Testing the robustness and limitations of 0 – 1 Ma absolute paleointensity data
Testing the robustness and limitations of 0 – 1 Ma absolute paleointensity data
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测试0 – 1 Ma绝对古强度数据的稳健性和局限性
DOI：
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发表时间：
2011
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通讯作者：
C. L. Johnsona
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作者：
L. B. Zieglera;C. G. Constablea;C. L. Johnsona
从热磁化熔岩和考古物体获得的绝对古地磁场强度数据提供了有关过去地磁场行为的信息，但尽管数据集不断增加，平均磁场强度及其变异性以及这些观测数据的预期统计分布仍然不确定。我们使用Perrin和Schnepp[Perrin，M.，Schnepp，E.，2004]编制的数据研究了0-1 Ma磁场的这些问题。IAGA古强度数据库：数据集的分布和质量。太棒了。地球星球。内部147,255-267]，1124个质量参差不齐、覆盖时间和空间有限的样本。在我们的分析中，我们使用虚拟轴偶极矩(VADM)来适应可变空间采样。不均匀的时间抽样导致对平均场及其统计分布的有偏估计。我们使用Bootstrap技术对这些影响进行了校正，得到平均VADM为7.26±0.14×1022 A·m~2。相关的统计分布呈双峰分布，在大约5×1022Am2处有一个副峰。我们评估了这种行为的一系列潜在来源。考虑到作者在0-1 Ma数据集中提供的不确定性，我们没有发现劣质数据污染的明显证据。材料类型的影响是通过独立的数据汇编来评估的，以比较来自熔岩流、海底玄武岩玻璃(SBG)和考古对象的全新世数据。由于年代问题，与SBG的比较没有定论，但来自熔岩的古强度估计平均比考古材料高约10%，并显示出更大的离散性。只有有限的地理抽样偏差测试是可能的。我们将大量的0-0.55 Ma夏威夷数据与全球数据集进行比较，但没有确定的结果。由于排除过渡性数据仍然保持双峰分布，因此不考虑典型的低强度偏移数据过度表示的可能性。没有任何直接测试允许我们排除这样的想法，即观测到的pdf是由对应于磁场的两个可识别的强度状态的两个不同分布的混合而产生的。我们调查了另一种可能性，即我们根本无法恢复假设的更平滑的潜在分布，而时间跨度仅为1 Myr，并且当前数据集的分辨率。基于地磁场频谱的随机模型的模拟表明，长周期强度变化可以对观测到的分布产生强烈的影响，并可以合理地解释表观双峰现象。我们的VADMS的0-1 Ma分布与从沉积物获得的平均相对古强度记录的分布是一致的。©2008 Elsevier B.V.保留所有权利。
Absolute paleomagnetic field intensity data derived from thermally magnetized lavas and archeological objects provide information about past geomagnetic field behavior, but the average field strength, its variability, and the expected statistical distribution of these observations remain uncertain despite growing data sets. We investigate these issues for the 0–1 Ma field using data compiled in Perrin and Schnepp [Perrin, M., Schnepp, E., 2004. IAGA paleointensity database: distribution and quality of the data set. Phys. Earth Planet. Int. 147, 255–267], 1124 samples of heterogeneous quality and with restricted temporal and spatial coverage. We accommodate variable spatial sampling by using virtual axial dipole moments (VADM) in our analyses. Uneven temporal sampling results in biased estimates for the mean field and its statistical distribution. We correct for these effects using a bootstrap technique, and find an average VADM of 7.26 ± 0.14 × 1022 A m2. The associated statistical distribution appears bimodal with a subsidiary peak at approximately 5 × 1022 A m2. We evaluate a range of potential sources for this behavior. We find no visible evidence for contamination by poor quality data when considering author-supplied uncertainties in the 0–1 Ma data set. The influence of material type is assessed using independent data compilations to compare Holocene data from lava flows, submarine basaltic glass (SBG), and archeological objects. The comparison to SBG is inconclusive because of dating issues, but paleointensity estimates from lavas are on average about 10% higher than for archeological materials and show greater dispersion. Only limited tests of geographic sampling bias are possible. We compare the large number of 0–0.55 Ma Hawaiian data to the global data set with no definitive results. The possibility of over-representation of typically low intensity excursional data is discounted because exclusion of transitional data still leaves a bimodal distribution. No direct test has allowed us to rule out the idea that the observed pdf results from a mixture of two distinct distributions corresponding to two identifiable intensity states for the magnetic field. We investigate an alternative possibility that we were simply unable to recover a hypothetically smoother underlying distribution with a time span of only 1 Myr and the resolution of the current data set. Simulations from a stochastic model based on the geomagnetic field spectrum demonstrate that long period intensity variations can have a strong impact on the observed distributions and could plausibly explain the apparent bimodality. Our 0–1 Ma distribution of VADMs is consistent with that obtained for average relative paleointensity records derived from sediments. © 2008 Elsevier B.V. All rights reserved.