Fast geomagnetic field variations recorded in glacial Black Sea sediments
Authors: Nowaczyk Norbert , Liu Jiabo , Arz Helge 
Published: March 2020

&lt;p align=&quot;justify&quot;&gt;&lt;span&gt;&lt;tt class=&quot;western&quot;&gt;Over the last 12 years, &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;from &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;m&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;agnetostratigraphic investigation of 16 sediment cores from the Southeastern Black Sea, &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;a &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;high-resolution paleo-secular variation record spanning from 64 to 14 ka &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;could be compiled&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;Due to glacial erosion in the catchment sedimentation rates are in the range of 25 to 50 cm/kyr. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;Obtained relative paleointensity data reflect a highly dynamic geomagnetic field during that time. By comparison to absolute paleointensity data it could be &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;estimat&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;ed that the field intensity varied between about 3 &amp;#181;T and &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;60 &amp;#181;T &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;(present day field intensity 48 &amp;#181;T)&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;. The lowest value is associated with the Laschamps polarity excursion &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;centred &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;at 41.&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;0&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt; ka. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;Its&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt; N-R and R-N transitions lasted just 200 and 270 years, respectively, &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;with a 440 year long stable reversed phase &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;(&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;intensity &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;max. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;12 &amp;#181;T, &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;VGP latitudes higher than 65&amp;#176;S) &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;in between&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;The second deepest intensity minimum at 64.5 ka with about &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;8&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt; &amp;#181;T is associated with fast directional changes but still in the range of normal secular variation (VGP latitudes above 45 &amp;#176;N). &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;This is likely the mid-latitude expression of the postulated Norwegian-Greenland Sea excursion, as derived from Arctic marine sediments. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;In contrast to this, the Mono Lake excursion at 34.5 ka was characterized by intermediate field in&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;t&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;ensities &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;of 20 &amp;#181;T, but clearly non-dipolar directional variation&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;s&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;, indicating a multi-polar field configuration &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;during the excursion&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;A&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;nother&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt; moderate field minimum of 25 &amp;#181;T at 18.5 ka is coeval with the postulated Hilina Pali excursion. But, despite high sedimentation rates (&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;50 cm/kyr&lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;), only normal secular variation amplitudes were recorded in Black Sea sediments with VGP latitudes higher than 60&amp;#176;N. &lt;/tt&gt;&lt;tt class=&quot;western&quot;&gt;Ongoing re-sedimentation experiments with Black Sea mud indicate a very rapid lock-in of the paleomagnetic signal and a fairly linear relationship between field strength (1.8 to 110 &amp;#181;T) and acquired magnetization. Thus it can be concluded that data from Black Sea sediments reflect true geomagnetic field behaviour. &lt;/tt&gt;&lt;/span&gt;&lt;/p&gt;