Uses

Sediment Thickness

  You may picture the seafloor as either sandy, or hard bottom and rather unchanging, but it’s more complicated. Much of the seafloor is covered in varying amounts of sediment. Total sediment thickness varies on a regional scale. It’s generally thicker and larger grained near the coasts and thinner and finer grained further out to sea. But ocean currents and seafloor topography (bathymetry) play a role in sediment thickness as well. Faster currents and steeper slopes typically mean less sediment. Sediment can also move, causing changes in sediment thickness and topography over time and space. The information below focuses on how sediment behaves on the continental shelf and slope.   So why should ocean planners pay attention to the sediment thickness data set?

  1. Considering sediment thickness is important for construction, seafloor cables, and pipelines. The layer of sediment on the seafloor directly influences the amount of energy required to reach hard substances to anchor objects like wind turbines. The thickness also matters for pipelines and cables buried under or laid on top of the sediment, since sand waves and megaripples are features in the sediment that can move and potentially leave a cable exposed or pipeline unsupported. In addition, sediment thickness can help predict the nature of submarine landslides, which can bend and break cables and pipelines. The thickness of the sediment also plays an important role in how much weight the seabed can support, including construction platforms and oil rigs, as well as how difficult it is to drive piles to support these structures.
  2. Sediment thickness is part of the story of seismic anomalies. The thickness of the sediment helps to better understand the history and tectonic plate stability of an area. This in turn leads to a more accurate prediction of seismic anomalies.
  3. Sediment affects the level of effort needed to obtain hydrocarbons. Hydrocarbons exist beneath the ocean seafloor, even beneath the hard bottom. The thickness of sediment affects the amount of effort it will take to reach the hard bottom and therefore reach the hydrocarbons.
  4. It’s an indicator of oceanic currents and other processes. Many research instruments are affected by oceanic currents and processes. These currents are affected both by the sediment thickness and other seafloor features in the same way that terrestrial winds are affected by mountains, buildings, and differences between tall grass and sandy plains.

Quick Caveats. This data set is meant to help planners begin to research sediment thickness. The data set has a very coarse resolution and therefore is limited in individual project applications. Planners may need to find a data set with higher resolution for their specific area. Lastly, just like the bathymetry data set, the sediment thickness data set was put together using a variety of sources and surveys. Caveats for these types of compiled data sets will apply.

Data-Source Experts
John King, Professor of Oceanography, Graduate School of Oceanography, University of Rhode Island

For questions, please contact info@marinecadastre.gov.