you're reading...

Book Review

Ringing in the New Year

Happy 2016 all you Oceanbiters! Starting this year, we, the bloggers, have decided to change things up a little bit. Each month we will be devoting one week to a particular ocean-related theme. Every post during that week will cover a different aspect of that theme. We’ve got a bunch of cool ideas to get the ball rolling, but we’re always looking for suggestions. If you’ve got a topic you want to hear more about, let us know via Facebook or Twitter! To start things off, we will be “Ringing in the New Year” with a series of posts about sound in the ocean.

Long time readers may have noticed how often acoustics comes up in the study of the ocean. This is no coincidence and there are a myriad of reasons why. The most basic, however, has to do with the physics of sound.

Sound is a kind of wave that moves energy through a medium (ex. air, water, solids, etc). In particular, sound propagates as a longitudinal, or compression, wave. This means that sound gets from one place to another by vibrating molecules in the direction it is traveling. A slinky makes for a great illustration. Imagine that you stretch the slinky between your hands. If you move one end back and forth, the coils expand and contract along the axis of the slinky. If you instead move one end of the slinky up and down, the whole thing wiggles like a snake. A longitudinal wave is analogous to the first situation.


Figure 1: An illustration of longitudinal, or compression waves. The sphere in the center expands, compressing the molecules near its surface. Those molecules, in turn, press on the molecules nearest them. The process repeats itself as the wave expands outwards. (Animation courtesy of Thierrey Dugnolle via Wikipedia).

Check out the animation in figure 1 for another example: The circle in the center expands, compressing the particles that touch its surface. The resulting change in pressure pushes on the next set of particles. The process repeats itself as the wave expands outward. This is kind of like how your stereo works. The speaker vibrates, pushing on the air nearby. The sound wave expands and eventually makes it to your ear.

Since sound is a compression wave, the speed at which it propagates depends on the density of the material it is traveling through. Generally, the denser the medium, the faster sound can travel. Consider the difference between air and seawater; at sea level, air has a density of ~1.2 kg/m3 while seawater is ~1025 kg/m3. Likewise, the speed of sound in air is 343 m/s. In seawater, sound travels at about 1500 m/s.

The difference between the density of air and water is quite stark. More subtle changes in the density of seawater cause an incredible phenomenon known as the SOund Fixing And Ranging, or SOFAR, channel (which is definitely a name an engineer came up with). The SOFAR channel is a layer of seawater where the sound speed is at its lowest level, as shown in figure 2. Sounds can get “trapped” in the channel and propagate thousands of miles before fading away. This happens because the sound waves will get refracted, or bent, back toward the middle of the channel when they hit regions of higher sound speed (for a more detailed description of how this works check out the resources at DOSITS and NOAA Ocean Explorer).


Figure 2: An example of a sound speed profile from a patch of ocean north of Hawaii. The y-axis is depth and the x-axis is the sound speed. Note that the sound speed is faster at the surface and at the bottom. The minimum occurs at about 750 m deep. That is where the SOFAR channel is this particular part of the ocean. (Figure courtesy of Nicoguaro via Wikipedia)

The SOFAR channel is a pervasive feature in the world’s oceans. By simply placing a hydrophone (or underwater microphone) in it, oceanographers can study all kinds of interesting things. Marine biologists can study whales by listening to their calls from thousands of miles away. Physical oceanographers use it to measure the temperature of huge amounts of deep ocean water. The U.S. Navy has even used the SOFAR channel to monitor Soviet submarines during the Cold War.

The use of acoustics in oceanography is not, however, limited to the SOFAR channel. Scientists have also developed acoustic systems to map the sea floor, track large groups of fish, and probe the Earth’s structure beneath the bottom of the ocean. These methods are used for everything from primary research to ecosystem monitoring and beyond.

For the rest of the week, you’ll get an in depth look at some of the wonderful results – and unforeseen consequences – from using sound in the ocean. Tomorrow, Austen will cover an article discussing the use of autonomous robots for monitoring fish populations. Wednesday is a double header: Megan will look at whale earwax and how that affects their perception of sound. Gordon will discuss a paper on how fish can find the sounds they are interested in amid all the subsurface noise. On Thursday, Valeska will describe a study of how fish use sound at multiple stages of their life cycle and how those processes are affected by ocean acidification. Sarah will wrap up the theme week on Friday with a story about how seismic surveys may be affecting sea turtle behavior and distribution.

We hope you enjoy this new endeavor of ours! We’ve certainly had fun putting it together. And, as always, keep checking back after the theme week for all the latest in the oceanographic literature. Happy New Year and many happy returns!



  1. […] the 1996 Acoustic Thermometry of Ocean Climate (ATOC) study. The program placed a source in the SOFAR channel – the layer of the ocean where sound propagates most efficiently – just off Hawaii. […]

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 9 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 10 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 11 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com