Collaborative Research: Magnetic Properties of Greenland and Antarctic Ice Cores

主要研究人员成功地测量了来自格陵兰NorthGRIP核心的不同气候间隔的冰样品中超细磁性颗粒的浓度，使用低温（77 K）等温剩余磁化（ESTA）分析，并将其与气溶胶尘埃的质量浓度进行了比较，其变化为10倍。 从冰期到间冰期，冰的平均强度变化为三倍，在间冰期较低。 磁性测量是可重复的，并且远高于在清洁实验室条件下制成的超纯水冰的磁性强度。冰样品的磁化率采集曲线与磁铁矿和辅助赤铁矿贡献的混合物相容，这是中国黄土高原原始黄土的典型磁性，被认为与格陵兰冰中的灰尘在东亚沙漠中具有相同的来源。 冰的磁化强度和总尘埃质量的比较显示出非常好的相关性，但也揭示了一个大的不相关的磁化，这是基本上恒定的不同的气候阶段，是在间隔非常低的测量尘埃浓度的主导成分。不相关的磁化可能是由于高磁性行星际尘埃粒子（IDP）的恒定通量或更普遍存在的超细颗粒气溶胶尘埃质量，在库尔特计数器测量中基本上没有检测到。 后者意味着冰期和间冰期之间的实际尘埃浓度对比要比估计的小得多。可以通过从南极洲的冰芯中获得比较数据来评估这些备选假设，南极洲的气溶胶尘埃通量与格陵兰截然不同（浓度、来源），而国内流离失所者的通量应该大致相同。主要研究人员将测量一套样品的磁化强度，这些样品代表了来自东方冰芯的冰川和间冰期尘埃浓度的全部范围。将使用能够在大样本（~50 cc）上产生2.5 T磁场的新脉冲磁化器，从12个不同气候间隔中的每个间隔中产生约10个样本的电磁波采集曲线，以实现饱和和高信号电平。使用库尔特计数器测量相同样品的粉尘浓度。将从North GRIP分析来自具有中等粉尘浓度的选定间隔的额外样本集，以巩固该区域的磁化与粉尘浓度曲线。将进行SEM-EDXRF分析以表征粉尘。 NorthGRIP和东方号之间的磁化与尘埃浓度关系的比较将使他们能够对来自外星粒子通量的不相关磁化的贡献进行定量估计，可能还有未检测到的气溶胶尘埃质量。这些新实验的结果预计将对我们理解尘埃在长期气候变化中的作用具有广泛的意义。

The Principal Investigators have successfully measured the concentration of ultra-fine magnetic particles in ice samples from different climatic intervals from the NorthGRIP core, Greenland, using low temperature (77K) isothermal remnant magnetization (IRM) analysis and compared it with the mass concentration of aerosol dust that varies by a factor of ten. The mean IRM intensity of the ice varies by a factor of three from glacial to interglacial intervals, being lower during interglacials. The magnetic measurements are reproducible and well above the IRM intensity of ultra-pure water ice made under clean lab conditions. The IRM acquisition curves of the ice samples are compatible with a mixture of magnetite and subsidiary hematite contributions, magnetic properties that are typical of pristine loess from the Chinese loess plateau, which is considered to have the same source in the eastern Asian deserts as dust in Greenland ice. Comparison of the IRM intensity and total dust mass of the ice shows a remarkably good correlation, but also reveals a large uncorrelated magnetization, which is essentially constant over the different climatic stages and is the dominant component during intervals with very low measured dust concentrations. The uncorrelated magnetization may be due to either a constant flux of highly magnetic interplanetary dust particles (IDPs) or the more general presence of ultrafine grain aerosol dust mass that were largely undetected in the Coulter Counter measurements. The latter would imply that the actual dust concentration contrast between glacial and interglacial intervals is much smaller than estimated. These alternative hypotheses can be evaluated by obtaining comparative data from ice cores from Antarctica, where the aerosol dust flux is radically different (concentration, source) than in Greenland whereas the flux of IDPs should be about the same. The Principal Investigators will measure the magnetization of a suite of samples representing the full range of glacial and interglacial dust concentrations from the Vostok ice core. IRM acquisition curves will be generated for about 10 samples from each of 12 distinct climatic intervals using a new pulse magnetizer capable of generating fields to 2.5 T on large (~50 cc) samples to achieve saturation and high signal level. Dust concentrations will be measured on the same samples using a Coulter Counter. Additional sets of samples from selected intervals with intermediate dust concentrations will be analyzed from North GRIP to solidify the magnetization vs. dust concentration curve from that region. SEM-EDXRF analyses will be done to characterize the dust. A comparison of the magnetization vs. dust concentration relationships between NorthGRIP and Vostok will allow them to make quantitative estimates of the contributions to the uncorrelated magnetization from the flux of extraterrestrial particles and possibly, the undetected aerosol dust mass. The outcome of these novel experiments is expected to have broad significance to our understanding of the role of dust in long-term climate change.