Collaborative Research: Sediment Nanomagnetism and Environmental Change: The Microbial Mineral Link

地球沉积物档案中留下的环境变化的矿物学和化学特征，提供了非常有价值的基线记录，可以成功地识别当前和未来的全球变化。 将这些定性测量转化为过去温度和降雨量的定量数值是全球环境变化研究的下一个主要挑战。 一种成功但定性的方法是利用透射电子显微镜（TEM）、电子发射损失光谱（EELS）和同步加速器X射线分析来观察环境敏感的羟基氧化铁微晶的变化，例如，扩展吸收精细结构（EXAFS） 然而，已经证明难以将这些结果从1-100 nm尺寸的单个纳米晶体与100 - 200 mg天然沉积物的等分试样相关联。 我们表明，一个多代理的方法，涉及整个样品的磁性和穆斯堡尔效应测量在低温（4.5K -300 K）和高磁场（3-5特斯拉），结合TEM/EELS/EXAFS研究合成纳米针铁矿，可以导致更精确的校准温度和Eh/pH值的矿物形成环境。 我们将扩大我们的研究到水铁矿，纳米赤铁矿和纳米磁铁矿。 特别是，异化铁还原菌（DIRB）将被确定从土壤剖面的田间实验，并在体外实验中作为培养的细菌，以确定如何过去的温度，降雨量，以及夏季生长季节的长度可以从磁性估计的纳米磁铁矿在现代土壤和古代土壤（古土壤）。 我们希望我们的研究将导致首次关于微生物（DIRB）在纳米磁铁矿矿化中的作用的对照实验，并寻找土壤中微生物纳米磁铁矿中的铁同位素特征。

Mineralogical and chemical signatures of environmental change, left behind in the earth's sediment archives, provide immensely valuable baseline records against which current and future global change an be successfully recognized. Conversion of these qualitative measures to quantitative numerical values of past temperatures and rainfall is the next major challenge in global environmental change research. One successful but qualitative approach has been to observe changes in environmentally sensitive iron oxyhydroxide microcrystals utilizing transmission electron microscopy (TEM), electron emission loss spectroscopy (EELS) and synchrotron x-ray analysis, e.g., extended absorption fine structure (EXAFS). However, it has proven difficult to relate these results from 1-100 nm-sized individual nanocrystals to 100 - 200 mg aliquots of natural sediments. We show that a multi-proxy approach involving whole sample magnetic and Mossbauer effect measurements at low temperatures (4.5K - 300K) and high magnetic fields (3-5 Tesla), combined with TEM/EELS/EXAFS studies of synthesized nanoparticles of goethite, can lead to more precise calibrations for temperature and Eh/pH of the mineral formation environment. We will expand our research into ferrihydrite, nanohematite and nanomagnetite. In particular, dissimilatory iron reducing bacteria (DIRB) will be identified from field experiments on soil profiles and also used as cultured bacteria in in vitro experiments to determine how past temperature, rainfall, and also the length of summer growing season can be obtained from magnetically estimated nanomagnetite in modern soils and ancient soils (paleosols). Our research, it is hoped, will lead to the first controlled experiments on the role of microbes (DIRB) in nanomagnetite mineralization, and a search for iron isotope signatures in microbial nanomagnetite in soils.