Ask an Explorer

Questions answered during the expedition are below.

 


 

Question from:Audrey, Palo Alto, CA

How do underwater earthquakes affect animals?

Answer from: James Connors, Web Coordinator, NOAA Office of Ocean Exploration and Research; Steve Ross, Research Professor, University of North Carolina-Wilmington

Most studies of submarine earthquakes are focused on geological processes such as subduction zones and the generation of tsunamis, therefore little is known about the biological effects.

Earthquakes on land and undersea displace a lot of sediment, which in the marine environment could result in benthic fauna such as corals, anemones, sea stars, urchins, crustaceans, bottom fish, and others being buried or disturbed. These events could also potentially create new seafloor structures and hard features for marine animals to eventually inhabit. The amount of noise generated by an earthquake could also be damaging to animals, particularly the marine mammals that use sound to navigate and communicate.

The biggest threat of submarine earthquakes for people and animals is the tsunamis they can potentially generate. Tsunamis are events of huge-wavelength waves that pass through the deep ocean causing little disruption, but cause sea levels to rise violently upon reaching shallow water. Tsunamis can be devastating for animals in a shoreline or intertidal community, just as they are for humans living along the coast.

 


 

Question from: The Leitch Family, Charleston, SC

In Rachel Carson's The Sea Around Usz, she writes about the "reflective layer" and offers a few hypothesis circulating at the time (50s). With the current technology, has the reflective layer been identified? If so, what is it?

Answer from: Steve Ross, Research Professor, University of North Carolina-Wilmington

In the early days (during and immediately after World War II) of developing sonar equipment used to take depth soundings, people began to notice a layer between the surface and the bottom that reflected some of the sound energy. It almost looked like a false bottom, except the layer reflected a more diffuse, thick signal. In addition, as people examined this layer in more detail, they noticed that it moved, and it moved in a predictable fashion - upward at night and back down during the day, where it hovered in the mid-water column. Very curious. It was soon called the Deep Scattering Layer because it scattered the sonar signals.

Determining what was causing this was of vital importance to the U.S. Navy (and others) because of the need to understand how to interpret different sonar signals - submarines from whales, undersea mines from shipwrecks - a very difficult task in the early days of sonar development. This phenomenon triggered a variety of research, much of it using mid-water sampling nets to tow through this layer at all times of the day.

The answer soon became clear: this layer, which occurs all over the world in the open oceans, is composed of huge numbers of small fishes, shrimps, plankton, and squids. In fact one member of this community, the diminutive bristlemouth (Cyclothone spp.) may be the most abundant vertebrate on Earth. These animals undergo daily migrations in order to feed. At or near sunset, they move from great depths (about 400-600 meters) to more shallow depths (even all the way to the surface in some cases) where they feed on plankton and other animals. Near sunrise they move back down to their deep-water habitats where they rest and float until the next migration. This world-wide migration is one of the most amazing and extensive animal movements on the planet.

Today, after decades of research, we know a lot about the timing of these migrations, which animals are doing them, and how far they travel. There is still a lot to discover about what impact this abundant community has on oceanic productivity and the movement of nutrients around the oceans.

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