Features of the Seafloor

The Abyssal Plains

The deep seafloor, also called the Abyssal Plain, is located between the continental margins and oceanic ridges.  It's a pretty flat, featureless area covered in silt and clay-sized sediments.  Life is far and few between.  Most organisms are scavengers and decomposers, surviving on bits of dead creatures that have made their way to the bottom of the ocean.

image source:  "complexity1_600.jpg" by Deep East 2001, NOAA/OER is in the Public Domain

The abyssal plain is a poorly understood area.  At the beginning of this module, you watched two videos on the Okeanos Explorer.  Part of the Okeanos Explorer's goals is to study areas like these in order to gain a better understanding of how they work.  The Clarion-Clipperton Zone (CCZ) is located between Hawai'i and Southern California, and an expedition was launched in July 2018 to study this region.  You can learn more at the Deep CCZ Mission Overview page. 

Watch this video, "Exploring Abyssal Communities in the Pacific Ocean Before Deep Sea Mining Begins".   As you watch, note the following:

• • While there isn't a lot of organisms on the deepsea floor, there is a lot of diversity.
  • Did you know that there were plans to mine the deep seafloor?  Would you go do it?

Visit: Scientists Explore Biodiversity of Poorly Known Deep-sea Areas Targeted for Seafloor Mining to view this video.

When food does arrive on the abyssal plain, it's a feeding frenzy.  In June 2019, scientists exploring a shipwreck off the coast of Georgia & Florida and came across the remains of a dead 2.5 meters (8 feet) long swordfish.   As you watch, note the following:

• The seafloor is really flat, covered with silt & clay, with only a few sponges and coral scattered about.
• Why do you think a dead organism would envoke a feeding frenzy?
• Read more about this experience:  Dive 07: Oh My Grouper, Look at that Shark

Visit Dive 07: Oh My Grouper, Look at that Shark to view this video.

The Abyssal Hills

As you travel from the abyssal plain towards a ridge or a rise, hills appear adjacent to and trending parallel to the ridge axis. These are the Abyssal Hills, small volcanoes (extinct) or rock that has been faulted and pushed upward that have been covered by thick layers of pelagic sediments. They differ from seamounts in that abyssal hills are typically only 1,000 m in height, whereas seamounts are much taller.  Biodiversity and biomass are much greater on both as well, likely because rocks and other features common on seamounts and abyssal hills offer more protection than the exposed seafloor.