Collaborative Research: Magnetic characterization of dust in Greenland Ice

这是Lamont-Doherty地球天文台和罗格斯大学的合作提案。对格陵兰岛全新世（间冰期）和末次盛冰期（LGM）样品的磁性进行了测试。冰的主要抗磁性阻碍了对磁化率的有用测量，但样品中含有足够浓度的氧化铁磁性矿物，可以使用等温剩余磁化（IRM）强度来估计。为了获得可靠的测量结果，必须解决一些不寻常的问题。格陵兰冰样品的矫顽力谱与主要的磁铁矿载体相一致。初步磁数据的一个不寻常的方面是，尽管LGM冰通常比间冰期冰含有更高浓度的风成尘，但LGM冰样品的IRM值往往低于间冰期冰样品。磁性矿物仅占风运尘埃的一小部分，但可能反映了源地区的成土作用和其他环境条件的变化，以及可能的源地区和/或大气环流和运输的差异。推测其源区为东亚，现为塔克拉玛干等内蒙古、蒙古沙漠，也是中国黄土高原沉积物的源区。本研究的目的是通过对冰磁数据与粉尘提取物的直接测量来验证冰磁测量方法，并将格陵兰冰中极地粉尘的磁性与可能的来源地区（如中国黄土和沙漠沉积物）的磁性进行比较。这些数据将使我们能够评估使用磁性作为格陵兰尘埃的独立来源示踪剂的可行性，并增加我们对造成冰和黄土沉积物磁性的深刻古气候依赖变化的过程的理解。

AbstractKentOPP-01-18470BiscayeOPP-01-18458This is a collaborative proposal between Lamont-Doherty Earth Observatory and Rutgers University. The magnetic properties of Greenland ice were tested in samples of Holocene (interglacial) and Last Glacial Maximum (LGM) age. The dominant diamagnetism of ice prevented useful measurements of magnetic susceptibility, but the samples contain a sufficient concentration of iron oxide magnetic minerals that can be estimated using isothermal remanent magnetization (IRM) intensity. Some unusual problems had to be solved in order to obtain reliable measurements. Coercivity spectra in the Greenland ice samples are consistent with a dominant magnetite carrier. An unusual aspect of the preliminary magnetic data is that the LGM ice samples tend to have lower IRM values than interglacial ice samples, although LGM ice generally contains much higher concentrations of eolian dust than interglacial ice. The magnetic minerals constitute only a small fraction of the wind transported dust, but may reflect variations in pedogenesis and other environmental conditions in the source area(s), as well as differences in the possible source areas and/or atmospheric circulation and transport. The source area is presumed to be eastern Asia, and is presently the Takla Makan and other Inner Mongolian and Mongolian deserts, which were also the source areas for the sediments of the Chinese Loess Plateau. The objectives of this research are to validate a methodology of ice magnetic measurements by calibrating the ice magnetic data with direct measurements of dust extracts, and to compare the magnetic properties of polar dust in Greenland ice with those of possible source area(s), such as Chinese loess and desert sediments. These data will allow us to assess the feasibility of using magnetic properties as an independent provenance tracer of Greenland dust and to increase our understanding of the processes responsible for the profound paleoclimatically-dependent variations in magnetic properties of ice and loess deposits.