Passive Underwater Acoustic Monitoring of LeConte Glacier and the Effects of an Ice Mélange at the Ocean Surface

Matthew C Zeh1, Erin C Pettit2, Megan S Ballard3, Preston Wilson1, Jonathan D Nash4, Nicole Bohall2, Jason M Amundson5, Christian Kienholz5, Roman J Motyka5, David Sutherland6, Alexander Hager6 and Rebecca H Jackson7, (1)University of Texas at Austin, Walker Department of Mechanical Engineering and Applied Research Laboratories, Austin, TX, United States, (2)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, OR, United States, (3)Applied Research Laboratories at the University of Texas at Austin, Austin, United States, (4)Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, United States, (5)University of Alaska Southeast, Juneau, AK, United States, (6)University of Oregon, Department of Earth Sciences, Eugene, United States, (7)Rutgers University, New Brunswick, NJ, United States
Abstract:
The rapidly changing cryosphere has led to increased interest within military and ecological communities to better understand the poorly characterized physical processes governing ice-ocean boundaries. These processes are no more pronounced than within glacial fjords where massive glaciers flow towards and meet the ocean. These environments are dynamic, sensitive to fresh- and sea-water balances and are significantly louder than other ice-covered environments [Pettit, Geophys. Res. Letters 42, 2309-2316 (2015)]. The ambient noise provided by the active glacier, including calving, ice cracking, and bubbles escaping from within the glacier ice, provides insight into the processes taking place at the boundary. The abundant acoustic information, as well as the inherent difficulty in experimentally measuring the physical processes occurring below the water surface, present passive acoustic monitoring as a promising tool to observe short- and long-term changes in this system. Acoustic measurements were obtained with a 6-element hydrophone array deployed in LeConte Bay, a glacierized fjord in southeastern Alaska, from October 2016 to September 2017. This work examines the abrupt change in the character, variability, and sound pressure level within these acoustic recordings during the period of late-February to mid-April 2017 when a densely packed, slow moving ice mélange was present on the water surface in the fjord. Through integrating this acoustic data with time-lapse imagery and oceanographic moorings, this work addresses the role the mélange plays as both acoustic source and propagation boundary in this unique noise environment.