南极菲尔德斯半岛西海岸海滩沉积物环境磁学特征及其控制因素

Environmental magnetic characteristics and influencing factors on the west coast of Fildes Peninsula, Antarctica

南极无冰区独特的环境系统近几十年来被广泛地关注和研究,同时环境磁学方法在环境变化研究中也被越来越多的应用。本文通过对2015年采自南极菲尔德斯半岛西海岸一根长26 cm的柱样进行环境磁学、粒度、^(210)Pb和稳定碳同位素测试分析发现,由于海岸基岩为安山质玄武岩,所以沉积柱样整体的磁性矿物含量较高,表现出较强的磁性,其磁化率均值(χ_(lf))高达1 597×10^(-8) m^(3)·kg^(-1),约为一般海滩磁化率值的3~4倍。其磁性矿物类型主要是假单畴的亚铁磁性矿物颗粒(磁铁矿)且含有少量的反铁磁性矿物颗粒(赤铁矿)。垂向上^(210)Pb和粒度结果显示,柱样上段沉积物粒度较细,水动力较弱使得细粒磁性矿物颗粒被快速保存下来,而随着深度的增加粒度逐渐变粗,岸滩水动力相对增强,而且底部受到生物有机质溶解作用的影响导致柱样上段磁学参数值高于下段。

The unique environmental system of the Antarctic ice-free region has been widely studied in recent decades,and environmental magnetism is doubtlessly the method most commonly used in the study.In the year of 2015,a 26 cm long core was collected by the authors from the west coast of the Antarctic peninsula for environmental magnetism,granularity,^(210)Pb and stable carbon isotope testing and analysis.The bedrock of the coast is dominated by andesitic basalt,so the sediments of the core samples are high in magnetic minerals in general,that resulted in high magnetism.The average susceptibility(χlf)is about 1597×10^(-8)m^(3)·kg^(-1),almost 3~4 times higher than the beach magnetic susceptibility.The magnetic minerals mainly consist of ferromagnetic particles(magnetite)with small amount of antiferromagnetic particles(hematite).The vertical changes in^(210)Pb and granularity data suggest that the sediment particle size is too fine for water movement,and therefore,the movement of pore water is weak.Under such a circumstance,the fine magnetic mineral grains are easily to be preserved.With the increase in depth,the sediments gradually become coarser,and the movement of water is thus enhanced.Plus the influence of biological organic dissolution,magnetism parameters of the lower part of the core is decreased accordingly.