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1. Optical polarization–based seismic and water wave sensing on transoceanic cables

   https://doi.org/10.1126/science.abe6648  

   Zhan, Zhongwen; Cantono, Mattia; Kamalov, Valey; Mecozzi, Antonio; Müller, Rafael; Yin, Shuang; Castellanos, Jorge C. (February 2021, Science)

   null (Ed.)

   Seafloor geophysical instrumentation is challenging to deploy and maintain but critical for studying submarine earthquakes and Earth’s interior. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an opportunity to fill the data gap. We successfully sensed seismic and water waves over a 10,000-kilometer-long submarine cable connecting Los Angeles, California, and Valparaiso, Chile, by monitoring the polarization of regular optical telecommunication channels. We detected multiple moderate-to-large earthquakes along the cable in the 10-millihertz to 5-hertz band. We also recorded pressure signals from ocean swells in the primary microseism band, implying the potential for tsunami sensing. Our method, because it does not require specialized equipment, laser sources, or dedicated fibers, is highly scalable for converting global submarine cables into continuous real-time earthquake and tsunami observatories. 

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2. Multi‐Scale Thermal Mapping of Submarine Groundwater Discharge in Coastal Ecosystems of a Volcanic Area

   https://doi.org/10.1029/2024GL111857  

   Williams, Ebony_L; Kratt, Christopher_B; Rodolfo, Raymond_S; Lapus, Mark_R; Lardizabal, Ryan_R; Bangun, Aya_S; Nguyen, Amber_T; Tyler, Scott_W; Cardenas, M_Bayani (November 2024, Geophysical Research Letters)

   Abstract Submarine groundwater discharge (SGD) in volcanic areas commonly exhibits high temperatures, concentrations of metals and CO₂, and acidity, all of which could affect sensitive coastal ecosystems. Identifying and quantifying volcanic SGD is crucial yet challenging because the SGD might be both discrete, through fractured volcanic rock, and diffuse. At a volcanic area in the Philippines, the novel combination of satellite and drone‐based thermal infrared remote sensing, ground‐based fiber‐optic distributed temperature sensing, and in situ thermal profiling in coastal sediment identified the multi‐scale nature of SGD and quantified fluxes. We identified SGD across ∼30 km of coastline. The different approaches revealed numerous SGD signals from the intertidal zone to about a hundred meters offshore. In active seepage areas, temperatures peaked at 80°C, and Darcy fluxes were as high as 150 cm/d. SGD is therefore locally prominent and regionally important across the study area. 

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3. Multiplexed Distributed Acoustic Sensing Offshore Central Oregon

   https://doi.org/10.1785/0220240460  

   Shi, Qibin; Williams, Ethan F; Lipovsky, Bradley P; Denolle, Marine A; Wilcock, William_S D; Kelley, Deborah S; Schoedl, Katelyn (February 2025, Seismological Research Letters)

   Abstract Distributed acoustic sensing (DAS) on submarine fiber-optic cables is providing new observational insights into solid Earth processes and ocean dynamics. However, the availability of offshore dark fibers for long-term deployment remains limited. Simultaneous telecommunication and DAS operating at different wavelengths in the same fiber, termed optical multiplexing, offers one solution. In May 2024, we collected a four-day DAS dataset utilizing an L-band DAS interrogator and multiplexing on the submarine cables of the Ocean Observatory Initiative’s Regional Cabled Array offshore central Oregon. Our findings show that multiplexed DAS has no impact on communications and is unaffected by network traffic. Moreover, the quality of DAS data collected via multiplexing matches that of data obtained from dark fiber. With a machine-learning event detection workflow, we detect 31 T waves and the S wave of one regional earthquake, demonstrating the feasibility of continuous earthquake monitoring using the multiplexed offshore DAS. We also examine ocean waves and ocean-generated seismic noise. We note high-frequency seismic noise modulated by low-frequency ocean swell and hypothesize about its origins. The complete dataset is freely available. 

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4. Impacts of Hydrostatic Pressure on Distributed Temperature-Sensing Optical Fibers for Extreme Ocean and Ice Environments

   https://doi.org/10.3390/photonics11070630  

   Tyler, Scott W; Silvia, Matthew E; Jakuba, Michael V; Durante, Brian M; Winebrenner, Dale P (July 2024, Photonics)

   Optical fiber is increasingly used for both communication and distributed sensing of temperature and strain in environmental studies. In this work, we demonstrate the viability of unreinforced fiber tethers (bare fiber) for Raman-based distributed temperature sensing in deep ocean and deep ice environments. High-pressure testing of single-mode and multimode optical fiber showed little to no changes in light attenuation over pressures from atmospheric to 600 bars. Most importantly, the differential attenuation between Stokes and anti-Stokes frequencies, critical for the evaluation of distributed temperature sensing, was shown to be insignificantly affected by fluid pressures over the range of pressures tested for single-mode fiber, and only very slightly affected in multimode fiber. For multimode fiber deployments to ocean depths as great as 6000 m, the effect of pressure-dependent differential attenuation was shown to impact the estimated temperatures by only 0.15 °K. These new results indicate that bare fiber tethers, in addition to use for communication, can be used for distributed temperature or strain in fibers subjected to large depth (pressure) in varying environments such as deep oceans, glaciers and potentially the icy moons of Saturn and Jupiter. 

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5. Distributed acoustic sensing recordings of low-frequency whale calls and ship noise offshore Central Oregon

   https://doi.org/10.1121/10.0017104  

   Wilcock, William_S_D; Abadi, Shima; Lipovsky, Bradley_P (February 2023, JASA Express Letters)

   Distributed acoustic sensing (DAS) is a technique that measures strain changes along an optical fiber to distances of ∼100 km with a spatial sensitivity of tens of meters. In November 2021, 4 days of DAS data were collected on two cables of the Ocean Observatories Initiative Regional Cabled Array extending offshore central Oregon. Numerous 20 Hz fin whale calls, northeast Pacific blue whale A and B calls, and ship noises were recorded, highlighting the potential of DAS for monitoring the ocean. The data are publicly available to support studies to understand the sensitivity of submarine DAS for low-frequency acoustic monitoring. 

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