(Table 2) U-channel paleomagnetic record of ODP Site 178-1098

Thick Holocene sedimentary sections (>45 m) cored in the Palmer Deep by the United States Antarctic Program (USAP) and during Ocean Drilling Program (ODP) Leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes. After removal of a low-coercivity drilling overprint the sediments display a stable, single-component remanent magnetization. Two short cores that recovered the uppermost 2.6 m of sediment have inclinations that fluctuate about the present day inclination (-57°) measured at Faraday Station, and several features with wavelengths of 10 to 20 cm appear to be correlative. However, shipboard measurements of inclination fluctuations on split-core samples from three holes drilled at ODP Site 1098 do not correlate well with each other, even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole (GAD) inclination. The correlation is improved dramatically by using inclinations measured on u-channels taken from the pristine center of a split core. Consequently, the anomalous directions and the resulting poor between-hole correlation of inclinations obtained from shipboard data can be attributed to coring-induced deformation, which is common on the outer edge of ODP piston cores, and/or measurement artifacts in the split-core data. Our preferred inclination record is thus derived from u-channel results. The upper ~25 m represents continuous sedimentation over the past 9000 yr, with an average sedimentation rate exceeding 250 cm/kyr (0.25 cm/yr). Given that remanence measurements on u-channels average over an interval <7 cm long, we obtained independent measurements of the paleo-geomagnetic field that average over only ~30 yr. This high-resolution record is characterized by an inclination that fluctuates within +/-15° of the current GAD inclination.

美国南极计划（United States Antarctic Program, USAP）与大洋钻探计划（Ocean Drilling Program, ODP）第178航次在帕默海槽（Palmer Deep）获取的厚层全新世沉积剖面（厚度超过45米），为研究南极高纬度地区的古地磁场演化行为提供了首个契机。经移除低矫顽力钻井叠磁化后，沉积物呈现出稳定的单分量剩磁特征。两根采集了表层2.6米沉积物的短岩芯，其地磁倾角围绕法拉第站（Faraday Station）实测的现今地磁倾角（-57°）波动，且若干波长为10至20厘米的异常特征具有可对比性。然而，对大洋钻探计划1098站位（ODP Site 1098）三个钻孔的劈分岩芯样品进行的船上倾角波动测量结果却彼此相关性较差；尽管强度与磁化率数据的相关性极佳，且各钻孔岩芯的平均倾角均与预期的地心轴向偶极子（geocentric axial dipole, GAD）倾角相符。若采用从劈分岩芯的原始中心部位获取的U型岩芯（u-channels）测得的倾角数据，则相关性可得到显著提升。据此，由船上测量数据得到的异常地磁方向以及由此导致的各钻孔间倾角相关性差的问题，可归因于取芯过程引发的变形（该现象在大洋钻探计划活塞岩芯的外缘部位极为常见）以及/或劈分岩芯数据中的测量伪影。因此，本研究优先采用U型岩芯测量结果构建倾角记录。该记录的上部约25米对应了过去9000年的连续沉积，平均沉积速率超过250厘米/千年（0.25厘米/年）。由于U型岩芯的剩磁测量是在长度小于7厘米的区间内取平均，因此我们获得的古地磁场独立测量结果的时间平均跨度仅约30年。该高分辨率记录的特征为：倾角在当前GAD倾角的±15°范围内波动。