sea floor & sediments measuring the depths soundings echo sounder

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

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

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 500-600 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 2nd most common Shells & skeletons CaCO3 [calcareous]

SiO3 [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 18O:16O 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 85-180 million years old

Seabed Resources

Gas Hydrates Combo of natural gas (CH4) and water Ice-like structure

Seabed Resources

Manganese Nodules Manganese, copper, nickel & cobalt Cobalt is of particular interest