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

科学能提供的最有趣的历史记录之一包含在南极洲的冰层中。几十万年来，积雪在冰盖上层层沉淀，变得紧密，变成了额外的冰。空气或雪中的任何灰尘或其他杂质也被沉淀，因此每一次降雪都留下了在沉积时或接近沉积时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可以获得火山喷发的详细年表。通常，对火山层的分析需要从冰盖中物理提取岩芯；然而，从岩心获得年表具有不连续性，而且很难、耗时和昂贵地获得。钻孔测井是一种测量方法，在这种方法中，无论岩心是否已被取回，都要将仪器放入冰层中的钻孔中。到目前为止，这项技术只被用于测量光学系统，以识别火山灰和其他杂质层。在这个项目中，将开发一种测量冰传导性的剖面图技术。降低到井眼中的射频发射器将产生一个返回信号，该信号会根据当地的电导率而变化，而当地的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将能够帮助快速识别对全球有潜在影响的火山喷发，通过它们的频率依赖性区分不同的溶解离子，并帮助建立不同冰芯和钻孔之间的年表。第二部分：技术说明极地冰盖的钻孔记录是地球科学家识别火山喷发和确定火山喷发日期的最重要方法之一。然而，目前的技术只显示了火山喷发产生的火山灰的存在和深度。为了提取更详细的信息，必须获取冰芯，并使用电导率或介电测量来费力地测量实验室中的每个部分，以确定是否存在溶解的硫酸盐及其相对于相应火山灰的位置(如果有的话)。该计划将研究和演示一种与钻孔测井兼容的射频介电传感器，以检测和测量冰中溶解的主要离子化学成分的尖峰，特别是在与火山产生的硫酸盐相对应的间隔内。硫酸盐层是火山产品的主要标志之一。然而，其他离子，如氯化物、钙和其他离子也常见于冰中，该项目的介电测井技术也将测量这些离子。预计某些离子组将可以通过它们的频率相关性来区分。这项技术可以引导其他使用常规岩心扫描和取样方法的调查人员找到对相应岩心特别感兴趣的区域。我们计划构建一个基于环的电极系统，并在各种人造冰孔和冰芯上测试该系统。该装置将不包括压力容器或其他井眼记录仪填料。我们将测试施加电信号的不同方法，包括短脉冲和周期波。我们将进一步利用具有低噪声电路和过滤器的差动测量来实现最高灵敏度。我们将提取的信号与已知的硫酸盐和其他离子的摩尔数以及测量的ECM记录相关联。我们将使用储存在加州大学伯克利分校S实验室的真实冰芯进行缩小实验。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。这个小收藏品包括来自南极洲和格陵兰岛不同地点的岩芯，以及各种历史长达100万年的岩芯。

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.