An acoustic sound source manufactured at the Marine Science Development Center for Scripps researcher Matthew Dzieciuch being deployed in the Arctic Ocean from the U.S. Coast Guard Icebreaker Healy. Acoustic systems like these are uniquely able to monitor under the ice where satellites are compromised, and provide an unprecedented look at the changing Arctic environment.
Photo Credit: Lee Freitag/WHOI
Scientific Frontline: Extended "At a Glance" Summary: Ocean Acoustic Thermometry in the Arctic
The Core Concept: Ocean acoustic thermometry is a remote sensing technique that utilizes the travel time of underwater acoustic signals to precisely measure and continuously monitor ocean temperatures beneath sea ice.
Key Distinction/Mechanism: The mechanism relies on the physical principle that sound travels faster in warmer water and slower in colder water. By transmitting acoustic signals between bottom-anchored moorings across vast distances and measuring the exact time of arrival, researchers can accurately infer the average temperature of the water the sound passed through. This approach effectively bypasses the limitations of satellite sensors, which are blocked by surface ice, and ship-based measurements, which are restricted by challenging access.
Major Frameworks/Components:
- Acoustic Propagation: The primary physical principle linking the speed of sound in seawater directly to its thermal properties.
- Bottom-Anchored Moorings: Specialized underwater acoustic transmitter and receiver networks anchored to the seafloor, designed to operate continuously under harsh, ice-covered conditions for extended periods.
- Scattering Loss Reduction Dynamics: The environmental observation that contemporary Arctic sea ice has thinned and smoothed significantly over the past forty years, which crucially reduces acoustic scattering and enables long-range signal detection.
- CAATEX Framework: The joint international research methodology utilized to validate the efficacy of basin-wide acoustic thermometry in the modern Arctic environment.
Branch of Science: Physical Oceanography, Ocean Acoustics, and Climate Science.
Future Application: The technique will enable uninterrupted, year-round monitoring of underwater climate dynamics in polar regions. This observational capability will be critical for modeling sea ice melt rates, guiding navigation through newly accessible Arctic shipping routes, and assessing geopolitical and ecological impacts as energy resources become accessible.
Why It Matters: The Arctic Ocean is one of the Earth's most rapidly warming environments, yet it remains one of the least observed due to the impenetrable barrier of sea ice. Ocean acoustic thermometry provides an unprecedented, continuous method to monitor the ocean's interior, delivering the precise temperature data required to understand global climate shifts in a geopolitically critical region.
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| Photo Credit: Norwegian Coast Guard |
New research led by scientists at UC San Diego’s Scripps Institution of Oceanography finds that the travel time of underwater sounds traveling across the Arctic Ocean can be used to precisely measure ocean temperature under the region’s sea ice, providing precious data on temperature variability in a rapidly changing environment that is remote and difficult to access. The technique, known as ocean acoustic thermometry, was originally developed by the late Walter Munk and Peter Worcester at Scripps and Carl Wunsch at the Massachusetts Institute of Technology.
The basic principle leveraged by acoustic thermometry is that sound travels faster in warmer water and slower in colder water. The technique uses this relationship to infer the temperature of the water the acoustic signal passes through by measuring the time it takes the sound to travel from one point to another. The researchers tested the method during the 2019-2020 Arctic field season with the joint US-Norwegian Coordinated Arctic Acoustic Thermometry Experiment (CAATEX). The team used six bottom-anchored moorings across a roughly 2,600-kilometer (1,600-mile) path in the Arctic Ocean to transmit and measure acoustic signals every three days. The moorings spanned the Arctic Ocean, from north of Alaska in the west to north of Svalbard in the east, and remained in place for one year.
The experiment aimed to test whether this might be a viable way to measure Arctic Ocean temperature year-round, or if challenges such as the scattering of the sound by the rough undersides of sea ice might render the signals undetectable or impossible to decipher.
“The sea-ice has dramatically thinned over the past forty years and its roughness has also decreased,” said lead author Matthew Dzieciuch, a physical oceanographer at Scripps Oceanography. “We wanted to see if scattering losses have now decreased enough to enable acoustic propagation across basins by practical sound sources. And the conclusion is that it has.”
The researchers found that acoustic signals transmitted across the Arctic Ocean carried clear signatures of seasonal temperature changes in the water layers beneath the ice, demonstrating that the method can track ocean temperature variability year-round — even across distances exceeding 2,500 kilometers.
Because the Arctic’s sea ice blocks satellites’ views and makes access via ships challenging, these results point toward a practical way to continuously monitor temperature changes in one of the most rapidly warming and least-observed parts of the ocean. This warming and loss of sea ice coverage in the Arctic is also attracting attention from nations eyeing newly accessible shipping routes and energy resources, making tools that can monitor its ocean interior year-round even more geopolitically important.
Funding: The U.S. Office of Naval Research, the Research Council of Norway and the European Union Horizon Europe Programme provided funding for the fieldwork. The U.S. Defense University Research Instrumentation Program (DURIP) provided support for the development of the required instrumentation.
Published in journal: Journal of the Acoustical Society of America
Authors: Matthew A. Dzieciuch, Hanne Sagen, Peter F. Worcester, Espen Storheim, F. Hunter Akins, Stein Sandven, John A. Colosi, John N. Kemp, and Geir Martin Leinebø
Source/Credit: University of California, San Diego | Alex Fox
Reference Number: es033126_01
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