Collaborative Research: Borehole Logging to Classify Volcanic Signatures in Antarctic Ice

科学所能提供的最有趣的历史记录中，只有南极洲的冰记录了。在数十万年的时间里，雪一层一层地沉淀在冰盖上，变得密实，变成额外的冰。空气或雪中的任何灰尘或其他杂质也被沉淀下来，因此每次降雪都会留下在沉积时或附近存在的大气的快照记录。从火山灰和其他火山产物沉积的冰层中可以得到火山喷发的详细年表。通常情况下，对火山层的分析需要从冰盖中物理提取一个核心；然而，岩心的年表具有不连续性，而且难以获得，耗时且昂贵。井眼测井是一种测量方法，无论岩心是否被取走，都要将仪器放入冰面上的钻孔中。迄今为止，这项技术仅用于测量光学系统，以识别火山灰和其他杂质层。在这个项目中，将开发一种剖面技术来测量冰的导电性。将射频发射器放入井眼中，将产生一个根据局部电导率变化的返回信号，而电导率又取决于溶解离子的浓度。例如，溶解的硫酸盐是火山活动的关键标志，可能与沉积的火山灰不一致。其他溶解的离子，如氯化物，可以指示其他过程。预计这种钻孔剖面仪器将能够帮助快速识别具有潜在全球影响的火山爆发，通过频率依赖性区分不同的溶解离子，并协助建立不同冰芯和钻孔之间的年表。第二部分：技术描述极地冰盖的钻孔测井是地球科学家识别和确定火山喷发日期的最重要方法之一。然而，目前的技术只能显示火山喷发产生的火山灰的存在和深度。为了获得更详细的信息，人们必须获得一个冰芯，并在实验室中用电导率或介电测量艰苦地测量每个部分，以确定溶解的硫酸盐的存在或不存在，以及它相对于相应灰烬的位置（如果有的话）。该项目将研究和演示一种与井眼测井兼容的射频介电传感器，用于探测和测量冰中溶解主要离子化学的峰值，特别是在与火山产生的硫酸盐相对应的间隔中。硫酸盐层是火山产物的主要特征之一。然而，其他离子，如氯化物、钙等也常见于冰中，本项目的介电测井技术也将测量这些离子。预期某些离子组可以通过它们的频率依赖性来区分。这项技术可以指导其他使用传统岩心扫描和采样方法的研究人员在相应的岩心中找到特别感兴趣的区域。我们计划构建一个基于环的电极系统，并在各种人工冰钻孔和冰芯上进行测试。该装置不包括压力容器或其他井眼记录器填料。我们将测试不同的应用电信号的方法，包括短脉冲和周期波。我们将进一步利用低噪声电路和滤波器的差分测量来实现最大的灵敏度。我们将把提取的信号与已知的硫酸盐和其他离子的摩尔浓度和测量的ECM记录联系起来。我们将使用储存在海湾的真正冰芯进行按比例缩小的实验。他在加州大学伯克利分校的实验室说。这将允许在具有天然杂质和多晶结构的冰中测试不同的设计。这个小收藏包括来自南极洲和格陵兰岛不同地点的岩心，年龄各不相同，年龄可达100万年。

Part I: NontechnicalOne of the most interesting historical records that science can provide is contained in the ice of Antarctica. Layer by layer over hundreds of thousands of years, snow has precipitated on the ice sheet, become compacted, and turned into additional ice. Any dust or other impurities in the air or snow have been precipitated as well and thus each snowfall leaves a snapshot record of the atmosphere that existed at or near the time of deposition. A detailed chronology of volcanic eruptions can be obtained from the ice layers where ash and other volcanic products were deposited. Normally, the analysis of volcanic layers requires the physical extraction of a core from the ice sheet; however, chronologies from cores have discontinuities and are difficult, time-consuming, and expensive to obtain. Borehole logging is a measurement method where one lowers instrumentation into a drilled hole in the ice, whether or not core has been retrieved. To date, this technology has only been used to measure optical systems to identify volcanic ash and other impurity layers. In this program, a profiling technology will be developed that measures the conductivity of the ice. A radio-frequency emitter lowered into the borehole will create a return signal that changes depending on the local conductivity, which depends on the concentration of dissolved ions. For example, dissolved sulfates are a critical marker of volcanic activity that may not be coincident with deposited ash. Other dissolved ions, such as chloride, can be indicative of other processes. It is expected that this borehole profiling instrument will be able to help rapidly identify volcanic eruptions that had potentially global impact, distinguish between different dissolved ions via their frequency dependencies, and assist in establishing chronologies between different ice cores and boreholes.Part II: Technical DescriptionBorehole logging of the Polar ice sheets is one of the most important methods that earth scientists have to identify and date volcanic eruptions. However, current technology only indicates the presence and depth of ash from an eruption. In order to extract more detailed information, one must obtain an ice core, and laboriously measure each section in the laboratory using electrical conductivity or dielectric measurements to determine the presence or absence of dissolved sulfate and its location relative to the corresponding ash, if any. This program will investigate and demonstrate a borehole logging-compatible radio-frequency dielectric sensor to detect and measure spikes in dissolved major ions chemistry in ice, particularly in intervals corresponding to volcanically produced sulfates. The sulfate layers are one of the primary signatures of volcanic products. However, other ions, such as chlorides, calcium, and others are also commonly seen in ice, and the dielectric logging technology of this program would also measure these. It is expected that certain sets of ions will be distinguishable by their frequency dependencies. This technique could guide other investigators, who are using conventional core scanning and sampling methods, to regions of special interest in corresponding core.We plan to construct a ring-based electrode system and test this system on a variety of artificial ice boreholes and ice cores. This unit will not include a pressure vessel or other borehole logger packing. We will test different means of applying electrical signals including short pulses and periodic waves. We will further utilize differential measurements with low noise circuits and filters to achieve maximum sensitivity. We will correlate the signals extracted with known molarities of sulfates and other ions and measured ECM records. We will perform scaled-down experiments using real ice cores stored in Bay?s lab at UC Berkeley. This will permit testing of different designs in ice with natural impurities and polycrystalline structure. This small collection includes cores from a variety of locations in Antarctica and Greenland, and a variety of ages as old as a million years.