Marine magnetic anomalies as recorders of geomagnetic intensity variations
Marine magnetic anomalies as recorders of geomagnetic intensity variations
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DOI：
10.1016/s0012-821x(96)00184-7
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发表时间：
1996-11
影响因子：
5.3
通讯作者：
J. Gee;D. Schneider;D. Kent
中科院分区：
文献类型：
--
作者：
J. Gee;D. Schneider;D. Kent
除了提供过去地磁极性反转的可靠记录外，海洋磁异常通常显示较短的波长变化，这可能提供在恒定极性间隔内地磁强度变化的信息。为了评价这种可能的地磁信号，我们将中央异常的海面剖面与深海沉积物的Brunhes年龄（0-0.78 Ma）古强度记录合成的剖面进行了比较。合成剖面与超快速扩张东太平洋南隆起观测剖面的相似性表明，地磁强度变化在洋壳磁化过程中起重要作用。这种解释进一步得到了中央异常模式在缓慢扩张脊上的系统变化的支持，这与沉积物衍生的古强度的逐渐平滑的记录完全一致。如果沉积记录与现有的绝对古强度数据进行校准，准确地记录了布伦内斯的偶极子强度变化，那么可以得出，大部分布伦内斯的地磁强度要么低于过去10 ka的平均偶极矩，要么低于0.05 ~ 5.0 Ma的平均值。此外，沉积物古强度记录反映了地磁强度的显著增加，从40 ka附近的~ 2 × 1022Am2的低点到~ 3 ka的峰值（11 × 1022Am2），这已经从绝对古强度测定中得到了很好的证明。我们认为，地磁强度的变化可能是震源层磁化强度快速变化和由此产生的中央磁高异常的最重要原因。
In addition to providing a robust record of past geomagnetic polarity reversals, marine magnetic anomalies often show shorter wavelength variations, which may provide information on geomagnetic intensity variations within intervals of constant polarity. To evaluate this possible geomagnetic signal, we compare sea surface profiles of the Central Anomaly with synthetic profiles based on Brunhes age (0-0.78 Ma) paleointensity records derived from deep sea sediments. The similarity of the synthetic profiles and observed profiles from the ultra-fast spreading southern East Pacific Rise suggests that geomagnetic intensity variations play an important role in the magnetization of the oceanic crust. This interpretation is further supported by systematic variations in the pattern of the Central Anomaly at slower spreading ridges, which are entirely consistent with a progressively smoother record of the sediment-derived paleointensity. If the sedimentary records, as calibrated to available absolute paleointensity data, accurately record variations in dipole intensity over the Brunhes, it follows that much of the Brunhes was characterized by geomagnetic intensities lower than either the mean dipole moment for the past 10 ka or the average for the period from 0.05 to 5.0 Ma. Furthermore, the sediment paleointensity records reflect the significant increase in geomagnetic intensity, from a low of ∼ 2 × 1022Am2near 40 ka to a peak value (11 × 1022Am2) at ∼ 3 ka, that has been well documented from absolute paleointensity determinations. We suggest that geomagnetic intensity variations may be the most important cause of the rapid changes in the source layer magnetization near the ridge crest and the resultant Central Anomaly Magnetic High.