Ocean Floor Flashcards
What were the 3 old assumptions about the ocean?
- oceans were basically bowl or trough like “basins”
- following (1) the greatest thicknesses of sediment would be predicted to accumulate at centre
- oceans + continents btwn them are permanent features that have remained unchanged since Earth formed
How was the ocean floor mapped?
- depth originally measured by lowering weighted lines overboard
- echo sounder (aka sonar) was invented as a primary instrument for measuring depth by reflecting sound waves from ocean floor
- multi-beam sonar developed later (using an array of sound sources + listening devices for mapping narrow swaths of seafloor)
- later came use of satellite radar altimeters (used to record seafloor topography by bouncing micro waves off sea surface)
what was the seafloor topography like?
- huge ridges (oceanic or mid-ocean ridges), originall assumed to have been very deep
- deepest areas were through like areas (deep sea trenches that bordered major landmasses
- Suken, inactive volcanoes (seamounts) in linear patterns
What are abyssal plains?
huge expanses of relatively flat, sediment-covered (nearly featureless) regions of deep ocean floor (btwn ridges + trenches) called abyssal plains
What is a continental shelf?
continental margins, a submerged, shallow-water platform extended seaward for significant distances
- at other margins, continental shelf appear very narrow or even non-existent (esp where bordered by a deep sea trench)
what is the seafloor covered with?
sediment
- areas most distant from land, deep sea sediment is largely biochemical
- accumulation of ooze
minor:
- mud (from windblown dust)
- chemical sediment produced by precipitation of minerals from seawater
What is ooze
accumulation of microscopic skeleton of planktonic organisms
What are the sediment input from land?
- closer to continental landmasses, clastic sediment derived from land sources cover the shallow-water continental shelf (transported by waves + offshore currents)
- also forms thick accumulations at continental rise (at base of steep continental slope) onto parts of flat abyssal plain
What are turbidity currents?
down-slope movements of dense, sediment-laden water (often triggered by earthquakes)
Where are turbidity currents commonly focused?
in steep-walled submarine canyons cut into the continental slope
What is the sediment deposited by a turbidity current
turbidites: layered + commonly exhibit graded bedding (decreasing in sediment grain size from bottom to top due to settling of progressively finer-grained sediment)
what is a submarine fan?
the accumulation of land-derived sediment on the continental rise (thin out on the abyssal plain) and in trenches
What are the types of continental margins
- passive continental margins
- active continental margins
what is a passive continental margin?
- wide continental shelf
- geologically quiet (“passively” accumulate sediment)
what is an active continental margin?
-continental shelf is narrow or non-existent
- associated w/ deep sea trenches
- geologically active (associated w/ earthquakes + volcanic activity)
What surprise did the study of mid-oceans ridges bring?
- basalt (mafic volcanic rock) exposed at crests of mid-ocean ridges (indicate formed recently)
- sediment thickness found to increase away from crests of ridges (+thickest in trenches)
What are seamounts
submerged volcanoes
- appeared to form chains
What is the relationship of seamounts with distance?
- ages of seamounts increase w/ increasing distance from Hawaii
- seamounts become more deeply submerged further away from Hawaii
What are atolls
- ring-shaped reefs w/ central lagoon
- commonly associated w/ submerged seamounts
- constructed primarily from skeletal remains of corals + other organisms
Where are atolls formed
forms on flanks of a sinking volcanic island
(hypothesis proposed by Charles Darwin)
What is ocean circulation
Idea that ocean circulations is driven by water salinity + temperature differences
Basic idea:
- warm, less salty, low-density seawater flows at surface toward poles
- cold, more salty, high-density water flows along seafloor toward equator
What is a Thermohaline Cirulation
- cooler, saltier water, is dense enough to sink to seafloor
- cold, salty deep current flows southward toward equator to connect to surface water current
- conveyor works as “circuit”
What did Alfred Wegener challenge about the configuration of oceans + continents
he claimed continents + ocean were distributed very differently in the deep past - continents “drifted” over time
What did Wegener name the larger landmass of all the continents?
Pangaea (“all land”)
