Interpretation of Arctic North Slope Permafrost Borehole Thermal Evolution in Light of Spatial and Temporal Variation in Surface Temperature Fields

永久冻土是指温度低于0°C超过两年的土地。它是北半球冰雪圈中面积最大的区域。永久冻土、水文循环和大气之间的反馈是北极系统的关键组成部分。由于多年冻土的健康直接取决于温度，因此多年冻土的热状态是气候变化的关键信号之一。此外，冻土的厚度、分布和温度对北极的生态和工程都有影响。在大气层和永久冻土层的顶部之间是活土层，它每年冻结和融化一次。这个活动层在地球上转换气候信号？热流流入或流出下面的导电永久冻土。根据众所周知的传导物理学，可以从有源层内部的温度曲线确定有源层底部的热流密度。这个项目的目标是确定阿拉斯加永久冻土的时空变化模式。北极北坡，以及控制这些模式的关键过程。20世纪70年代从废弃的勘探钻孔中记录的温度曲线表明，永久冻土层已经明显变暖到几十米深，这种模式可以用过去半个世纪里2-4°C的表面变暖来最好地解释。从那时起，横跨阿拉斯加国家石油储备（NPR-A）的21个钻孔被美国地质勘探局的研究人员反复重新记录，提供了一个戏剧性变化的记录。对这些剖面最简单的解释表明，地表温度的增加速度更快，在20世纪90年代发生了每十年3°C的变化。地面气象学和活动层热结构已同时记录在跨越该地区的一系列自动化地面站中，并已维持了10至20年的周期。其中9个地面站与深钻孔位于同一位置；所有这些都融入了监测全球热状态的国际努力？永久冻土。美国地质勘探局的网络代表了世界上最大的用于监测永久冻土热状态的深钻孔阵列，以及全球网络中最密集的地面站阵列。研究人员将整合从深钻孔中定期收集的温度剖面观测数据，以及1-2小时的近地表气象和近地表土壤温度观测数据，以约束进入永久冻土的能量的时空记录。它还将从测量间隔（1970年代以后）的钻孔测量中提取最干净的气候信号，目的是回答有关景观热状态及其演变过程的问题。为了实现这些目标，PI将首先与美国地质勘探局的同事合作，最终确定其观测结果的质量控制（初步数据可在：http://data.usgs.gov/climateMonitoring/region/ show?region=alaska）。然后，他将开发数值模型，根据特定地点的影响（例如，钻探时间的长短，湖泊的存在）来预测热扰动。最后，使用最干净的？气候变暖的信号和热量流入永冻层，研究小组将分析这一信号的时空格局。结果将通过科学文献和社区表面动力学建模系统（CSDMS, http://csdms.colorado.edu/wiki/Main_Page）教育资源库获得。我们将开发基于此数据集、建模工作和最终分析的交互式模型、动画和课堂练习。

Permafrost is ground that has remained below 0°C for more than two years. It has the greatest areal extent of any component of the cryosphere in the Northern Hemisphere. Feedbacks between permafrost, the hydrologic cycle, and the atmosphere are key components of the Arctic system. As the health of permafrost is directly dependent upon temperature, the thermal state of permafrost is one of the key signals of climate change. In addition, the thickness, distribution and temperature of permafrost influences both ecology and engineering in the Arctic. Between the atmosphere and the top of the permafrost is the active layer, which freezes and thaws on an annual basis. This active layer translates the climate signal at the Earth?s surface into heat flow into or out of the underlying conductive permafrost. The heat flux at the base of the active layer can be determined from profiles of temperature within the active layer, based on well-known physics of conduction. The goal in this project is to identify both spatial and temporal patterns of change in the permafrost of Alaska?s Arctic North Slope, and the critical processes that govern these patterns. Temperature profiles documented in the 1970s from abandoned exploratory boreholes suggested that the permafrost had warmed significantly to depths of many tens of meters, in a pattern that could be best explained by a 2-4°C surface warming over the prior half century. Since then, an array of 21 boreholes, spanning the National Petroleum Reserve-Alaska (NPR-A), has been repeatedly re-logged by USGS researchers, providing a record of dramatic change. The simplest interpretation of these profiles suggests yet more rapid increases in surface temperature, with a change of 3°C/decade occurring in the 1990s. The surface meteorology and active layer thermal structure has simultaneously been documented in an array of automated surface stations that span the region, and have been maintained for periods ranging from one to two decades. Nine of these surface stations are co-located with deep boreholes; all are embedded in international efforts to monitor the thermal state of the globe?s permafrost. The USGS network represents both the largest array of deep boreholes in the world used for monitoring the thermal state of the permafrost, and the densest array of surface stations in the global network.The investigators will integrate the observations of temperature profiles collected periodically from the deep boreholes, and 1-2 hourly observations of near surface meteorology and near surface soil temperature, to constrain the spatial and temporal record of the energy going into the permafrost. It will also extract the cleanest climate signal possible from the borehole measurements over the measurement interval (1970s onward) with the aim of answering questions about the thermal state of the landscape and the processes responsible for its evolution. To accomplish these goals the PI will first work with USGS colleagues to finalize quality control of their observations (preliminary data available at: http://data.usgs.gov/climateMonitoring/region/ show?region=alaska). He will then develop numerical models that predict the thermal disturbance from site-specific effects (e.g., length of time drilling, presence of lakes). Finally, using the ?cleanest? climate signal of warming and heat flow into the permafrost, the team will analyze the spatial and temporal pattern of this signal.Results will be available through both the scientific literature, and the Community Surface Dynamics Modeling System (CSDMS, http://csdms.colorado.edu/wiki/Main_Page) Educational repository. We will develop interactive models, animations, and classroom exercises based on this dataset, modeling effort, and final analysis.