Towards the Development of Magnetic Provenance Tracers in Antarctic Glacial Marine Sediments: A Pilot Study in the Antarctic Peninsula Region.

该奖项由极地方案办公室南极地质和地球物理方案提供，为一项初步研究提供资金，该研究旨在测试利用岩石磁性作为南极冰川海洋沉积物的沉积物来源示踪剂的潜力。一种追踪沉积物来源的方法将能够更有意义地解释沉积物岩心中记录的运输和沉积过程。可以想见的是，人们可以确定大陆冰盖的哪些部分正在推进和供应，或者正在解体，以形成残骸满载的冰山。可以想象，人们可以追踪携带着IRD的护堤的古水流，或者识别携带风沙物质的风型。岩石磁学方法具有价格便宜、快速、使用高灵敏度仪器进行无损分析的优势，能够处理少量物质。选择的测试区域是南极半岛(AP)地区。鉴于最近的变暖趋势、冰架的解体以及目前正在发生的快速生态和物理变化，AP地区是古气候-全球变化界强烈关注的主题。AP地区的构造背景和岩石学得到了广泛的研究，该地区是正在进行的海洋地质和LTER研究的地点。伯德极地研究中心存放着来自主要岩石类型(以及支持已发表的岩石学和化学数据)的数千个预先存在的样本，可供研究。岩石磁法提供了一种快速、灵敏、廉价的手段来识别岩石和沉积物中的含铁矿物。该项目将系统地调查南极半岛上暴露的主要基岩建造的材料性质和磁性，以及选定的地表和历史沉积物样本。开发可靠的磁性物源示踪剂的步骤是：o通过沉积物的材料性质，如精确的化学成分、氧化参数、晶格参数和颗粒形态，自信地将沉积物与其来源物质联系起来；o确定是否可以使用独特的磁性特征来确定这些材料性质；o测试是否可以在沉积物中识别磁性特征，从而提供一种岩石磁学手段来追踪沉积物，追溯到其来源岩石；o利用现有的岩石学和化学数据，验证磁法的成功；来自Graham Land的花岗岩和沉积物中含有磁铁矿、钛磁铁矿和赤铁矿。初步研究表明，AP岩中的磁铁矿和钛磁铁矿颗粒受到不同程度的氧化和杂质含量的影响，从而产生了可重现的、可测量的磁性特征。所有的磁铁矿都不一样。即使金属氧化学计量比的微小偏差和阳离子分布的偏差也会对金属氧化物的物理和磁性产生很大影响。这就是提出磁性方法可能是有效示踪剂的基础。任何单一的磁性参数都不足以唯一地表征样品，也不足以作为沉积物和源岩之间的纽带。因此，通过遵循上面概述的步骤，希望可以建立基于可量化材料属性的联系，然后可以确定这些属性的磁性特征。这项工作将检验磁性参数组合可用于识别材料属性的概念。如果能够证明沉积物中独特的磁性可以指示物质的状态，并且这些状态可以与它们的母质相匹配，那么岩石磁性可能提供一种快速、廉价的手段来追踪沉积物的来源。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a pilot study designed to test the potential of using rock magnetic properties as sediment provenance tracers for Antarctic glacial marine sediment. A means of tracing sediment provenance would enable more meaningful interpretation of transport and depositional processes recorded in sediment cores. One could conceivably determine which parts of the continental ice sheet were advancing and supplying till, or disintegrating to create debris-laden icebergs. One could conceivably trace the paleocurrents that carried IRD-laden bergs, or identify wind patterns that carried the eolian material. Rock magnetic methods have the advantage of being inexpensive, rapid, non-destructive analyses using highly sensitive instrumentation capable of working with small amounts of material.The chosen test area is the Antarctic Peninsula (AP) region. The AP region is the subject of intense interest to the paleoclimate-global change community in light of the recent warming trend, disintegration of ice shelves, and rapid ecological and physical changes presently taking place. The tectonic setting and petrology of the AP region have been studied extensively, and this region is site of on-going marine geology and LTER research. Thousands of pre-existing samples from the major rock types (and supporting published petrologic and chemical data) are housed at the Byrd Polar Research Center and are available for study.Rock magnetic methods provide a rapid, sensitive, inexpensive means of identifying iron-bearing minerals in rocks and sediment. This project will systematically investigate the material properties and magnetic properties of the major bedrock formations exposed on the Antarctic Peninsula along with selected surface and historic sediment samples. The steps in developing reliable magnetic provenance tracers are:o Confidently linking sediments with their source materials via their materials properties such as precise chemical composition, oxidation parameter, lattice parameter, and grain morphologyo Determining if a unique magnetic signature can be used to identify those material propertieso Testing if the magnetic signature is recognizable in the sediment, thus providing a rock magnetic means of tracing sediments back to their source rockso Verifying the success of the magnetic method by using existing petrologic and chemical dataIgneous rocks and sediment from Graham Land contain magnetite, titanomagnetite, and hematite. Initial studies indicate that the magnetite and titanomagnetite grains in the AP rocks are affected by varying degrees of oxidation and impurity content, which generates a reproducible, measurable magnetic signature. All magnetite is not the same. Even small deviations from metal-oxygen stoichiometry and deviations in cation distributions can have large effects on the physical and magnetic properties of metal oxides. This is the basis for suggesting that magnetic methods may be effective tracers. No single magnetic parameter is sufficient to uniquely characterize a sample or to serve as a link between sediment and source rock. Therefore, by following the steps outlined above it is hoped that a link based on quantifiable material properties can be established, and then magnetic signature of those properties can be determined. This work will test the concept that combinations of magnetic parameters can be used to identify material properties. If it can be demonstrated that distinctive magnetic properties in sediments are indicative of material states, and these states can be matched with their parent material, then rock magnetism may provide a rapid, inexpensive means of tracing sediment provenance.