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Seismic instruments such as broadband seismometers and distributed acoustic sensors (DAS) have a demonstrated potential for wide‐scale and continuous in situ monitoring of near‐surface environmental and anthropogenic processes. DAS is attractive for development as a multi‐geophysical observatory due to the prevalence of existing fiber infrastructure in regions with environmental, cultural, or strategic significance. Here we present results from a multi‐seasonal acquisition of DAS data on a seafloor cable in the Beaufort Sea, Alaska. During a November 2021 data collect we captured the rapid transition of ambient noise characteristics from an "ice‐free" state to an "ice‐bound" state. A sea ice formation front was plainly visible on the DAS record and was observed to propagate 20 km seaward over a period of 8 hr. Satellite‐based instrumentation were unable to record this event due to cloud cover, low light conditions, and orbital frequency. Plain Language Summary: Distributed acoustic sensing (DAS) is an emerging technology that uses fiber optic cable to mimic a high resolution array of one dimensional seismometers. Distributed acoustic sensors is compatible with any single‐mode fiber optic cable, including seafloor telecommunications cables. Previous recordings of DAS data on seafloor cables have demonstrated that this technology is able to detect and track individual ocean waves, surface vessels, and whales. In this first‐ever acquisition of DAS data from a seafloor beneath a frozen ocean, we show that DAS is also capable of mapping sea ice coverage with unprecedented spatial resolution and can track sea ice formation and breakup up in near real time. Key Points: Seafloor distributed acoustic sensing can distinguish between sea ice and open water on the basis of endemic wave modesThis technology is capable of high resolution, near real time imaging of sea ice dynamics, such as rapid freezing of marginal iceThis can complement large scale, low resolution satellite‐based imaging in regions of high scientific or operational importance [ABSTRACT FROM AUTHOR]

Single‐frequency microseisms (SFMs) have been revealed to be only generated in shallow water for decades, while some recent studies reported them in a deep ocean. Using the continuous waveform data recorded by ocean bottom seismometers, we investigate the deep ocean SFMs in the northern Philippine Sea. Based on the spectrum analysis, we find that the SFMs can be detected in deep ocean and the detection is time variable. To determine the source locations of SFMs, we perform polarization analysis and calculate the cross‐correlation coefficients between SFMs on vertical components and ocean wave energy spectra considering the attenuation of SFMs. Both the polarization and correlation results show that the sources nearby stations dominate the observed Rayleigh‐wave SFMs though distant sources also contribute. Our investigation suggests that the SFMs can be generated in a deep ocean likely by infragravity ocean waves interacting with seafloor topography, which is strengthened by strong ocean storms. Plain Language Summary: Microseisms are seismic noise caused by ocean waves impacting on the seafloor and recorded by seismic stations. Those of microseisms have similar periods of 10–20 s as ocean waves are called single‐frequency microseisms (SFMs), which are generally considered to be excited only in shallow water. Here we show that SFMs can be detected in a deep ocean from time to time especially when strong ocean storms impact. Combining the source azimuthal distributions of SFMs as well as the correlations between SFMs and ocean wave energy, we demonstrate that the derived dominating sources of abyssal SFMs are local, mostly nearby stations. The generating mechanism of the local SFMs is likely that long‐period ocean waves strengthened by strong ocean storms impact with the rugged seafloor topography. Key Points: The signals of single‐frequency microseisms can be detected in deep ocean greater than 2,000 m with temporal featuresThe Rayleigh‐wave single‐frequency microseisms (SFMs) observed are revealed to be mainly excited by the localized sourcesInfragravity ocean waves strengthened by storms and seafloor topography play important roles in the generation of deep ocean SFMs [ABSTRACT FROM AUTHOR]

Gravity waves impacting ice shelves illicit a suite of responses that can affect ice shelf integrity. Broadband seismometers deployed on the Ross Ice Shelf, complemented by a near‐icefront seafloor hydrophone, establish the association of strong icequake activity with ocean gravity wave amplitudes (AG) below 0.04 Hz. The Ross Ice Shelf‐front seismic vertical displacement amplitudes (ASV) are well correlated with AG, allowing estimating the frequency‐dependent transfer function from gravity wave amplitude to icefront vertical displacement amplitude (TGSV(f)). TGSV(f) is 0.6–0.7 at 0.001–0.01 Hz but decreases rapidly at higher frequencies. Seismicity of strong icequakes exhibits spatial and seasonal associations with different gravity wave frequency bands, with the strongest icequakes observed at the icefront primarily during the austral summer when sea ice is minimal and swell impacts are strongest. Key Points: Rift and icefront icequakes were identifiedIcefront icequakes are most frequent during the austral summer when swell forcing is greatest in the absence of sea iceAn empirical ocean‐to‐ice shelf displacement transfer function is obtained [ABSTRACT FROM AUTHOR]

Understanding deformation in ice shelves is necessary to evaluate the response of ice shelves to thinning. We study microseismicity associated with ice shelf deformation using nine broadband seismographs deployed near a rift on the Ross Ice Shelf. From December 2014 to November 2016, we detect 5,948 icequakes generated by rift deformation. Locations were determined for 2,515 events using a least squares grid‐search and double‐difference algorithms. Ocean swell, infragravity waves, and a significant tsunami arrival do not affect seismicity. Instead, seismicity correlates with tidal phase on diurnal time scales and inversely correlates with air temperature on multiday and seasonal time scales. Spatial variability in tidal elevation tilts the ice shelf, and seismicity is concentrated while the shelf slopes downward toward the ice front. During especially cold periods, thermal stress and embrittlement enhance fracture along the rift. We propose that thermal stress and tidally driven gravitational stress produce rift seismicity with peak activity in the winter. Plain Language Summary: In Antarctica, large bodies of floating ice called ice shelves help prevent ice on land from sliding into the ocean. To predict how Antarctica might respond to climate change, we need to understand how ice shelves interact with the environment, including the atmosphere and the ocean. The largest ice shelf, the Ross Ice Shelf, is over 500,000 km2 in area, making it the largest body of floating ice in the world. In this study, we deployed nine seismographs, the same instruments used to study earthquakes, to monitor vibrations and cracking within the Ross Ice Shelf over a 2‐year period. During that time, the instruments detected nearly 6,000 fracture events along a 120‐km‐long crack in the ice shelf. We compared the timing of the cracking to air temperature data, ocean wave activity, and tides to see whether these factors influenced the crack's behavior. We found that fracture occurs most frequently just after high tide during winter and when the air is very cold. We also found that fracture at the rift is not triggered by ocean waves. This work demonstrates that Antarctic ice shelves are very sensitive to the environment and highlights the need to continue studying them. Key Points: 2,515 icequakes associated with rift deformation on the Ross Ice Shelf are located using a double‐difference location algorithmIcequake timing correlates with tidal phase diurnally and inversely correlates with air temperature on multiday and seasonal time scalesOcean swell, infragravity waves, and a significant tsunami arrival are not correlated with increased rift activity [ABSTRACT FROM AUTHOR]