Age model of ODP Site 162-983

At ODP Site 983, relative geomagnetic paleointensity and planktic and benthic delta18O records have been acquired for the last 350 kyr. The mean sedimentation rate in this interval is 11.3 cm/kyr. Magnetic properties and hysteresis ratios indicate that pseudo-single domain magnetite is the remanence carrier. Volume susceptibility (kappa), anhysteretic (ARM) and isothermal (IRM) remanence values vary by a factor of 3-4, well within the criteria usually cited for paleointensity studies. Natural remanent magnetization (NRM) is normalized by ARM and IRM to acquire the paleointensity proxy. Arithmetic means of NRM/ARM and NRM/IRM, calculated for five demagnetization steps in the 25-45 mT range, constitute the relative paleointensity estimates. Some paleointensity lows (particularly those at ~40, ~120 and ~188 ka) are associated with directional excursions of the field, especially the event at ~188 ka (referred to here as the Iceland Basin Event) that constitutes a short-lived polarity reversal. For the last 200 kyr, the records can be correlated with other high-resolution paleointensity records such as those from the Labrador Sea, Mediterranean/Somali Basin and Sulu Sea, implying that the millennial scale features are globally synchronous. A labeling system for paleointensity features is proposed that ties prominent highs and lows to oxygen isotope stages.

在大洋钻探计划（Ocean Drilling Program, ODP）983站位，研究人员获取了过去35万年以来的相对地磁古强度、浮游有孔虫与底栖有孔虫δ¹⁸O（delta18O）记录。该沉积段的平均沉积速率为11.3厘米/千年。磁学参数与磁滞比值分析表明，假单畴（pseudo-single domain, PSD）磁铁矿是该沉积物的剩磁载体。体积磁化率（κ，kappa）、非滞剩磁（anhysteretic remanence, ARM）与等温剩磁（isothermal remanence, IRM）的数值波动幅度达3~4倍，完全符合古强度研究常用的判据范围。研究人员通过将天然剩磁（natural remanent magnetization, NRM）分别归一化至ARM与IRM，得到古强度替代指标。对25~45毫特斯拉（mT）区间内的5步退磁步骤计算NRM/ARM与NRM/IRM的算术平均值，以此作为相对古强度的估算值。部分古强度低值（尤其对应约40、120和188千年前的特征）与地磁场方向漂移事件相关，其中约188千年前的事件（本文称之为冰岛盆地事件）属于一次短暂的极性反转事件。针对过去20万年的时段，本站位的记录可与拉布拉多海、地中海/索马里海盆以及苏禄海等地的高分辨率古强度记录进行对比，这表明千年尺度的古强度特征具有全球同步性。本文提出了一套古强度特征的标记体系，将显著的古强度高低值与氧同位素阶绑定对应。