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

冰芯古气候记录的解释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，是理解冰盖流动的一个重要因素，因为优先排列的晶体使冰更容易在某些方向上流动。传统上，织物是通过在冰芯中间隔切割的薄片来确定的。一种新的确定构造的方法是声波测井，将探头放入井中，测量纵波穿过冰层的速度。声波测井是有价值的，因为它提供了冰结构的连续剖面，并在更大的体积上平均测量冰晶的排列。主要研究人员将测量格陵兰冰盖计划2 （GISP2）、格陵兰冰芯计划（GRIP）和北格陵兰冰芯计划（NGRIP）的声速剖面，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于识别古气候记录连续性丧失的深度，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。声波速度剖面，结合薄片数据，将用于研究如何将声波速度和薄片数据结合起来，以更好地确定冰结构。将开发一个织物估计模型，该模型使用薄截面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。声波速度剖面将用于确定是否可以通过声波测井识别古气候记录连续性丢失的深度。GISP2和GRIP通过比较两种古气候记录促进了这一确定，因为它们在此深度以上高度相关，而在此深度以下则不同。NGRIP将提供另一组重要的数据，因为选择这个位置是专门为了恢复在GISP2和GRIP发现的扰乱地层的冰。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，这些模型使用各向异性流动规律，包括织物的影响。

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.