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，重新安排了海洋盆地之间的连接，重新分配了地幔和地表之间的气体，并可以在不同的时间尺度上影响地球的气候。火山活动大部分是板块构造的结果，向大气中释放二氧化碳(CO2)。这种脱气的一级控制来自与大洋中脊的海底扩张和地壳构造有关的火山作用和俯冲带的火山作用。因此，随着时间的推移，海底扩散速度的变化很可能会导致大气中二氧化碳浓度的变化。该项目旨在调查海底扩散对全球8-10摄氏度降温的贡献，这种降温始于约1600万年前，持续了至少1200万年。将重建过去20年来沿全球大洋中脊系统的扩散速度的变化。这些记录将被用来估计大洋地壳生产和地壳生产过程中二氧化碳脱气的速率。二氧化碳脱气的估计可以与这段时间内海洋温度的变化进行比较。结果将被输入到碳循环模型中，以评估对大气二氧化碳水平的影响。该项目支持对一名地球物理学和古气候学研究生的培训。该项目还支持对本科生的培训，该项目将在布朗大学开设一门新的课程。该项目将利用新获得的高时间分辨率板块重建、海底组构和磁异常的全球汇编以及最近得出的这一时期磁极反转的天文时间刻度，首次合成过去20百万年龄段的全球海底扩张率和洋壳产量。天文时间刻度提供了一个高精度的独立测年系统，无需假定海底在辐射连接点(间隔较大)之间的扩散是恒定的，也不需要选择特定的海脊系统作为模板。通过烯酮方法进行的新的古温度估计将允许连续重建海洋温度0-20 Myr。结果将被整合到一个全球碳循环模型中，目的是检验这样一个假设，即自14年3月以来，全球扩散速度的放缓导致大气二氧化碳水平下降了数百ppm，并导致了全球变冷。

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.