ICE GROUNDING EVENTS IN THE BEAUFORT SEA OFFSHORE ALASKA OBSERVED USING DISTRIBUTED ACOUSTIC SENSING

Distributed acoustic sensing (DAS) allows for the observation of natural phenomena that would be challenging using traditional sensing methods. The grounding of floating sea ice is one such phenomenon. This is due to the difficulty of deploying instruments capable of recording signals (e.g. ocean bottom seismometers and hydrophones) for an extended period in harsh offshore environments. The presence of a submarine optical fiber suitable for distributed fiber optic sensing greatly mitigates this challenge. This is the case offshore Oliktok Point, Alaska, where a telecommunication cable extends into the Beaufort Sea. We have acquired DAS data on a dark fiber at periodic intervals along a 37-km stretch of this cable since 2021. In contrast to the difficulty of acquiring the data, once analyzed the ice-grounding signals exhibit distinctive characteristics and are readily observable. We focus on a subset of these events that produce harmonic overtones and have developed a detector to identify them in the continuous data. As a preliminary step, we have analyzed 58 days of data straddling sea-ice breakup from July to October. There are over one hundred days yet to analyze, and data is still being acquired. We will present statistics on these events, including their distance offshore, duration, timing, and intensity as measured by seafloor strain-rate recorded by the DAS. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525