Doctoral Dissertation Research: Understanding the Relationship Between Cosmic Ray Intensity and the Magnetic Field: A Case Study During the Most Recent Magnetic Reversal

这个博士论文项目是关于量化地磁场的屏蔽作用，以及它如何保护地球表面免受宇宙射线的轰击。 宇宙成因核素（CN）用于划分地貌过程的速率和评估古气候事件的时空变化，因此是古气候重建的重要工具。 然而，由于氯化萘生产率的已知程度有限，因此其实用性有限。 目前，用于确定地表暴露日期的“定标器”的空间变异性主要受纬度和海拔高度的控制。 然而，人们普遍认为，这两个变量并不能准确地解释地球磁场的动态特征及其对氯化萘生成率的调制。 该研究将制定一项战略，量化与Matuyama-Brunhes反转相关的氯化萘生产率和磁场强度之间的关系。这将提供一个独特的评估的敏感性，环境变化率的时间时，磁场强度几乎消失。 数据将从玄武岩中发现的矿物中提取。 熔岩流序列中的每一层玄武岩记录了磁场的方向以及形成时磁场的绝对古强度。 此外，每一层都含有足够的钾，可以用Ar-Ar测年法确定喷发时间。 将采用的战略是，通过测量橄榄石中宇宙成因核素3 He的浓度，建立古氯化萘生产率的时间序列，该浓度是由跨越反转的层状玄武岩地层中的40 Ar-39 Ar测年确定的年龄的函数。 对这些浓度的分析将有助于确定与Matuyama-Brunhes磁反转有关的宇宙射线通量的变化是否可以从氯化萘浓度的变化中确定。对全球环境变化的理解受到对古气候事件及其节奏的理解的限制。 氯化萘表面暴露年代测定被广泛用于确定这种地貌过程的规模和速度，这是气候变化的一个关键指标。 加强对区域氯化萘生产率的了解将有助于更好地确定变化的速度。 此外，科学界尚未确定地磁逆转如何通过增加宇宙辐射影响地球表面。 磁层是地球抵御宇宙辐射的主要屏障，该项目的结果之一可能是更好地定义与逆转相关的宇宙辐射是否有害。 此外，确定磁场逆转期间磁场的地理特征以及对生物或人类活动的任何相关影响，从破坏多个物种的迁移模式到破坏人类空中旅行，对社会具有重大价值。 本研究项目期间收集的经验和数据将用于俄勒冈州的公共宣传计划，并纳入俄勒冈州西部地区男孩女孩俱乐部的计划。 该计划的目标是让中学生接触从事研究项目的科学家，并激励他们努力成为科学家。 作为博士论文研究改进奖，该项目将提供支持，使一个有前途的研究生从一个代表性不足的群体建立一个独立的研究生涯。

This doctoral dissertation project is about quantifying the shielding affects of the geomagnetic field and how it protects earth's surface from the bombardment of cosmic rays. Cosmogenic nuclides (CN) are used to delimit rates of geomorphic processes and to assess spatial and temporal variability of paleoclimatic events, and are therefore a crucial tool in paleoclimatic reconstruction. Their usefulness is limited, however, by how well CN production rates are known. Currently, the spatial variability of 'scalers' used to determine surface exposure dates are controlled largely by latitude and altitude. However, it is widely accepted that these two variables do not accurately account for the dynamic character of earth's magnetic field and its resulting modulation of CN production rates. This study will develop a strategy to quantify the relationship between CN production rates and magnetic field strength associated with the Matuyama-Brunhes reversal. This will provide a unique evaluation of the sensitivity of environmental change rates to a time when the magnetic field strength virtually disappeared. Data will be extracted from the minerals found in basalt. Each layer of basalt within a sequence of lava flows records both the orientation of the magnetic field as well as the absolute paleo-intensity of the field during the time of formation. In addition, each layer contains enough potassium to determine the time of eruption with Ar-Ar dating. The strategy that will be used involves the construction of a time series of CN paleo-production rates by measuring concentrations of the cosmogenic nuclide 3He in olivine as a function of age determined by 40Ar-39Ar dates in layered basalt formations that span the reversal. Analysis of these concentrations will help determine if changes in the cosmic ray flux related to the Matuyama-Brunhes magnetic reversal can be defined from variations in CN concentrations. Efforts to understand global environmental change are limited by the understanding of paleoclimatic events and their pacing. CN surface exposure dating is widely used to define the scale and pacing of such geomorphic processes, which are a key indicator of climate change. An enhanced understanding of regional CN production rates will help better define the pacing of change. In addition, the scientific community has yet to define how geomagnetic reversals impact the surface of the planet by way of increased cosmic radiation. The magnetosphere is earth's primary shield against cosmic radiation and one of the results of this project may be a better definition of whether cosmic radiation associated with reversals is hazardous. In addition, determining the geographic character of the magnetic field during times of magnetic reversal and any associated impacts on biological or human activity ranging from disruption in migration patterns of multiple species to disruption in human air travel is of great value to society. Experiences and data collected during this research project will be used for public outreach programs in Oregon and incorporated into a program for the Boys and Girls Club in the western Oregon area. The program goal is to expose middle and secondary school children to scientists working on research projects and inspire them to work towards careers as scientists. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising graduate student from an under-represented group to establish an independent research career.