I am very excited to introduce Kim Martini as guest blogger here at DSN. Kim is a physical oceanographer working at the University of Alaska, Fairbanks and as the post reveals below is interested in deep-ocean waves. You can find her on Twitter at @rejectedbanana. Make sure to comment below and welcome her to DSN.

When asked what lies beneath the surface of the ocean, most people think of the various numbers of terrifying sea beasties that lurk there. But as a physical oceanographer, when I look at the ocean I think about completely different phenomena. I think about waves. And not just that puny Hawaiian surf that is often tossing professional surfers. These are the biggest waves in the ocean and they can’t be seen from shore. They exist inside the ocean. These waves are called internal waves.

If you are like most people (or even most marine scientists), you probably haven’t even heard of an internal wave. I didn’t even know they existed until I went to graduate school. In many ways they are similar to waves you see at the beach, they undulate, have crests and troughs, and even break! But since internal waves occur deep in the ocean rather than at the sea surface, they have some unique characteristics.

First, what is the difference between a surface wave and an internal wave? Both waves occur at the interface between two fluids of different densities, but these interfaces are different for the two waves. At the sea surface the interface is where air and water meet, two fluids with two different densities. Sea water becomes denser the deeper it is, and we can think of the ocean as being made up of an infinite number of tiny layers each having a different density. Between these infinite number of density layers are an infinite number of interfaces where internal waves occur.

Now that we understand that internal waves occur because density changes, why are they so cool? Here’s a short list: