Maxbauer Daniel P, Feinberg Joshua M, Fox David L, Nater Edward A
Institute for Rock Magnetism, University of Minnesota, Minneapolis, MN, 55455, USA.
Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA.
Sci Rep. 2017 Dec 14;7(1):17575. doi: 10.1038/s41598-017-17722-2.
Pedogenesis produces fine-grained magnetic minerals that record important information about the ambient climatic conditions present during soil formation. Yet, differentiating the compounding effects of non-climate soil forming factors is a nontrivial challenge that must be overcome to establish soil magnetism as a trusted paleoenvironmental tool. Here, we isolate the influence of vegetation by investigating magnetic properties of soils developing under uniform climate, topography, and parent material but changing vegetation along the forest-prairie ecotone in NW Minnesota. Greater absolute magnetic enhancement in prairie soils is related to some combination of increased production of pedogenic magnetite in prairie soils, increased deposition of detrital magnetite in prairies from eolian processes, or increased dissolution of fine-grained magnetite in forest soils due to increased soil moisture and lower pH. Yet, grain-size specific magnetic properties associated with pedogenesis, for example relative frequency dependence of susceptibility and the ratio of anhysteretic to isothermal remanent magnetization, are insensitive to changing vegetation. Further, quantitative unmixing methods support a fraction of fine-grained pedogenic magnetite that is highly consistent. Together, our findings support climate as a primary control on magnetite production in soils, while demonstrating how careful decomposition of bulk magnetic properties is necessary for proper interpretation of environmental magnetic data.
成土作用会产生细粒磁性矿物，这些矿物记录了土壤形成过程中存在的周围气候条件的重要信息。然而，区分非气候性土壤形成因素的复合效应是一项艰巨的挑战，要将土壤磁性确立为一种可靠的古环境工具，就必须克服这一挑战。在这里，我们通过研究在明尼苏达州西北部森林 - 草原交错带气候、地形和母质均一但植被变化的情况下发育的土壤的磁性特性，来分离植被的影响。草原土壤中更大的绝对磁增强与草原土壤中自生磁铁矿产量增加、风成过程中草原碎屑磁铁矿沉积增加，或者森林土壤中由于土壤湿度增加和pH值降低导致细粒磁铁矿溶解增加的某种组合有关。然而，与成土作用相关的粒度特定磁性特性，例如磁化率的相对频率依赖性以及非滞磁性与等温剩磁的比率，对植被变化不敏感。此外，定量解混方法支持一部分高度一致的细粒自生磁铁矿。总之，我们的研究结果支持气候是土壤中磁铁矿产生的主要控制因素，同时表明对于正确解释环境磁数据而言，仔细分解总体磁性特性是必要的。
