Evidence for Geomagnetic Field Excursions Recorded in Postglacial (9-15,000 Calendar YBP) Carbonates of the Tahiti Coral Reef

综合海洋钻探计划（IODP）探险队#310最近从塔希提岛周围的礁带中回收了37个珊瑚礁沉积物岩芯。这次考察的总体科学目标是了解塔希提珊瑚礁是如何在过去的18000年里发展起来的，因为全球海平面上升了150多米，这与上一次全球冰期有关。从这些岩心内的651个地层中恢复了古地磁样本，以帮助确定岩心的年代和相互关联。随着珊瑚礁的生长，珊瑚礁沉积物记录了当地磁场的方向；已知的磁场变化提供了大溪地珊瑚礁生长的时间记录。珊瑚中记录的磁场方向也提供了一种将岩心联系起来的方法，并重建了过去1.8万年中不同时期珊瑚礁的样子。本研究的重点是意想不到的观察，来自三个不同时间的18个样本显示了10,700±200 cal. YBP, 12,900±200 cal. YBP和14,200±200 cal. YBP的局部磁场逆转的明确证据。年龄估计来自同一岩心的250多个放射性碳年代。这三种可能的局部逆转（漂移）以前从未被记录过。本研究在可能发生倒转（偏移）的时间间隔内收集了所有岩心的新古地磁样本，以验证这些结果。这项研究有助于了解随着海平面上升，珊瑚礁是如何生长/发展的。这对于了解塔希提珊瑚礁（和其他热带珊瑚礁）将如何随着海平面继续上升而变化是很重要的，这与未来全球变暖有关。了解异常磁场行为的证据对于更好地理解地球外核的磁场发电机源过程也很重要（地球物理学的重大挑战之一）。地球磁场对太阳变化（太阳风、磁暴）起着重要的过滤/缓冲作用；评估地球磁场过滤器在过去是如何运作的，以及它是否可能是全球气候变化的一个因素，这一点很重要。除了该项目的科学目标之外，该奖项还有助于支持一名软钱研究员，他是地球科学中一个代表性不足的群体的成员。该项目还为一名本科生和一名高中生提供培训。研究成果正在通过专业报告、对同行评议的科学文献的贡献进行传播，研究产生的数据集正在通过基于网络的数据库倡议进行传播。

Integrated Ocean Drilling Program (IODP) Expedition #310 recently recovered 37 cores of coral-reef sediments from the current reef tract surrounding the island of Tahiti. The overall scientific goal of this expedition is to understand how the Tahiti coral reef has developed over the last ~18,000 years as global sea level has risen more than 150 meters since the ocean low-stand associated with the last global glaciation. Paleomagnetic samples were recovered from 651 horizons within these cores to help date and correlate the cores. The coral reef sediments record the orientation of the local magnetic field as the coral reef grows; known variations in the magnetic field provide a time record of how the Tahiti coral reef grew. The magnetic directions recorded in the corals also provide a way to correlate the cores and reconstruct what the reef looked like at different times in the last 18,000 years. The focus of this study is the unexpected observation that 18 samples from three different times show clear evidence for local magnetic field reversals at 10,700±200 cal. YBP, 12,900±200 cal. YBP, and 14,200±200 cal. YBP. The age estimates come from more than 250 radiocarbon dates from the same cores. The three possible local reversals (excursions) have never before been recorded. This study is collecting new paleomagnetic samples from all cores in intervals with possible reversals (excursions) to verify these results. This study is helping to understand how coral reefs grow/develop as sea level increases. This is important for understanding how the Tahiti coral reef (and other tropical reefs) will change as sea level rise continues associated with future global warming. Understanding the evidence for anomalous magnetic field behavior is also important to develop a better understanding of the Earth's magnetic-field dynamo source process in the Earth's outer core (one of the Grand Challenges in geophysics). The Earth's magnetic field acts as important filter/buffer for Solar variability (Solar Wind, Magnetic Storms); it is important to evaluate how the Earth's magnetic field filter operated in the past and whether it may have been a factor in global climate change. In addition to the scientific goals of the project, the award is contributing to the support of a soft-money researcher who is a member of an underrepresented group in the earth sciences. The project is also providing training for an undergraduate student and a high school student. Research results are being disseminated through professional presentations, contributions to the peer-reviewed scientific literature, and the datasets generated by the study are being disseminated via web-based database initiatives.