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

在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（例如扩展吸收精细结构（EXAFS））观察环境敏感的氢氧化铁微晶体的变化。然而，将这些1-100纳米大小的单个纳米晶体的结果与100 - 200毫克等分的天然沉积物联系起来已经证明是困难的。我们发现，在低温（4.5K - 300K）和高磁场（3-5特斯拉）下进行全样品磁性和穆斯堡尔效应测量的多代理方法，结合对合成针铁矿纳米颗粒的TEM/EELS/EXAFS研究，可以更精确地校准矿物形成环境的温度和Eh/pH。扩大对水合铁、纳米赤铁矿、纳米磁铁矿的研究。特别是，异化铁还原细菌（DIRB）将从土壤剖面的现场实验中识别出来，并在体外实验中用作培养细菌，以确定如何从现代土壤和古代土壤（古土壤）中的磁性估计纳米磁铁矿中获得过去的温度，降雨量和夏季生长季节的长度。我们的研究，希望将导致第一个关于微生物（DIRB）在纳米磁铁矿成矿作用的控制实验，并在土壤中微生物纳米磁铁矿中寻找铁同位素特征。

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.