Collaborative Research: Sonic Logging of GISP2, GRIP and NGRIP Boreholes

冰芯古气候记录的OPP-00-82469LamoreyOPP-00-82469WaddingtonInterpretation依赖于对冰盖流动的理解，以确定深度-年龄关系以及冰是否受到褶皱的影响。冰中晶体的排列被称为结构，这是理解冰盖流动的一个重要因素，因为优先排列的晶体会使冰更容易向特定方向流动。传统上，织物是通过在冰芯中每隔一段时间切割薄片来确定的。一种新的确定结构的方法是声波测井，将探头放入钻孔中测量穿过冰层的纵波速度。声波测井很有价值，因为它提供了冰结构的连续剖面，并在比薄片更大的体积上平均冰晶的排列。首席调查人员将在格陵兰冰盖计划2(GISP2)、格陵兰冰芯计划(GRIP)和北部格陵兰冰芯计划(NGRIP)测量声速剖面，并利用它们：1)提高对薄片和声速数据之间关系的理解；2)确定声速数据是否可以用来识别失去古气候记录连续性的深度，如果可以，则制定识别该深度的标准；3)为各向异性流动规律模型提供验证和输入数据。声速剖面结合薄层数据将被用来研究如何将声速和薄层数据结合起来以更好地确定冰组构。将开发一种织物评估模型，该模型使用薄片数据和速度剖面来预测织物参数及其不确定性和空间变异性。声波速度剖面将被用来确定是否可以从声波测井中识别失去古气候记录连续性的深度。GISP2和GRIP通过比较两个古气候记录促进了这一确定，因为它们在这个深度以上高度相关，在这个深度以下背离。NGRIP将提供另一组重要的数据，因为这个地点是专门为了恢复在GISP2和GRIP发现的扰乱地层的冰而选择的。最后，GISP2、GRIP和NGRIP声波测井将用于验证和约束最新一代的冰盖流动模型，该模型使用各向异性流动定律来考虑织物的影响。

Abstract OPP-00-82469LamoreyOPP-00-82469WaddingtonInterpretation of paleoclimate records from ice cores depends on understanding the ice sheet flow to determine depth-age relationships and whether the ice has been affected by folding. The alignment of crystals in ice, called fabric, is an important factor in understanding ice sheet flow because preferentially aligned crystals cause the ice to flow more easily in certain directions. Fabrics have traditionally been determined by using thin sections cut at intervals in the ice core. A new method of determining fabric is sonic logging, where a probe is lowered into a borehole to measure the velocity of compressional waves through the ice. Sonic logging is valuable because it provides a continuous profile of the ice fabric and averages the alignment of ice crystals over a larger volume than do thin sections. The Principal Investigators will measure sonic velocity profiles at the Greenland Ice Sheet Project 2 (GISP2), Greenland Ice Core Program (GRIP), and Northern Greenland Ice Core Program (NGRIP) and use them to: 1) improve the understanding of the relationship between thin section and sonic velocity data; 2) determine if sonic velocity data can be used to identify the depth at which paleoclimate record continuity is lost and if so, formulate criteria to identify this depth; and 3) provide verification and input data for anisotropic flow law models.Sonic velocity profiles, combined with thin section data, will be used to investigate how sonic velocities and thin section data can be combined to better determine ice fabric. A fabric estimation model will be developed that uses thin section data and velocity profiles to predict fabric parameters and their uncertainty and spatial variability. The sonic velocity profiles will be used to determine if the depth at which the paleoclimate record continuity is lost can be identified from sonic logging. This determination was facilitated at GISP2 and GRIP by comparing two paleoclimate records because they correlate highly above this depth and diverge below it. NGRIP will provide another important set of data because this location was chosen specifically to recover ice that was found to have disturbed stratigraphy at GISP2 and GRIP. Finally, the GISP2, GRIP, and NGRIP sonic logs will be used to verify and constrain the latest generation of ice sheet flow models that use an anisotropic flow law to include the effect of fabric.