A Test for the Interpreted Cause of the Mid-Miocene "Monterey Excursion" Using the Boron Isotopic Composition of Benthic Foraminifera

利用底栖有孔虫硼同位素组成检验解释中中新世“蒙特雷漂移”的原因

• 批准号: 9726009
• 负责人: N. Gary Hemming
• 金额: $ 10.9万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-01-01 至 2000-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9726009&HistoricalAwards=false
• 关键词: Test; Interpreted; Cause; Mid; Miocene

9726009 Hemming A major challenge to earth scientists is to document past changes in the earth's atmosphere and chemistry, and to constrain the causes of those changes. We propose to use the boron isotopic composition of mid-Miocene benthic foraminifera to test the hypothesis of Woodruff and Savin (1991) that the "Monterey Excursion", a time of anomalously high d13C compositions in benthic foraminifera, was the result of carbon fixation which lowered atmospheric CO2. The boron isotopic composition of foraminifera is an ideal way to test this hypothesis, as the lower pCO2 should result in higher ocean pH (and hence higher d11B values) at this interval. The ability to determine paleo-pH will allow us to better understand the CO2-H2O equilibrium between oceans and atmosphere in the past, which will contribute to our knowledge of global climate change and the processes that lead to glaciations. This in turn may help us to better understand recent changes in earth's chemistry, such as the 30% increase in atmospheric CO2 that resulted from fossil fuel burning. Recent evidence suggests that the boron isotopic composition of carbonates is controlled by the pH of their parent fluid (e.g., Vengosh et al., 1991; Hemming and Hanson, 1992; Spivack et al., 1993; Hemming et al., 1995). Success in the application of boron isotopes as a pH proxy for Pleistocene glacial oceans (Sanyal et al., 1995; Sanyal et al., in press) lays the foundation for looking at ocean chemistry further back in geologic time. The viability of this tool is dependent on preservation of a primary marine signal in the foraminifera. The marine composition appears to be preserved in the samples studied by Sanyal et al. (1995), but preservation needs to be evaluated in older samples. The time interval of interest to our study was a period of particularly high preservation, so we are reasonably confident that it will be possible to determine primary marine boron isotope signatures through the mid-Miocene.

9726009 Hemming 地球科学家面临的一个主要挑战是记录过去地球大气和化学的变化，并找出这些变化的原因。 我们建议使用中新世中期底栖有孔虫的硼同位素组成来检验 Woodruff 和 Savin (1991) 的假设，即“蒙特利偏移”（底栖有孔虫 d13C 组成异常高的时期）是碳固定降低大气 CO2 的结果。 有孔虫的硼同位素组成是检验这一假设的理想方法，因为较低的 pCO2 应导致该区间的海洋 pH 值较高（因此 d11B 值较高）。 确定古 pH 值的能力将使我们能够更好地了解过去海洋和大气之间的 CO2-H2O 平衡，这将有助于我们了解全球气候变化和导致冰川作用的过程。 这反过来可能有助于我们更好地了解地球化学的近期变化，例如化石燃料燃烧导致大气中二氧化碳含量增加了 30%。 最近的证据表明，碳酸盐的硼同位素组成受其母体流体的 pH 值控制（例如，Vengosh 等人，1991 年；Hemming 和 Hanson，1992 年；Spivack 等人，1993 年；Hemming 等人，1995 年）。 硼同位素作为更新世冰川海洋 pH 值代理的成功应用（Sanyal 等，1995；Sanyal 等，正在出版）为进一步研究地质时期的海洋化学奠定了基础。 该工具的可行性取决于有孔虫中原始海洋信号的保存。 Sanyal 等人研究的样本中似乎保留了海洋成分。 (1995)，但需要在较旧的样本中评估保存情况。 我们研究感兴趣的时间间隔是保存特别高的时期，因此我们有理由相信，有可能确定中新世中期的主要海洋硼同位素特征。