Collaborative Research: Magnetic Properties of Greenland and Antarctic Ice Cores

合作研究：格陵兰岛和南极冰芯的磁性

• 批准号: 0424931
• 负责人: Pierre Biscaye
• 金额: $ 8.05万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-09-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0424931&HistoricalAwards=false
• 关键词: Collaborative; Research; Magnetic; Properties; Greenland

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.

主要研究人员使用低温（77K）等温残余磁化（IRM）分析，成功地测量了来自格陵兰岛NorthGRIP核心不同气候间隔的冰样品中超细磁颗粒的浓度，并将其与气溶胶粉尘的质量浓度进行了比较，气溶胶粉尘的质量浓度变化了十倍。从冰期到间冰期，冰的平均IRM强度变化为3倍，间冰期较低。磁测量是可重复的，远高于在干净的实验室条件下制造的超纯水冰的IRM强度。冰样的IRM采集曲线与中国黄土高原原始黄土的磁铁矿和附属赤铁矿的混合贡献相兼容，其磁性能被认为与格陵兰冰中的灰尘具有相同的来源。IRM强度与冰的总沙尘质量的比较显示出非常好的相关性，但也显示出一个大的不相关磁化强度，它在不同的气候阶段基本上是恒定的，并且在测量到的沙尘浓度非常低的时间间隔是主要成分。不相关的磁化可能是由于高磁性行星际尘埃粒子（IDPs）的恒定通量或更普遍的超细颗粒气溶胶尘埃团的存在，这些尘埃团在库尔特计数器测量中基本上未被检测到。后者意味着冰期和间冰期之间的实际粉尘浓度对比比估计的要小得多。可以通过从南极冰芯获得比较数据来评估这些备选假设，南极的气溶胶尘埃通量（浓度、来源）与格陵兰岛截然不同，而国内流离失所者的通量应该大致相同。首席研究人员将测量一组样品的磁化强度，这些样品代表了来自沃斯托克冰芯的冰期和间冰期尘埃浓度的全部范围。IRM采集曲线将从12个不同的气候间隔中产生大约10个样品，使用一种新的脉冲磁化器，能够在大（~50 cc）样品上产生2.5 T的磁场，以达到饱和和高信号水平。将使用库尔特计数器在相同的样品上测量粉尘浓度。来自中等粉尘浓度的选定间隔的额外样品集将从北GRIP进行分析，以固化该地区的磁化与粉尘浓度曲线。将进行SEM-EDXRF分析以表征粉尘。对NorthGRIP和Vostok之间的磁化与尘埃浓度关系的比较将使他们能够定量估计来自地外粒子通量和可能未检测到的气溶胶尘埃质量对不相关磁化的贡献。这些新实验的结果有望对我们理解沙尘在长期气候变化中的作用具有广泛的意义。