Oceanography Ch 3

What are oceanic rises?

part of MOR -have slopes gentler less rugged than oceanic rises. (spreads faster, less tectonic activity and chance to develop) ex. East Pacific Rise- gentler

what is the mid atlantic ridge?

part of Mid ocean ridge in N Atlantic Ocean.

What is the Mid Ocean ridge

results from sea floor spreading along divergent plate boundaries -continous fractured looking mountain ridge extending along through all ocean basins "seams of baseball" -covers 23% of earths surface!

What is bathymetry?

(bathos=deep, metry= measurement) a measurement of ocean depth and the charting of the shape, or topography of the ocean floor. *Involves measuring vertical dist from ocean surface down to mountains, valleys, and plains on sea floor.

What modern technology do we use today to map the sea floor and measure bathymetry?

*Multi bean echo sounders- use multiple freq of sound at once -these have a wider range (60km), high resolution 3D images -ship emits multiple beams of sound from both sides of hull, echoes return to recievers and computer interprets to create data about depth, shape, and composition of seal floor -However, still spreads and gets weaker with distance, so limited in deep areas. *Side-scan sonar (sound navigation and ranging) -towed behind ship to produce detailed strip map with gap right below where instrument is, of coean floor bathymetry. -get photo-like images-can detect objects. -unfortunately is expensive and time-consuming process, "moqing the lawn" *Seismic reflection profiles- oceanographers use air guns to produce strong, low freq sounds- these sounds penetrate BENEATH ocean floor. -reflect off boundaries between diff rock sediment layers= seismic reflection profile. **Currently, we use satelitees to map ocean floor.- using gravity- sea floor features directly influence earths gravitational field - deep areas have lower gravitational attraction -large undersea objects like seamounts exert gravitational pull. - differences affect sea lvl cause ocean surface to buldge outward, inward mimicking relief of ocean floor **these images arent perfect, but much higher res

What two types of continental margins are there?

*Passive- embedded within the interior of lithosperic plates, not close to any plate boundary -usually lack major tectonic activity. -features include: continental shelf, continental slope, continental rise that extends outward toward the deep ocean basins *Active margins- are assoc with lithosperic plate boundaries and have a high degree of tectonic activity. -Two types: 1) Convergent active- assoc with oceanic-continental convergent plate boundaries. -features: from land to ocean: on-shore arc of volcanoes, narrow shelf, steep slope, and an offshore trench that delineates plate boundary Ex: E Coast of US- where no plate boundary is. 2) transform active- less common, assoc with transform plate boundaries. -offshore faults parallel main transform boundary fault-create linear islands, banks, and deep basins close to shore. (ex Coastal California by San Andreas Fault)q

Ocean exploration vehicles

*manned subermisbles -alvin 1964, 3 ppl, 72hrs, max 14,800ft robotic arms, for hydrothermal vents, titanic -rovs- remotely operated vehicles-controlle from ship, 4,000 m, fiber optic cables = limits *teacher drove for 2 seconds, monterey! -Auvs- autonomous underwater vehicles ie.e underwater gliders, comp programmed, buoyancy and wings propel through h20, energy efficient, up/down motion-sawtooth profile, satellite connection, take data: salinity, depth, etc. goes up to surface to transfer data and back down.

what are submarine canyons?

-Narrow, deep valleys V shaped profile, have branches with tributaries with steep to overhanging walls.- like canyons on land *found in continental slope mostly, some shelf. *turbity currents may be responsible for formation-underwater avalanches-triggered by earthquakes, oversteeping of sediment accumulation on shelf, passing hurricanes, rapid input of sediments from waters.

What three major provinces are part of the ocean floor?

1) continental margins-shallow water areeas close to continents 2) deep ocean basins- deep water areas far from land 3) mid ocean ridge- made of shallower areas near middle of ocean *plate tectonics help form these provinces. - sea floor spreading = mor and deep ocean basins created -contints spliting apart = new contintental margins

What was the next method for determining bathymetry, when did it come about?

1900s- the invention of an echo sounder (or fathometer) *Sends out ping from ship into ocran, produces echoes and bounces off any density. The time it takes for the echo to return would be the depth. **The problems are: it lacks detail, may detect submarines or fish, and it fans out as it moves forward into the ocean and gets weaker.

What is a rift valley?

Along center of MOR crust, downdrop, created by sea floor spreading (rifting) where two plates diverge. -one rift valley along MOR is 20 mi wide and 2 mi deep! -molten rock presses upward toward sea floor during rifting process, setting ff earthquakes, creaeting jets of superheated water, eventually solidifying into new oceanic crust. *central rift valley commonly has cracks/fissures/faults, earthquakes occur here caused by injection of magma into sea floor or rifting along faults.

What is the coninental slope?

Beyond shelf break, wjere deep ocean basins begin. avg angle from shelf to ocean basin- passive or trench - active is 4 degrees.

How/when was the echo sounding method improved?

During WWII it was discovered echo sounders could detect submarines! -They worked to improve the technology and came up with the PDR (precision depth recorder0 in 1950's -Uses high freq sound beam to measure depths to resolution of about 1m or 3.3ft. -1960's produced reliable maps of ocean floor we have today to help support idea of sea floor spreading and plate tectonics.

What is one of the earliest forms of measuring bathymetry?

Line soundings- used first in Meditteranean Sea by Posidonious 85 B.C. *Crew let out line before heavy weight on end of line touched bottowm- measurements are fathoms: (fathme=outstrechted arms) about 1.8m or 6 ft. **But has problems, the boat movement and feeling bottom make this not very accurate. -Like trying to get surface topography of earth from blimp in foggy night with rope and heavy weight..

What are the oceanic ridges?

Segments of the MOR -they have prominent rift valley and steep, rugged alops (spreads slower more development and tectonic activity) ex. Mid Atlantic Ridge- rugged

What is the continental shelf?

The general flat zone extending from shore beneath ocean surface until increased slope angle occurs at SHELF BREAK. -underlying rock is granite, so shelf is part of continent -type of margin determines features/shape of shelf. ie.e passive = usually larger, mostly flat active= shorter, usually with volcanoes, islands, shallow banks, deep basins etc.

What are the abssyal plains?

feature of deep ocean floor beyond continental margin (shelf, slope, rise). -Flat depositional surfaces, slops less than fraction of degree cover extensive parts of deep ocean basins. -avg 4500 m (15000ft)- 6000 m (20,000) ft -formed by fine particles of sediment slowly rifting onto deep ocean floor -mill yrs, thick blanket of sediment created by SUSPENSION SETTLING as fine particles "marine snowww" accumulate on ocean floor -cover most irregularities of floor over time -sediment traveling from turbidity currents adds to this load. **type of cont margin determines distribution of abyssal plains -few in pacifiv ocean, most in atlantic and indian -DEEP OCEAN TRENCHES found in PACIFIC PREVENT SEDIMENT FROM MOVING PAST SLOPE. dist also between cont margin and floor of ocean basins so great, sediment settles before reaching these regions. - however, passive margins of atlantic and indian, turbitidty currents travel directly down cont margin into abyssal plains.

What are the hydrothermal vents of the MOR?

in central rift valley- *They are sea floor hot springs created when cold sea water seeps down along cracks, fissures in ocean crust and approaches underwater magma chamber. -water picks up heat and dissolved substances and works its way back toward surface through complex plumbing sys. -exits through sea floor -temperature of water out of hydrovent determines appearance out of the chimneys- *Warm water vents- <30 degrees C, emit clear water *White smokers- 30-350 degrees C, emit white water (sulfides) *Black smokers- >350 degrees C, emit black water ( metal sulfides) ***no steam because pressure keeps in liquid form. *The hydrothermal vents carry with them an unusal deep-ocean ecosystem that can survive w/o sunlight! -huge tubewroms, large clams, mussels and others -survive off of chemoautotrophes that metabolize the hydrogen sulfide gas released by the chimneys.

What are the volcanic features of the MOR?

in central rift valley- *pillow lava/pillow basalts- when lava flows from tall volanoes (seamounts) and spills into sea water, it is cooled and forms these pillow like rounded lobes of rock. *80% of earths volcanic activity is on sea floor Hydrothermal vents

What is the continental rise?

transition zone between the cont margin and deep ovean floor compromised by huge pile of debris. -turbidity currents suggest material transported is responsible for creating cont rises. -turbitity currents move through/exit sub canyon, slope angle decreases, turbidity current slows- suspended material settes in distinvtive layering=GRADED BEDDING- grades in size upward, large pieces settle first eventually to very fine pieces. *turbidite depositis, turbitidty currents leave layer, next one comes and leaves one on top etc etc. *deposits at mouth of sub canyons are fan-shaped, called DEEP SEA FANS. They create cont rise as merge together in passive however, at convergent active margents, steep cont slope leads into trench where sediments accumulate and there is no rise.