Ocean Sediments

There are two aspects of sediments that are important acoustically - the sediment thickness and the sediment type. We will be looking at the distribution of these two quantities in the world ocean.

Sediment Thickness

Below is a map of sediment thickness, the same one as in Figure 5.9 in your book (courtesy of NOAA).

Sediment Type

Sediments can be classified in several ways - either by size or source, as you read in your textbook, or by acoustical properties. The Naval Oceanographic Office has an extensive database of sediment types, and they use 4 different classifications -

  1. Enhanced: more than 400 different sediment categories. This is the actual database that NAVO maintains - the other 3 are derived or simplified from this.

  2. Standard: 30 categories based on grain-size and type. These categories fall into two broad classes -
    • Terrigenous: land-derived particles, primarily composed of silicate minerals, and
    • Carbonate: composed mainly of calcareous minerals created by marine organisms or marine chemical reactions.

  3. Reduced: reclassified based on grain size, corresponding to the Wentworth grain-size scale.

  4. HFEVA: 23 standard types based on grain-size and sediment mixtures. These types correspond to a set of 6 geoacoustic parameters that are inputs to a high frequency acoustic model. This classification should be used with caution as it is designed only for this purpose.

Let's have a look at two of these - the standard and the HFEVA for comparison.

The NAVO standard classification is shown below for the world ocean (sorry it doesn't include the Antarctic ocean!). The calcareous (marine derived) sediments are shown in cool colors; terrigenous sediments in warm colors. Click on any of the project regions to get a close-up view.

SOCAL region East Coast region Greenland-Iceland-UK gap South China Sea Yellow Sea / southern Sea of Japan

Below is the HFEVA data from NAVO. Click on any of the project regions to get a close-up view.

SOCAL region East Coast region Greenland-Iceland-UK gap South China Sea Yellow Sea / southern Sea of Japan

For more information, see the full description of the NAVO sediment type database is available here (word doc).