Collaborative Research: Understanding Carbon Isotope Excursions in the Paleozoic: An Integrated Chemostratigraphic & Modeling Approach

合作研究：了解古生代碳同位素偏移：综合化学地层学

• 批准号: 0418335
• 负责人: Lee Kump
• 金额: --
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-09-15 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0418335&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; Carbon; Isotope

ABSTRACTThe amount of variation in the O2 and CO2 contents of the Phanerozoic atmosphere remain fundamental but unresolved questions. The global burial rate of organic carbon, as indicated by the carbon isotopic compositions of marine carbonates (d13Ccarb), is a critical parameter in modeling atmospheric compositions. While previous efforts have been largely focused on the redox significance of long-term, gradual trends (107 yr) in d13Ccarb and their relationship with d34S, a more volatile record that includes numerous short-term events, or isotopic excursions lasting a few million years or less, is becoming apparent. Some of the best evidence for large d13Ccarb excursions and their relationships to disturbances in the Earth's surface environment (as revealed, for example, by mass extinctions) can be found in Paleozoic strata.The proposed research is aimed at the construction of detailed d13Corg, d34Ssulfate, and 87Sr/ 86Sr for two Paleozoic time slices that are characterized by exceptionally large and well-documented d13Ccarb excursions. These Late Cambrian and Early Mississippian events have both been hypothesized to reflect global increases in the rate of organic carbon burial. This project will carry out numerical experiments using coupled box models of the geochemical cycles of C, S, and Sr to test multiple working hypotheses and to develop internally consistent scenarios for changes in the C and S cycles and the implications for atmospheric CO2 and O2 contents. Our focus on high-resolution data sets will allow us to critically examine some of the proposed cause-and effect feedback loops that stabilize the geochemical carbon cycle and thus the CO2 and O2 composition of the atmosphere. For example, burial of organic matter that is not balanced by oxidation of pyrite should increase atmospheric O2 levels (inferred from coupling and phasing ofd13Ccarb, d34Ssulfate), which provides a negative feedback on organic carbon burial through removal of oceanic phosphorus associated with ferric oxides. In addition, the burial of organic matter should lower pCO2 (lowering the net difference between d13Ccarb and d13Corg), cool the climate, and result ultimately in a decrease in continental weathering rates (reducing 87Sr/ 86Sr). A more complete understanding of these two targeted Paleozoic time slices will also provide unique insight into the Earth's climate system at critical geobiological intervals during (1) a worldwide mass extinction of trilobites in the Late Cambrian and (2) the Early Mississippian spread of vascular land plants and subsequent growth of glaciers on Gondwana.Broader Impacts:The research will support graduate and undergraduate student theses at Ohio State, Missouri and Penn State, including those from underrepresented groups. Students will receive broad training in field and laboratory settings using a variety of geochemical, stratigraphic and modeling techniques. Students at Ohio State and Missouri will spend time with Kump working with box models at Penn State and join Saltzman in the field, thus facilitating exchange among student groups and exposure to diverse faculty and facilities. The researchers will also be involved in outreach activities beyond the standard dissemination of scientific information at meetings and in peer review publications. Middle-school students will be involved by coordination of fieldwork and classes with a 7th grade science teacher. The chemostratigraphic database assembled will provide key reference sections for the assessment of carbon cycling during the critical time periods. It will promote a better understanding of carbon cycling on geological timescales and its relationship with past climates and ecosystems, which will provide an important societal perspective in the context of the magnitude and impact of human-induced climate change.

中生代大气中O2和CO2含量的变化量仍然是一个基本但尚未解决的问题。海洋碳酸盐碳同位素组成（d13Ccarb）表明全球有机碳埋藏速率是模拟大气组成的一个关键参数。虽然以前的努力主要集中在d13Ccarb的长期，渐进的趋势（107年）的氧化还原意义和它们与d34S的关系，一个更不稳定的记录，包括许多短期事件，或同位素漂移持续几百万年或更短，正变得越来越明显。在古生代地层中可以找到一些最好的证据，证明d13Ccarb大偏移及其与地球表面环境扰动的关系（如质量偏移所揭示的）。 87 Sr/86 Sr的两个古生代时间切片，其特点是异常大的和有据可查的d13Ccarb偏移。这些晚寒武世和早密西西比事件都被假设为反映了全球有机碳埋藏速率的增加。本项目将利用C、S和Sr地球化学循环的耦合箱模型进行数值实验，以检验多种工作假设，并为C和S循环的变化以及对大气CO2和O2含量的影响制定内部一致的情景。我们对高分辨率数据集的关注将使我们能够批判性地研究一些拟议的因果反馈回路，这些回路稳定了地球化学碳循环，从而稳定了大气中的CO2和O2成分。例如，埋藏的有机物，是不平衡的氧化黄铁矿应增加大气中的O2水平（推断从耦合和定相ofd13Ccarb，d34Ssulfate），这提供了一个负反馈有机碳埋藏通过去除海洋磷与氧化铁。此外，有机物的埋藏应降低pCO2（降低d13Ccarb和d13Corg之间的净差异），冷却气候，并最终导致大陆风化率降低（降低87 Sr/86 Sr）。对这两个古生代目标时间段的更全面了解还将为我们提供对地球气候系统在关键地质生物学间隔期间的独特见解，包括（1）寒武纪晚期三叶虫的全球大规模灭绝，以及（2）密西西比早期维管陆生植物的扩散和随后冈瓦纳冰川的生长。这项研究将支持俄亥俄州、密苏里州和宾夕法尼亚州的研究生和本科生论文，包括来自代表性不足群体的论文。学生将在现场和实验室环境中接受广泛的培训，使用各种地球化学，地层学和建模技术。学生在俄亥俄州和密苏里州将花时间与坎普在宾夕法尼亚州立大学与箱模型工作，并加入萨尔茨曼在外地，从而促进学生团体之间的交流和接触到不同的教师和设施。研究人员还将参与在会议上和同行审查出版物上标准传播科学信息以外的外联活动。中学生将参与协调实地考察和课堂与七年级的科学教师。化学地层学数据库将为关键时期的碳循环评估提供关键参考部分。它将促进更好地了解地质时间尺度上的碳循环及其与过去气候和生态系统的关系，这将在人类引起的气候变化的规模和影响方面提供一个重要的社会视角。