Magnetic charachterization of surface sediments in the South Atlantic

Surface sediment samples representative for the tropical and subtropical South Atlantic (15°N to 40°S) were investigated by isothermal magnetic methods to delineate magnetic mineral distribution patterns and to identify their predominant Holocene climatic and oceanographic controls. Individual parameters reveal distinct, yet frequently overlapping, regional sedimentation characteristics. A probabilistic ('fuzzy c-means') cluster analysis was applied to five concentration independent magnetic properties assessing magnetite to hematite ratios and diagnostic of bulk and fine-particle magnetite grain size and coercivity spectra. The resultant 10 cluster structures establish an oceanwide magnetic sediment classification scheme tracing the major terrigenous eolian and fluvial fluxes, authigenic biogenic magnetite accumulation in high-productivity areas, transport by ocean current systems, and effects of bottom water velocity on depositional regimes. Distinct dissimilarities in magnetic mineral inventories between the eastern and western basins of the South Atlantic reflect prominent contrasts of both oceanic and continental influences.

针对热带及亚热带南大西洋（15°N至40°S）区域的代表性表层沉积物样品，本研究采用等温磁学方法开展分析，以阐明磁性矿物的空间分布模式，并明确控制其分布的主要全新世气候与海洋学驱动因素。各单项磁学参数均展现出独特但时常相互重叠的区域沉积特征。本研究采用概率型模糊C均值（Fuzzy C-Means）聚类分析方法，对五种与浓度无关的磁学参数展开研究，这些参数可用于评估磁铁矿与赤铁矿的比值，同时可表征块状与细粒磁铁矿的晶粒尺寸及矫顽力谱特征。最终得到的10个聚类结构，构建了一套南大西洋洋盆全域的磁性沉积物分类方案，可追溯主要的陆源风成与河流输入通量、高生产力区域自生生物成因磁铁矿的富集过程、洋流系统的搬运作用，以及底层水流速对沉积环境的影响。南大西洋东西盆地间磁性矿物赋存特征的显著差异，反映了海洋与大陆双重影响的突出反差。