week 2-ave Flashcards
what is bathymetry?
the study of ocean floor contours
how do we know what the ocean floor looks like?
bathymetry
what does bathymetry do?
- measures the depth of the ocean
- illustrate maps of ocean floor
what is depth sounding and why was it inaccurate?
- lowering of the rope with a weight
inaccurate:
- only measures single point of the ocean floor
- is very slow
- impact of pressure that squashes the rope and gives an artificially short measurement
why is lidar not used to measure depth of ocean floor?
-Lidar can’t penetrate water very well
-contour maps are used instead
what are the 3 S’s of bathymetry?
- sonar
-satelite
-seismic
what are marine provinces?
specific regions of the ocean that relate to the geography of the ocean floor
divergent boundary and 2 examples
- where plates are moving apart (such as mid ocean ridges)
-ex. Mid Atlantic Ridge
-ex. East Pacific Rise
convergent boundary and example
- ## where plates are moving together, such as deep-ocean trench (one has to move under the other)
why do we get mountain building with convergent boundaries?
they do not want to go under each other because they have the same density
what is sonar bathymetry and what are limitations?
-bouncing sound down to the ocean floor & measuring it)
-any biological life will interfere and it takes a lot time
echosounding vs side scan echosounding
-echosounding uses hull mounted (bottom) beam to get image or sea floor bathymetry
-side scan sonar instrument is towed behind a boat, has a wider profile but there is a data gap directly below the instrument
Satellite bathymetry
-ideal, not always possible, more $$
- measures the water surface not the ocean floor and can detect changes in the surface of the ocean like water displacement
-can quickly measure same areas over and over again
Seismic bathymetry
-uses lower frequencies & strong signals
-one boat makes sound source, other boat measures seismic reflection
-delay in signals determines depth
what are the 3 main parts of the ocean?
- mid-ocean ridge
2.deep ocean basin - continental margin
mid-ocean ridge
interconnected mountain chain along divergent plate boundaries (longest mountain chain in world)
continental margin
dynamic, interaction of water running off land and into the ocean
what is marie tharp’s contribution to mapping mid-ocean ridges?
-used data from german ship that took 14 profiles of the south atlantic
-she was the first to map the unseen topography of the ocean floor on a global scale
-proved mid-ocean ridges exist:
what was mary tharp’s evidence?
- if two land masses drifted apart they would leave a gap (mary drew deep v like parts)
-where there were ocean ridges there were earth quakes
-the pattern of scars = evidence of continental drift
how much of the earth’s surface is mid-ocean ridges?
23%
why does the North West Mid Ridge Channel occur/why is it unique?
This deep sea canyon is unique because cold dense water goes down & the accumulation of the coldest water = cold surface water creates perfect line channel through millions of years of flow
difference between oceanic ridge & oceanic rise?
- rate of spread (rise moves faster)
-spreading faster so it does not have time to profile, it is much flatter
How old is the east pacific rise and mid atlantic ridge
EP- 30 million years
MAR- 100 million years
what is the tallest mountain?
Mauna Kea (tallest from ocean floor to peak)
transform faults
-feature of plate boundaries
-where plates move in opposite directions
-seismically active
fracture zones
-intraplate feature
-plates move in the same direction at a slightly different rate
-less seismically active than transform faults
hydrothermal vents
-feature discovered in east pacific rise
-home to unique life forms (extremophiles)
- black & white smokers and minerals found here
white smokers
-barium
-calcium
silicon
-250-300 degrees celcius
black smokers
-metal sulphides present
-350 degrees celcius
what do vents do?
-sea water moves through a plumping system and is converted to hydrothermal fluid
-extreme temperature profile changes causes massive turbulence and energy changes
chemosynthesis
extremophiles and other life forms get energy from heat not sun
abyssal plains
- Flat, most featureless areas of the Earth
- even less features than deserts
- nearly 50% of planet is covered in them
why do abyssal plains exist?
they exist because of sediment and their distribution is influenced by continental margin type
abyssal hills
-elevated areas on plains
-isolated or in group
-volcanic origins
types of abyssal hills?
seamounts
guyots or tablemounts
seamounts
-circular/elliptical feature
- less than 1000m in height
- relatively steep slopes
guyots or tablemounts
-flat topped
-eroded by wave action at the ocean surface
how are seamounts formed?
- by hotspot volcanism (rise of a hot buyant mantle)
- rise as tectonic plates moves over hotspot
- extremly hot part of the mantle = less dense bc its hotter = it rises and pushes against the lithosphere (oceanic plate), which generates new mount
seamoAunts and bio productivity?
- high level of biological productivity because with the upwelling of cold water filled with minerals and pulling warm water down = more life
active margin (and features)
- narrow shelf
-steep continental slope
-earthquakes, volcanos, mountain building
-coincides with plate margins
-california, chile
-(seamounts, trenches)
passive margin (and features)
-wide continental self
-longer transitional to oceanic crust
-little earthquake & volcanic activity, no mountain building
-does not coincide with plate margins
-louisiana
- (abyssal plains)
features of passive margin
- thick accumulation of sediment
-transitional crust, subsiding, faulted continental crust - shelf
why are sediments important? (5 reasons from lecture)
- contain a record of Earth’s history & provide clues
- marine organism distribution
-paleoclimatology
-climate change
-circulation patterns
what is sediment?
- particles of organic or inorganic matter that accumulate in a loose, unconsolidated form
four types of sediment?
- lithogenous
- biogenous
- hydrogenous
- cosmogenous
lithogenos sediment
terrigenous - from land- inorganic
biogenous sediment
remains of marine organisms
ex. shark teeth
- important in deep ocean areas
- close to 50% of planet is made up of this type of sediment
hydrogenous
- precipitated chemicals from sea water
-dissolved materials/metals - water is a universal solvent that carries these minerals = chemical reaction that pulls material out from solid material
cosmogenous sediment
from space
processes of sedimentation
- erosion (weathering)
- transportation (ex. areas with big rainfail changes clarity/turbidity and picks up sediment)
- deposition
sediment deposition layers?
sediment layers can be km thick above oceanic and continental crust
why are larger grains closer to land? (like quartz and glass looking sediment?)
- the bigger the grain the more energy required to transport it = why they are closer to land
neritic
- derived from land, larger grained
pelagic
derived from sea, fine grained
neritic lithogenous sediment
- deposited within or near continetal margins
-wave action transports sediments
deposition
- accumulating sediments and growing
- occurs in low energy environments
- protected areas will have more deposition
erosion
-losing materals
-weather
-high wave activity
- high energy areas have less deposition and more erosion
pelagic wind blown sediment
- wind blown (aeloian) sedient from desert
- big wind events generate disposition
- trend viewed = areas that are really dry blow sediments, not in wet areas at they stick together
biogenous sediment & marine ooze
tests of microscopic organisms are important component of marine ooze (testa = shell)
what is an ooze?
-very fine-grained pelagic sediment containing at least 30% biogenous test
-calcarous or siliceous
-toothpaste consistency
how do we know some places of land used to be oceanic crust?
-biogenous evidence found in hardened ooze on land
-silliceous or calcareous deposit
distribution of calcareous sediment
- why do we not see it everywhere in pelagic zone = at really deep depths, calcium carbonate dissolves so it accumulates in more shallow areas
calcite compensation depth *recommend to look at graphs on slides to study as well-lecture 2 of week 2
-CCD is depth where all CaCO3 is dissolved
-as you go down in the ocean respiration happens a lot deeper than photosynthesis happens
- deep, cold, water = holds more gas = lets carbon dioxide accumulates and dissolves calcium carbonate
- this is why we do not get calcium carbonate on the surface’s of very deep parts of the ocean
How does calcium cabonate (CaCO3) deposit in places below the CCD line (not at surface but below)?
- due to seafloor spreading
-as the sea floor weathers away the particles get trapped by the plate boundaries and sillica deposits protect them until the sea floor weathers away
why does silliceous ooze accumulate?
-cool waters and upwelling
-sillica-secreting organisms live in sunlight surface waters and ooze only accumulates beneath areas where productivity & secretion is high
- when the rate of supply of siliceous tests is greater than the rate at which sillica dissolves = ooze accumulates
ocean sediment
-mostly consists of lithogenous and biogenous
-more fine-grained sediment is transported with ease by current, wave, wind
- large particles need big energy to be moved and can take over 50 years to settle (clay)
how do we measure marine sediments?
-sample = clamshell samplet (no depth but easiest)
-collect a core = piston core (drilling to seafloor)
-sediment traps
