Tectonic control of the carbon cycle and climate: Resolving the effects of global spreading-rate variations with high temporal resolution over the past 20 Myr

板块构造抬升了山脉，重新排列了海洋盆地之间的连接，重新分配了地球地幔和地表之间的气体，并且可以在各种时间尺度上影响地球的气候。火山活动，其中大部分是板块构造的结果，释放二氧化碳（CO2）到大气中。对这种脱气作用的一级控制来自于与海底扩张和洋中脊地壳构造有关的火山作用以及俯冲带的火山作用。 因此，海底扩张速度的变化可能会导致大气中二氧化碳浓度随时间的变化。该项目旨在调查海底扩张在促成全球冷却8-10摄氏度方面的作用，该全球冷却始于约1600万年前，并持续了至少1200万年。将重建过去2000万年沿全球洋中脊系统扩展速率沿着的变化。这些记录将用于估计海洋地壳生产率和地壳生产过程中的CO2脱气率。 二氧化碳脱气的估计可以与这段时间海洋温度的变化进行比较。研究结果将用于碳循环模型，以评估对大气二氧化碳水平的影响。该项目支持培养一名地球物理学和古气候学研究生。该项目还支持本科生的培训，并将在布朗大学开设一门新课程，利用最新的高时间分辨率板块重建、全球海底结构和磁异常汇编，以及最近得出的这段时间内磁极反转的天文时间尺度。 天文时标提供了一个高度精确的独立测年系统，避免了假设（粗略间隔的）辐射连接点之间的海底扩展是恒定的，也避免了选择特定海脊系统作为模板的需要。新的古温度估计通过烯酮方法将允许连续重建海洋温度0-20百万年。 研究结果将被整合到一个全球碳循环模型中，目的是检验一个假设，即自约1400万年以来，全球扩散速率的减缓导致大气CO2水平下降了数百ppm，并导致全球变冷。

Plate tectonics elevates mountain chains, rearranges connections between the ocean basins, redistributes gasses between the Earth's mantle and surface, and can affect the Earth's climate at a variety of timescales. Volcanism, most of which occurs as a consequence of plate tectonics, releases carbon dioxide (CO2) into the atmosphere. The first-order control on this degassing comes from volcanism associated with seafloor spreading and crustal construction at mid-ocean ridges and volcanism at subduction zones. Therefore, it is likely that changes in the rate of seafloor spreading can cause changes in the atmospheric CO2 concentration over time. This project seeks to investigate the role of seafloor spreading in contributing to a global cooling of 8-10 degrees C that began around 16 million years ago and continued for at least 12 million years. Variations in spreading rate along the global mid-ocean ridge system over the past 20 Myr will be reconstructed. These records will be used to estimate the rates of oceanic crustal production and CO2 degassing during crustal production. The estimates of CO2 degassing can be compared to changes in ocean temperature over this time. Results will be put into models of the carbon cycle to assess the impact on atmospheric CO2 levels. This project supports the training of a graduate student in geophysics and paleoclimatology. It also supports the training of undergraduate students, and the project will lead to a new course at Brown University.This project will produce the first synthesis of global seafloor spreading rates and ocean crustal production for the past 20 Myr using newly available plate reconstructions at high temporal resolution, global compilations of seafloor fabric and magnetic anomalies, and the recently derived astronomical timescale for magnetic polarity reversals over this time period. The astronomical timescale provides a highly precise independent dating system that avoids the need to assume constancy of seafloor spreading between (coarsely spaced) radiometric tie points and the need to choose a particular ridge system as a template. New paleotemperature estimates via the alkenone method will permit a continuous reconstruction of ocean temperatures 0-20 Myr. Results will be integrated into a global carbon cycle model with the aim of testing the hypothesis that a global slowing of spreading rates caused atmospheric CO2 levels to fall by several hundred ppm since ~14 Myr and led to global cooling.