Hydraulic Conductivity Measurements, Utqiagvik (Barrow), Alaska, 2014

Six individual ice cores were collected from the Barrow Environmental Observatory in Barrow, Alaska, in May of 2013 as part of the Next Generation Ecosystem Experiment (NGEE). Each core was drilled at a different location to varying depths. After drilling, the cores were stored in coolers packed with dry ice and flown to Lawrence Berkeley National Laboratory (LBNL) in Berkeley, CA. 3-dimensional images of the cores were constructed using medical X-ray computed tomography (CT) scanner at 120kV. Hydraulic conductivity samples were extracted from these cores at LBNL Richmond Field Station in Richmond, CA, in February 2014 by cutting 5 to 8 inch segments using a chop saw. Samples were packed individually and stored at -20C freezing temperatures to minimize any changes in structure or loss of ice content prior to analysis. Hydraulic conductivity was determined through falling head tests using a permeameter [ELE International, Model #: K-770B] (Appendix A). Samples were placed in a latex membrane via a membrane stretcher while frozen. Use of a membrane stretcher made the membranes easier to secure and minimized contact with the sample. A clear polycarbonate sleeve, fabricated with a stainless steel ring at the bottom to keep the sleeve from floating, was placed around the sample inside the permeameter to minimize deformation during analysis. The permeameter was filled with water and 1.0 PSI of air was applied for confining pressure during sample defrost. Outflow valves were left open to allow for incremental thawing and samples were left to thaw for approximately 12 hours. After approximately 12 hours of thaw, initial falling head tests were performed. When the flow was significantly too fast or too slow, the analysis was stopped and the burette size was adjusted accordingly (i.e. a larger diameter burette was used for flows that were faster than desired or a smaller diameter burette was used for flows that were slower than desired). Two to four measurements were collected on each sample and collection stopped when the applied head load exceeded 25% change from the original load. Analyses were performed between 2 to 3 times for each sample. The final hydraulic conductivity calculations were computed using methodology of Das et al., 1985.The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a 15-year research effort (2012-2027) to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).

2013年5月，作为下一代生态系统实验（Next Generation Ecosystem Experiment, NGEE）的一部分，研究人员从阿拉斯加州巴罗的巴罗环境观测站采集了6根独立冰芯。每根冰芯均在不同位置钻取，且钻取深度各不相同。钻取完成后，冰芯被存放于装有干冰的冷藏箱中，并空运至加利福尼亚州伯克利的劳伦斯伯克利国家实验室（Lawrence Berkeley National Laboratory, LBNL）。研究人员使用120kV医用X射线计算机断层扫描（computed tomography, CT）扫描仪构建了冰芯的三维图像。
研究人员于2014年2月在加利福尼亚州里士满的LBNL里士满野外站对这些冰芯开展导水率样本提取工作：使用斜切锯切割出5至8英寸的冰芯段。每个样本单独封装，并在-20℃的冷冻环境下储存，以尽可能避免样本结构发生变化或冰含量流失，直至后续分析。
导水率通过水头下降试验，使用渗透仪[ELE国际公司，型号：K-770B]（详见附录A）测定。测试时，样本在冷冻状态下通过膜拉伸器装入乳胶膜中——使用膜拉伸器可更便捷地固定膜材，并减少与样本的接触。在渗透仪内的样本外围套有一个透明聚碳酸酯套筒，套筒底部配有不锈钢环以防止漂浮，从而尽可能降低分析过程中样本发生形变的可能。
渗透仪注满水后，施加1.0 PSI的空气作为围压，同时开启出水阀以实现逐步解冻，样本静置解冻约12小时。解冻约12小时后，开展初始水头下降试验。若流速明显过快或过慢，则终止当前分析并调整滴定管规格：对于流速高于预期的样本更换大直径滴定管，流速低于预期的则更换小直径滴定管。每个样本采集2至4组测量数据，当施加的水头荷载与初始荷载偏差超过25%时，停止数据采集。每个样本的分析重复2至3次，最终导水率计算采用Das等人1985年提出的方法。
下一代北极生态系统实验（Next-Generation Ecosystem Experiments: Arctic, NGEE Arctic）是一项为期15年（2012-2027年）的研究项目，旨在通过建立对富碳北极生态系统的预测性认知以及其对气候的反馈机制，降低地球系统模型的不确定性。该项目由美国能源部生物与环境研究办公室资助。NGEE Arctic设有两个野外研究站点：其一位于阿拉斯加州乌特恰维克（原巴罗）附近北坡的巴罗环境观测站（Barrow Environmental Observatory, BEO）内的北极多边形苔原沿海区域；其二位于阿拉斯加州诺姆以北的苏厄德半岛不连续多年冻土区的多处区域。
通过实地观测、受控实验以及与现有数据集的综合分析，NGEE Arctic为多尺度建模提供了更完善的知识库，并助力美国能源部地球系统模型——能源极端尺度地球系统模型（Energy Exascale Earth System Model, E3SM），尤其是其陆面模型组件（E3SM陆面模型，ELM），在全球泛北极尺度下改进过程表征。