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

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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.