Arctic Sea-ice Attenuation of Sea Swell, Microseism and the Prospect for using Seismology as a way to Observe Sea-ice Conditions

气候模型预测北冰洋海冰损失将加速，特别是在夏季。然而，这一预测存在不确定性，因为仅使用卫星和飞机技术很难观测到北冰洋大部分地区海冰的厚度和机械强度。解决这一难题的一种方法是通过地震学——研究北冰洋沿岸的地面振动。该项目的主要科学活动将是观察由海冰产生或以其他方式受海冰影响的特殊地面振动。其中一种信号被称为“微震”，它是由海岸线附近和远处的海洋波浪引起的地面的持续“震动”。该项目将利用阿拉斯加、加拿大和格陵兰岛北部海岸各监测站现有的几乎连续的地震数据，来探测这种微地震是如何随季节和年变化的。要取得的科学成果是创造一个连续的时间历史，记录海冰的厚度和强度在过去几十年里是如何演变的。除了研究项目的科学目标之外，更广泛的影响活动将集中在两个领域。首先，该项目将与芝加哥地区的艺术家合作，发展音乐表达的方式，以传达气候变化如何影响北极海冰状况。这种科学和艺术的互动将建立在先前的音乐作品的基础上，这些音乐作品涉及对来自南极洲冰山的地震数据的解释。其次，该项目将通过倡导和促进关于冰川地球工程作为缓解气候变化影响的一种方式的利弊的社区对话，寻求推进芝加哥大学新的气候系统工程倡议。我们建议研究微地震谱功率密度观测是否可以用来约束北冰洋北美部分（也被称为“最后冰区”，跨极漂移撞击北美大陆和格陵兰岛）的海冰特性，如浓度、厚度和“强度”（衰减由海潮产生的弯曲重力波的能力）。使用的数据来自位于阿拉斯加、加拿大北极群岛和格陵兰岛的沿海地震检波器站。海冰数据将从美国国家冰雪数据中心获得。0.1-3 s周期波段（如Tsai和McNamara， 2011）以及可能的其他频段的微震功率将与海冰强度（包括海冰浓度和海冰吸收风应力的趋势，如海冰漂移和地面风数据所示）的代理相关，并与遥感观测结果进行比较。本研究的目的是利用最简单的微地震资料经验正交函数获得最高分辨率的海冰资料经验正交函数。这包括寻找数据反演算法，通过最小化连接微地震EOFs与海冰的线性算子中的“传播”来优化“分辨率”。然后，这些算法将根据其解决海冰数据方面的能力进行分类，这些数据超出了简单的海冰浓度数据，否则这些数据是常规的，容易受到卫星数据的限制。根据这项评估的结果，地震微震观测可能为改进海冰数据提供补充信息，从而促进更好的气候模式预测。关于更广泛的影响活动，该项目将为芝加哥当地的一个艺术家联盟提供地震数据的短片段，描绘海冰产生的震颤和其他信号。这些数据将被加速，使其频率能够被听到，并将直接或间接地为音乐创作提供灵感（例如，使用乐器来模拟地震数据）。将开展更多的更广泛的影响活动，以适当地倡导有关冰川地球工程的社区对话。这种倡导将采取为美国地球物理联合会组织市政厅会议的形式，并撰写白皮书，以帮助通知美国国家科学院的极地研究委员会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Climate models predict acceleration in Arctic Ocean sea-ice loss, particularly during summer. Uncertainty in this prediction arises, however, from difficulty observing the thickness and mechanical strength of sea ice over large parts of the Arctic Ocean using just satellite and aircraft technology. One approach to addressing this difficulty is through seismology - the study of ground vibrations - along the coastline of the Arctic Ocean. The main scientific activity of this project will be to observe special ground vibrations that are generated by or otherwise influenced by sea ice. One such signal is called “microseism”, and is a constant “thrumming” of the ground caused by waves in the ocean both near and far from the coastline. The project will use existing, virtually continuous seismic data from various stations along the northern coasts of Alaska, Canada and Greenland to detect how this microseism changes with season and from year to year. The scientific outcome to be achieved is the creation of a continuous time history of how sea-ice thickness and strength have evolved over the past several decades. In addition to the scientific goals of the research project, broader impact activity will be focused in two areas. First, the project will interface with artists in the Chicago area to develop ways in which musical expressions can be developed to convey how climate change is affecting Arctic sea-ice conditions. This science and art interaction will build on previous musical compositions that involved interpretation of seismic data coming from icebergs in Antarctica. Second, the project will seek to advance the new Climate Systems Engineering initiative of the University of Chicago by advocating for and facilitating community dialogue about the pros and cons of glacial geoengineering as a way to mitigate the effects of climate change.We propose to investigate whether microseism spectral power density observations can be used to constrain sea-ice properties such as concentration, thickness, and “strength” (the ability to attenuate flexural gravity waves generated by sea swell) in the North American sector of the Arctic Ocean (also known as the “last ice area” where the transpolar drift impinges on the North American continent and Greenland). Data to be used are from coastal seismometer stations located in Alaska, the Canadian Arctic Archipelago, and Greenland. Sea-ice data will be obtained from the U.S. National Snow and Ice Data Center. The microseism power in the 0.1-3 s period band (as in Tsai and McNamara, 2011), and possibly other frequency bands, will be related to a proxy for sea-ice strength (involving sea-ice concentration and the tendency for sea ice to absorb wind stress as indicated by sea-ice drift and surface wind data) and compare with remote sensing observations. The goal of this study is to obtain the highest possible resolution of sea-ice data empirical orthogonal functions (EOFs) from the simplest possible EOFs of the microseism data. This involves seeking data-inversion algorithms that can optimize “resolving power” by minimizing “spread” in the linear operator that connects the EOFs of microseism with sea ice. The algorithms will then be categorized by their ability to resolve aspects of sea-ice data that go beyond the simple sea-ice concentration data that is otherwise routine and easy to be constrained with satellite data. Depending on the outcome of this assessment, seismic microseism observation can potentially provide complementary information to improve sea-ice data and thus facilitate better climate-model predictions. With regard to broader impact activity, the project will provide a local artist consortium in Chicago with short segments of seismic data portraying tremor and other signals generated by sea ice. These data will be sped up to allow their frequencies to be audible, and will serve to inspire musical compositions either directly or indirectly (e.g., where musical instruments are used to mimic the seismic data). Additional broader impact activity will be undertaken to appropriately advocate for community conversations about glacial geoengineering. This advocacy will take the form of organizing Town Hall meetings for the American Geophysical Union and writing white papers to help inform the Polar Research Board of the US National Academy of Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.