Chapter 4 The Sea Floor and Its Sediments

4.1 Measuring the Depths Methods for measuring depths: Hand line and wire marked with fathoms, with a lead weight on the end Echo sounder, or depth recorder Laser airborne depth sounder (LADS) Satellites

Boxed Reading: Bathymetrics Lead line vs. multibeam sound systems Side-scan sonar system Swath bathymetry

Side – Scan Sonar

4.2 Bathymetry of the Sea Floor Continental margin Continental shelf Continental shelf break Continental slope Continental rise Ocean basin floor Abyssal plain Abyssal hills Seamounts Guyots Fringing reefs Barrier reefs Ridges, rises, and trenches Plate tectonics

World wide Continental Shelves

Field Notes: Giant Hawaiian Landslides Giant landslides Blocks or rock: 30 km x 5 km x 2 km Frequency of occurrence Several per million years Posed important hazard Scientific research Identifying the causes Predicting the next giant landslide

4.3 Sediments Particle size Classification Horizontal transport and sorting Location Classification: neritic or pelagic Rates of deposit Processes and variability Source and chemistry Lithogenous sediments Biogenous sediments Hydrogenous sediments Cosmogenous sediments

Sediments: Sources  Lithogenous sediments – Come from rocks, erosion, examples: sand, boulders, gravel, silt  Biogenous sediments- comes from organisms’ remains. Diatomaceous (diatoms) chalk.  Hydrogenous sediments- precipitate out of water.  Manganese nodules  Cosmogenous sediments – Comes from space  Meteorites, comet dust, etc.

4.3 Sediments, continued Patterns of deposit on the sea floor Processes and patterns Climatic variations are recorded in layered sediments Formation of rock Sedimentary rock Metamorphic rock Sampling methods Dredges, grab samplers, a corer, and acoustic profiling Sediments as historical records Distribution and isotopic composition of skeletal remains

4.4 Seabed Resources Sand and gravel Sand and gravel, calcium oxide, calcium carbonate, tin, iron, platinum, gold, and diamonds (currently mined) Phosphorite Phosphate fertilizer (not currently mined) Sulfur (no longer mined) Coal (currently mined) Oil and gas (currently extracted) Gas hydrates (not mined) Methane and water

4.4 Seabed Resources, continued Manganese nodules Manganese, copper, nickel, and cobalt (not currently mined) Sulfide mineral deposits (not currently mined) Relatively little is known about these deposits to determine their economic importance Laws and treaties 200-mile economic zones International treaties

Summary Methods for measuring ocean depth Bathymetric features Continental shelf, slope, and rise Ocean basin floor Seamounts and barrier reef formation Sediment classification Size, location, origin, and chemistry Biogenous sediments Siliceous and calcareous sediments Carbonate compensation depth (CCD) Sediment sampling methods Calcareous biogenous sediment cores Used to study climate change

GEN – to make or create, comes from, the beginning or source