Chapter GEO307 4
I. Measuring depths a. Hand line (wire marked w/ fathoms, w/ lead weight on end [fathom = 6 ft]) b. Echo sounder depth recorder c. LADS (Laser Airborne Depth Sounder) uses light instead of sound in shallow water d. Satellites use gravity's effect on sea surface e. Multi-beam sound systems (i.e. side-scan sonar system/swath bathymetry) allows for 3D contouring Unique Ocean Features a. Greatest canyons (Challenger Deep) b. Greatest vertical rise (Hawaii) c. Greatest mountain ranges (mid-ocean ridge) Continental margin area of continental land mass present below sea level a. Active margins (Pacific) narrow & steep b. Passive margins (Atlantic) broad & shallow c. Continental shelf i. Geologically part of continent ii. Exposed in past glaciations iii. Variable width (averaging 65 m) iv. Depth at edge about 130 m v. Sediment accumulation from various sources d. Submarine canyons formed during lower sea levels, extensions of modern rivers i. Powerful turbidity currents carry sediment extremely quickly ii. Material sorted (turbidites deposited sediment) Abyssal plain/ocean floor a. Abyssal plain flattest plains on Earth b. Abyssal hills (<1000 m high) c. Seamounts steep-sided volcanoes d. Guyots flat-topped seamounts e. Coral reefs i. Darwin's hypothesis of atoll formation correct ii. Sequence of reefs formed by volcanic movement f. Ridges/rises spreading centers g. Trenches deepest spots in ocean Sediments
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Thickets layers near continental margin Thinnest layers at spreading centers Formed by particles settling to sea floor Provides biological history, important for understanding Earth's history Rates of deposition i. Neritic faster than pelagic ii. River estuaries are faster than quiet bays which are faster than continental shelf (all faster than pelagic sediments) iii. Correlates to age of floor (oldest = most sediments) except at convergent boundaries f. Sediment sources i. Terrigenous from sediments terrestrial source (volcanoes, weathering of rocks, dust inputs, etc.) ii. Lithogenous sediments pre-existing rock (type of terrigenous sediment) iii. Biogenous sediments formed from remnants of living organisms 1. If >30% biogenous, termed ooze 2. Calcareous calcium carbonate a. Soluble in seawater at depth b. First starts to dissolve at lysocline (slight increase in acidity at this depth) c. Carbonate Compensation depth depth at which calcium carbonate <20% 3. Siliceous silicate a. Soluble everywhere b. Most soluble in shallow water iv. Hydrogenous sediments formed by chemical actions of seawater (carbonate precipitation from seawater, phosphorites, salts, manganese nodules) v. Cosmogenous sediments origins from space (meteorite debris); rare, usually dissolve; present in all sediment 1. Tektites Earth material that have been melted by meteorite impact g. Sampling sediments i. Dredge big steel bag dragged along bottom to collect big rocks ii. Grab samplers go down, open/close, & collect sediments iii. Corer long metal tube that collects a length of sediments iv. Acoustic profiling uses sound to profile sediments by penetrating them Paleoceanography sediments as records of change
a. b. c. d. e.
VII.
a. Long term changes in climate cause changes in surface ocean plant/animal community b. Changes in types/composition of sediments at particular spot c. Changes in biological composition i. Identifies species in sediments ii. Typical of a particular set of conditions d. Stable isotopes ratio in shells/corals indicates water temperature/sea level changes Seabed resources a. Manganese nodules metal-rich lumps sitting on/in sediments i. Internal rings changes in chemicals during formation ii. Grow much slower than sedimentation rate iii. Areas of slower sedimentation rate b. Methane hydrate "flammable ice" i. Methane potential, future energy source ii. Global climate iii. Sediment strength