Collaborative Research: Magnetic Properties of Greenland and Antarctic Ice Cores

首席研究人员使用低温(77K)等温剩余磁化(IRM)分析成功地测量了格陵兰NorthGRIP岩心不同气候间隔的冰样中超细磁性粒子的浓度，并将其与气溶胶尘埃的质量浓度进行了比较，气溶胶尘埃的质量浓度变化了十倍。从冰期到间冰期，冰的平均IRM强度变化了三倍，在间冰期较低。磁性测量是可重复性的，远远高于在干净的实验室条件下制作的超纯水冰的IRM强度。冰样的IRM采集曲线与磁铁矿和辅助赤铁矿的混合物相容，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尘埃具有相同的东亚沙漠来源。IRM强度与冰层总尘埃质量的比较显示出非常好的相关性，但也显示出很大的不相关磁化强度，在不同气候阶段基本上是恒定的，在测量到的尘埃浓度很低的时段是主要成分。这种不相关的磁化可能是由于高磁行星际尘埃粒子(IDP)的恒定磁通量，或者是更普遍地存在着库尔特计数器测量中基本上没有探测到的超细颗粒气溶胶尘埃质量。后者意味着冰期和间冰期之间的实际尘埃浓度对比比估计的要小得多。可以通过从南极洲冰芯获得比较数据来评估这些替代假设，南极洲的气溶胶粉尘通量(浓度、来源)与格陵兰岛完全不同，而境内流离失所者的通量应该大致相同。首席调查人员将测量一套样品的磁化程度，这些样品代表了来自沃斯托克冰芯的冰川和间冰期尘埃浓度的全部范围。IRM采集曲线将使用一种新型脉冲充磁器，从12个不同的气候间隔中的每个间隔产生约10个样品，该装置能够在大样本(~50毫升)上产生2.5T的磁场，以实现饱和和高信号电平。粉尘浓度将在相同的样本上使用库尔特计数器进行测量。来自选定区间的中等粉尘浓度的额外样品集将从North GRIP进行分析，以固化该区域的磁化强度与粉尘浓度的关系曲线。将进行SEM-EDXRF分析以表征粉尘。对NorthGRIP和Vostok的磁化强度与尘埃浓度之间的关系进行比较，将使他们能够对地外粒子通量以及可能未检测到的气溶胶尘埃质量对不相关磁化强度的贡献做出定量估计。这些新颖的实验结果有望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.