Paleointensity of the geomagnetic field during the last 2.5 million years

自Brunhes年代（Sint-800）地磁叠加古强度记录建立以来，相对古强度的研究一直致力于获得上个年代的高分辨率记录。100 kyr，如NAPIS-75，并延长记录的年龄比Brunhes年代。这项研究的目的是澄清相对古强度变化，因为3马。对赤道西太平洋西加罗林海盆和南太平洋马尼希基海台的6个沉积岩芯进行了古地磁研究。这些岩心覆盖了最后1.2到3米。y.测量包括磁化率、自然回复磁化强度（NRM）、无滞后回复磁化强度（ARM）和等温回复磁化强度（NRM）。对u通道采集的样本进行反卷积，以提高时间分辨率。通过对NRM强度进行ARM归一化处理，估算了古地磁场的相对强度，并将磁化率和ARM与南海ODP 1143站的氧同位素曲线进行了对比，从而对沉积岩芯进行了年龄控制。部分颜色反射率用于相关性。对于一个核心，氧同位素比值进行了测量，并用于年龄估计。所有岩芯的相对古强度变化在年龄的不确定性（几万年）内一致。通过叠加这些记录与年龄的微小调整，我们建立了一个古强度曲线在过去的3米。y.变化的特点是准周期性发生的强度低整个记录，其中许多似乎对应于以前报告的地磁漂移或极性边界。这些特征与在Brunhes年代Sint-800记录中观察到的特征相似，但没有观察到“不对称的模式”。

Since the establishment of a stacked geomagnetic paleointensity record during the Brunhes Chron (Sint-800), researches on relative paleointensity have been directed to obtaining high-resolution records during the last ca. 100 kyr such as the NAPIS-75,and to extending records towards ages older than the Brunhes Chron. This study was aimed to clarify relative paleointensity variations since 3 Ma. A paleomagnetic study was conducted on six sediment cores obtained from the West Caroline Basin in the western equatorial Pacific and the Manihiki Plateau in the South Pacific. These cores cover the last 1.2 to 3 m. y. The measurements include magnetic susceptibility, natural remanent magnetization (NRM), anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM). Deconvolution was applied for samples taken by u-channels to increase time resolution. Relative paleointensity of the geomagnetic field was estimated from NRM intensity normalized by ARM. Age control of the sediment cores was performed mainly by correlating magnetic concentration changes (magnetic susceptibility and ARM) to the oxygen isotope curve of ODP Site 1143 in the South China Sea. Partly color reflectance was used for the correlation. For one core, oxygen isotope ratios were measured and used for the age estimation. Relative paleointensity variations of all cores agree well within uncertainty of age (a few tens of thousand years). By stacking these records with minor adjustments of ages, we have established a paleointensity curve during the last 3 m. y. The variations are characterized by quasi-periodic occurrence of intensity lows throughout the record, and many of them seem to correspond to previously reported geomagnetic excursions or polarity boundaries. These features are similar to those observed in the Sint-800 record during the Brunhes Chron. The "asymmetric sawtooth pattern" was not observed.