Paleoclimatic and orbital modulation of the geomagnetic field

1. 研究了海洋沉积物中磁性颗粒间的静磁相互作用强度。在相对古强度估计上，由于静磁作用对沉积物NRM采集效率的影响较大，IRM对NRM采集效率的正一化优于ARM。我们在西北太平洋构造了近250年来的古强度叠加。为了获得可靠的相对古强度记录，必须排除早期成岩作用导致磁性矿物溶解的层位。s比代表了低矫顽力磁性矿物的比例，对磁铁矿的溶解很敏感，因此可以用来探测这类水平。我们从北太平洋的沉积物岩心中获得了最近1.6万年的相对古强度记录。并与西赤道太平洋地核的古强度和磁性进行了对比。两个地区的相对古强度吻合较好，但磁性差异很大。利用小波变换进行的时间序列分析表明，古强度记录包含100 kyr时间尺度的变化。磁性能的变化与古强度的变化并不同步，即使在100 kyr的共同时间尺度上，两者之间也没有显著的相关性。因此，我们认为古强度记录的100-kyr变化是地磁成因的，而不是由古气候变化引起的沉积物磁性变化引起的。在赤道东印度洋（EEI）的岩心中恢复了近800 kyr的古强度和倾角变化。赤道西太平洋（WEP）的大倾角异常区域并没有延伸到印度洋。较弱的偶极子场导致持续的非偶极子分量相对贡献较大的长期倾角变化模式得到了支持。少

1. We investigated the strength of magnetostatic interaction among magnetic particles in marine sediments. On relative paleointensity estimation, IRM is preferable to ARM for normalizing difference in NRM acquisition efficiency of sediments because ARM acquisition is strongly affected by the magnetostatic interaction.2. We constructed a paleointensity stack during the last 250 kyr in the Northwest Pacific. To obtain reliable relative paleointensity records, it is necessary to exclude horizons that suffer from dissolution of magnetic minerals owing to early diagenesis. The S-ratio, which represents a proportion of low coercivity magnetic minerals, is sensitive to magnetite dissolution, and thus can be used for detecting such horizons.3. We obtained a relative paleointensity record during the last 1.6 m.y. from a sediment core in the North Pacific. The paleointensity and magnetic properties of this core were compared with those from the western equatorial Pacific. Relative paleointensiti … More es of the two areas coincide well, whereas magnetic properties differ greatly. A time-series analysis using a wavelet transform showed that paleointensity records contain variations with a time scale of 100 kyr. Variations of magnetic properties are not synchronous with those of paleointensity, and there is no significant correlation between the two even if they have a common time scale of 100 kyr. We thus conclude that the 100-kyr variations in paleointensity records are of geomagnetic origin, and not caused by magnetic property variations of sediments induced by paleoclimate changes.4. Paleointensity and inclination variations during the last 800 kyr were recovered from cores in the eastern equatorial Indian Ocean (EEI). The area of a large inclination anomaly in the western equatorial Pacific (WEP) does not extend to the Indian Ocean. The model of long-term inclination variations that a weaker dipole field causes a larger relative contribution of persistent non-dipole components is supported. Less