A Test of Paleomagnetic Field Variability at Equatorial Latitudes

地球磁场长期变化（PSV，包括方向和古强度）的古地磁研究需要了解其时空变化模式。目前，我们在赤道地区没有近3000年以前的PSV详细记录。然而，为了正确地解释其他纬度的PSV记录，并对地球深部可能的发电机源做出预测，最近的几个场变率模型需要了解赤道PSV。这项提议有五个科学目标。(1)从印度尼西亚/菲律宾赤道纬度恢复了两个重复的深海沉积物PSV记录（包括方向和古强度），这些记录历时13万年；(2)对所有沉积物进行了仔细的岩石磁研究（磁矿物学，ARM， IRM， CHI，加上选定的AMS和滞后测量），以评估环境影响可能对方向或古强度数据产生偏差的地方；(3)对最终的PSV记录进行详细的统计研究，重点关注（几乎全部）与四极子族发电机源相关的矢量和VGP角色散的时间变率；(4)对从贝加尔湖（俄罗斯）到Pounui湖（新西兰）的所有全新世PSV记录进行比较，包括本研究的新记录；(5)将这些岩心的Laschamp和Blake漂移时间间隔的PSV记录与北大西洋类似的PSV记录进行比较。最终的古地磁数据集将在PI的网站（http://earth.usc.edu/~slund）上提供。研究人员先前的工作表明，他们可以从赤道印度尼西亚/菲律宾地区的几个深海岩心中恢复过去13万年的高分辨率PSV记录（包括方向和古强度）。他们的初步PSV数据表明，低古强时期在赤道和高纬度波段都有较高的PSV角频散，但在赤道纬度的相对频散增加明显更大。假设四谱谱族色散水平作为纬度的函数是恒定的，那么在拉尚漂移期间，发电机源的四谱谱族可能是中纬度PSV色散的唯一原因！他们还发现了一个与拉尚漫游时间相当的旅行记录。将这一记录与来自中纬度北大西洋的拉尚漫游的详细记录进行比较，我们发现地球两侧的漫游在年龄上几乎是相同的。这两个区域都具有一类漂移的波形特征，但北大西洋Laschamp漂移有两个顺时针圈的漂移VGPs周期，而赤道漂移有两个逆时针圈的漂移VGPs周期。将提出的赤道PSV记录与其他纬度带的数据进行仔细比较，应该会对磁场变异性和引起磁场变异性的发电机过程提供重要的新见解。

Lund 0106685 Paleomagnetic studies of the Earth' magnetic field secular variation (PSV, both directions and paleointensity) require knowledge of its spatial and temporal pattern of variability. At present, we have no detailed PSV records in Equatorial regions prior to the last 3000 years. Yet, several recent models of field variability require an understanding of Equatorial PSV in order to properly interpret PSV records at other latitudes and make predictions about possible dynamo sources in the Earth's deep interior. This proposal has five scientific goals. (1) recover two replicate deep-sea sediment PSV records (both directions and paleointensity) spanning the last 130,000 years from Equatorial latitudes in Indonesia/Philippines, (2) carry out a careful rock magnetic study of all sediments (magnetic mineralogy, ARM, IRM, CHI, plus selected AMS and hysteresis measurements) to assess where environmental effects might be biasing the directional or paleointensity data, (3) carry out a detailed statistical study of the final PSV records focussing on the temporal variability of vector and VGP angular dispersion associated (almost entirely) with quadrapole-family dynamo sources, (4) carry out a comparison of all Holocene PSV records extending from Lake Baikal (Russia) to Lake Pounui (New Zealand) including the new records from this study, (5) compare the PSV records of the Laschamp and Blake excursion time intervals in these cores with similar PSV records from the North Atlantic Ocean. Final paleomagnetic datasets will be available on the PI's website (http://earth.usc.edu/~slund). The investigators' previous work indicates that they can recover high-resolution PSV records (both directions and paleointensity) for the last 130,000 years from several deep-sea cores in the Equatorial Indonesia/Philippines region. Their preliminary PSV data suggest that times of low paleointensity have higher PSV angular dispersion in both Equatorial and higher-latitude bands, but the relative increase in dispersion at Equatorial latitudes appears to be significantly greater. Assuming that the quadrapole-family dispersion level is constant as a function of latitude, it could be that the quadrapole family of dynamo sources is the sole cause of PSV dispersion at mid latitudes during the Laschamp excursion! They have also recovered an excursion record equivalent in time to the Laschamp Excursion. Comparison of this record with detailed Laschamp Excursion records from the mid-latitude North Atlantic Ocean suggests that the excursions on opposite sides of the Earth are virtually identical in age. Both regions have waveform characteristics of Class I excursions, but the Laschamp excursion in the North Atlantic Ocean has two cycles of clockwise-looping excursional VGPs while the Equatorial excursion has two cycles of counterclockwise-looping excursional VGPs. Careful comparisons of the proposed Equatorial PSV records with data from other latitude bands should provide significant new insight into magnetic field variability and dynamo processes that cause it.