Grain-size distribution and grain-size dependent magnetic susceptibility of sediment core GeoB18530-1

Since the weight percentages of (classifiable) IRD particles > 1 mm and (unclassifiable, but separable) IRD particles > 125 µm both largely underestimate the total content and magnetic impact of IRD, it is important to quantify also the finer IRD fractions and their magnetic susceptibilities. From each of the IRD-rich sediment units H1, I1 and H2, six magnetic cube samples of 6.2 cm³ each were combined, dried, weighed and ultrasonically suspended in water. These three slurries were successively washed through 16 stacked sieves with mesh sizes in approximately 0.5 phi steps from 4000 µm to 5 µm using a Fritsch wet sieve shaker. The sieve fractions were carefully collected, dried, weighed and measured in a Kappabridge KLY2 susceptometer. The data and therefrom-derived partial susceptibilities and cumulative distributions clearly demonstrate that the magnetically most dominant and "volatile" sediment particles fall into the 40-125 µm range. […]

鉴于1毫米以上（可分类的）内部反应沉积物颗粒和125微米以上（不可分类但可分离的）内部反应沉积物颗粒的重量百分比均大大低估了内部反应沉积物的总含量和磁影响，因此量化更细的内部反应沉积物组分及其磁化率显得尤为重要。从富含内部反应沉积物的沉积单元H1、I1和H2中，各选取了六个体积为6.2立方厘米的磁性立方体样本，经过干燥、称重后，采用超声波悬浮于水中。这三个悬浮液依次通过16层堆叠的筛网，筛网孔径以约0.5 phi的步长从4000微米到5微米不等，使用Fritsch湿筛摇床进行处理。筛分出的各部分样本被精心收集、干燥、称重并在Kappabridge KLY2磁化率仪上进行测量。所得数据及其由此派生的部分磁化率和累积分布清晰地表明，磁化率最高且‘易挥发’的沉积物颗粒主要分布在40至125微米的范围内。