Sea Floor & Sediments Measuring the Depths Soundings Echo Sounder
Measuring the Depths Modern Tools ROV’s LADS Side-scan Sonar Satellites
Sea Floor Bathymetry
Continental Margin Active margin Leading margin Pacific-type Convergent boundary Continental shelf is narrow and irregular
Continental Margin Passive margin Trailing margin Atlantic-type Divergent boundary Sediment build-up on shelf
Continental Shelf
Formation
Shelf Break & Slope
Submarine Canyons
Turbidity Currents Turbidites
Continental Rise Atlantic, Indian, and Antarctic Oceans Not usually found at active margins
Ocean Basin Floor
Abyssal Hills & Seamounts Abyssal hills Most common topographic feature < 1000m Seamounts Steep-sided volcanoes > 1000m
Abyssal Hills & Seamounts Guyots (gee-ohs) Flat-topped seamounts
Coral Reefs
Trenches
Sediments Rate of accumulation Distribution Source & abundance Chemical composition History
Particle Size
Size & shape Influences sinking rate and travel time
Particle Size Particle aggregation Electrical attraction Fecal pellets 2200x
Location Neritic Continental margins & islands Pelagic Found on the deep sea floor
Location
Rates of Deposits Neritic Sediments Highly variable River estuaries Quiet bays Relict Sediments
Rates of Deposit Pelagic Sediments Slower than neritic m
Source & Chemistry 4 sources: 1. Preexisting rocks 2. Marine organisms 3. Seawater 4. Space
Lithogenous Sediments Terrigenous sediments Fine to coarse Most common Weathering of rocks Transport by rivers, winds, volcanoes and glaciers
Lithogenous Sediments Terrigenous sediments Dominant neritic sediment Clear size distribution
Lithogenous Sediments Pelagic lithogenous sediments Abyssal clay 70% clay-size particles 0.1 cm per 1000 years! Red clay Due to oxidation of iron
Lithogenous Sediments 4 types of clay minerals: 1. Chlorite
Lithogenous Sediments 4 types of clay minerals: 2. Kaolinite
Lithogenous Sediments 4 types of clay minerals: 3. Illite
Lithogenous Sediments 4 types of clay minerals: 4. Montmorillonite
Biogenous Sediments Fine to coarse 2 nd most common Shells & skeletons CaCO 3 [calcareous] SiO 3 [siliceous] Oozes
Biogenous Sediments Coccolithophorids Pteropods Foraminfera Lysocline
Carbonate Compensation Depth The depth at which the amount of calcareous material preserved falls below 20% of the total sediment
Biogenous Sediments Diatoms Radiolarians
Hydrogenous Sediments Derived from chemical reactions in the water
Hydrogenous Sediments Carbonates Limestone-type deposits Shallow, warm water Ooliths
Hydrogenous Sediments Phosphorites Phosphorus in the form of phosphate Continental shelf & slope
Hydrogenous Sediments Salts High rate of evaporation in shallow areas Carbonate salts, sulfate salts, then chlorides
Hydrogenous Sediments Manganese nodules Manganese, iron, nickel, cobalt & copper
Cosmogenous Sediments Sediments derived from space
Lithification Formation of sedimentary rock Temps <200ºC
Diagenesis Chemical changes of sediments when they react with seawater
Sampling Methods Dredges Large bulk samples Benthic organisms
Sampling Methods Grab samplers Mud & sand Quantitative sampling
Sampling Methods Corers Gravity corer 1-2 m cores
Sampling Methods Corers Piston corer Up to 20 m cores
Sampling Methods Corers Box corer Large, undisturbed samples Door
Sampling Methods Platform drilling JOIDES Resolution 1100 m cores
Sampling Methods Acoustic profiling
Sediments as Historical Records Paleoceanography Chemistry of biogenous sediments Ratio of 18 O: 16 O Proportion of these in skeletons reflects abundance of isotopes in water
Seabed Resources Sand & Gravel Annual world production = 1.2 billion metric tons Only significant seabed mining done in the US
Seabed Resources Phosphorite Mined to produce phosphate fertilizers Substantial source in Onslow Bay, NC
Seabed Resources Sulfur Used for production of sulfuric acid
Seabed Resources Coal Produced by burial of plant material in areas of low oxygen Peat
Seabed Resources Oil & Gas Represent >95% of the value of all resources extracted from the sea floor Sedimentary rocks million years old
Seabed Resources Gas Hydrates Combo of natural gas (CH 4 ) and water Ice-like structure
Seabed Resources Manganese Nodules Manganese, copper, nickel & cobalt Cobalt is of particular interest