋记录中验证这一新代理。将从十个岩心顶部的沉积物中提取重晶石样品，使用酸浸和其他分离技术去除重晶石以外的所有含氧相。 将使用扫描和分析电子显微镜等技术检查所得重晶石的纯度。同位素工作样品的制备将包括氟化和在高分辨率同位素比质谱仪上进行分析。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。