Hey there! I’m Kate from MinuteEarth. Did you know that in 1960, scientists did a cool experiment off the coast of Australia using explosives? Almost four hours later, the sounds from these blasts were picked up by underwater microphones near Bermuda, which is over 19,000 kilometers away! If these sounds had traveled through the air, they wouldn’t have gone nearly as far. Sound usually travels farther underwater because it loses less energy compared to when it moves through air. But how did these sounds travel such a long distance? It’s all thanks to an underwater sound superhighway!
This superhighway exists because sound travels at different speeds in different layers of the ocean. The speed of sound in water is affected by the water’s temperature and, to a lesser extent, its pressure. At the ocean’s surface, where the water is warm, sound moves quickly. But as you go deeper, the water gets colder, and the sound slows down. Around a thousand meters deep, the temperature stabilizes, and pressure becomes the main factor, causing the speed of sound to increase again.
The layer of the ocean where sound travels the slowest is also where it can travel the farthest. Imagine skiing: when you hit a slow patch of snow, you slow down and get pulled further into it. If you then hit a fast patch, you speed up and turn back into the slow snow. Sound waves do something similar. If they enter a slow layer of water at the right angle, they get trapped and bend up and down, traveling long distances without scattering or being absorbed. This special layer is called the “SOFAR channel.”
The SOFAR channel is not just a neat physics trick; it’s also very useful. Scientists think some whales use this channel to communicate over long distances. Monitoring systems in the SOFAR channel can detect sounds from all over the ocean, like the breaking of ice shelves. By measuring how fast sounds travel through this layer, we can track changes in ocean temperature, which is important for understanding our planet’s health.
The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) uses a network of hydrophones in the SOFAR channel to listen to ocean sounds. This helps them tell the difference between nuclear tests and other sounds, like whale calls. More than 180 countries support this effort, and the data collected is available to researchers worldwide. If you’re curious, check out ctbto.org to learn more. Thanks to CTBTO for supporting this video and working towards global safety!
Using materials like string, paper cups, and water, create a simple model to demonstrate how sound waves travel differently through air and water. Experiment with your model to see how sound travels faster and farther in water compared to air. Discuss your observations with your classmates.
Research the SOFAR channel and create a poster or digital presentation explaining how it works. Include diagrams to show how sound waves get trapped and travel long distances. Present your findings to the class and explain why this channel is important for marine life and scientific research.
Simulate whale communication using a classroom activity. Divide into groups and use different methods (e.g., tapping on desks, using low-frequency sounds) to send messages across the room. Discuss how whales might use the SOFAR channel to communicate over long distances and the challenges they face.
Conduct an experiment to observe how temperature affects the speed of sound. Use water at different temperatures and measure how quickly sound travels through each. Record your results and discuss how this relates to the layers of the ocean and the SOFAR channel.
Role-play as scientists from the CTBTO. Use maps and data to simulate monitoring ocean sounds for nuclear tests and natural events. Discuss the importance of global cooperation in monitoring and how this helps maintain world safety. Share your insights with the class.
Sure! Here’s a sanitized version of the transcript:
—
Hi, this is Kate from MinuteEarth. In 1960, scientists conducted an experiment off the coast of Australia, using explosives. Nearly four hours later, sounds from the blasts reached underwater microphones near Bermuda—over 19,000 kilometers away. In the air, these sounds would have traveled only a few dozen kilometers at most. Sound generally travels farther underwater because sound waves lose less energy moving through water than through air, but not by hundreds of times. These sounds traveled halfway around the world thanks to an underwater sound superhighway.
This superhighway exists because sound travels at different speeds in different layers of the ocean. The temperature of water—and to a lesser extent, its pressure—affects how densely packed its molecules are and how rigidly they are connected, which determines the speed of sound. At the surface, where the water is generally warm, sound moves quickly, but with increasing depth, the temperature drops, slowing the speed of sound. Around a thousand meters down, depending on your location, the ocean’s temperature levels off, and the effect of pressure takes over, causing the speed of sound to increase again.
Interestingly, the layer of the ocean where the speed of sound is slowest is also where sounds can travel the farthest. If you’ve ever skied, you might understand this concept; when you speed along a packed trail and then drift into a slower stretch of powder, your ski slows down, pulling you farther into the powder. If you then reach another packed trail, your outside ski speeds up, turning you back into the powder.
Sound waves behave similarly; if they enter a layer of water where sound travels particularly slowly at just the right angle, they can get trapped in that slow layer, bending up and down. Instead of scattering off the surface or being absorbed by the ocean floor, sounds in this layer get funneled along and can travel great distances. This layer, known as the “SOFAR channel,” may be a unique aspect of physics, but it’s also very useful. Based on whale behavior and calls, scientists believe some whales use the SOFAR channel as a long-distance communication method.
Monitoring systems in the SOFAR channel can detect sounds all over the ocean, from the breaking up of ice shelves to various other activities. Additionally, by using this infrastructure, we can calculate how fast sounds move through this layer of water; changes in the speed of sound in the SOFAR channel can help us track changes in ocean temperature—a critical measure of our planet’s health.
The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) uses a network of hydrophone triplets anchored in the SOFAR channel to monitor ocean sounds. This effort helps distinguish between nuclear tests and other sounds, such as the long-distance calls of whales. This work is supported by more than 180 member states, and the data collected worldwide is available to researchers looking to expand our knowledge about our planet. If you’re interested, please visit ctbto.org. Thanks to CTBTO for sponsoring this video and for their efforts in promoting global safety.
—
Let me know if you need any further modifications!
Sound – Vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear. – Example sentence: Scientists study how sound travels through water to understand how marine animals communicate.
Ocean – A large body of salt water that covers most of the Earth’s surface and surrounds its continents. – Example sentence: The ocean plays a crucial role in regulating the Earth’s climate by absorbing heat from the atmosphere.
Temperature – A measure of how hot or cold something is, typically measured in degrees Celsius or Fahrenheit. – Example sentence: The temperature of the ocean affects the types of organisms that can live there.
Pressure – The force exerted on a surface per unit area, often measured in Pascals or atmospheres. – Example sentence: As you dive deeper into the ocean, the pressure increases significantly.
Whales – Large marine mammals that are known for their intelligence and complex communication sounds. – Example sentence: Whales use low-frequency sounds to communicate over long distances in the ocean.
Monitoring – The regular observation and recording of activities taking place in a project or area. – Example sentence: Scientists are monitoring the ocean’s temperature to study the effects of climate change.
Distance – The amount of space between two points, often measured in meters or kilometers. – Example sentence: The distance sound travels in water can be affected by temperature and pressure.
Energy – The ability to do work or cause change, often measured in Joules. – Example sentence: The ocean is a source of renewable energy through waves and tides.
Channel – A path or route through which something can pass or be transmitted. – Example sentence: Sound travels through a channel in the ocean called the SOFAR channel, where it can move over long distances.
Global – Relating to the whole world; worldwide. – Example sentence: Global efforts are needed to reduce pollution and protect the ocean’s ecosystems.
