Chapter 3

Marine Provinces

bathymetry

measurement of ocean depths and the charting of shape, or topography of ocean floor. determining bathymetry involves measuring vertical distance from ocean surface down to mountains, valleys, plains on sea floor.

how are most ocean floor features generated

plate tectonic processes, and different sea floor features exist in different oceanographic locations

underwater features

deep trough, ancient volcanoes, submarine canyons, great mountain chains.

what are the three major ocean provinces

continental margins, deep ocean basins, mid ocean ridge

how do we measure bathymetry

soundings, posidonius made first sounding in 85 BC. line with heavy weight 2km long. used for 2000 years.

fathom

standardized unit of measure. 1.8 m, 6 feet

HMS challenger

made first systematic measurements in 1872. Deep ocean floor has relief, variations in sea floor depth.

echo sounders

sends a signal (ping) into the ocean. bounces off any object that is a diff density than seawater. like a radar on land.

when was the mid atlantic ridge discovered

in 1925 by a german ship named meteor.

pdr

precision depth recorder. made in 1950,s focused high frequency sound beam to measure depths to a resolution of 1 m. produced first reliable sea floor maps.

how wide are sea floor echo sounder strips

60 km, 37 miles wide

side scan sonar

can be towed behind ship to provide detailed bathymetric strip map. detailed image of seabed.

satellite mapping

measures sea floor features based on gravitational bulges in sea surface. dips (trenches) have lower gravitational attraction. bulges and seamounts have higher gravitational attraction.

seismic reflection profiles

provide information about structures beneath sea floor. strong, low frequency sounds produced by explosions or air guns. detail ocean structure beneath sea floor.

passive continental margins

not close to any plate boundary, no major tectonic activity (earthquakes, volcanoes, mountains)

active continental margins

associated with convergent or transform plate boundaries. lots of tectonic activity. transform active margin, san andreas fault.

convergent active margin

oceanic continent convergent plate boundaries. active continental volcanoes. narrow shelf, offshore trench, W. S. America (Nazca plate subducted beneath S. A. Plate

Transform Continental margin

less common, transform plate boundaries, linear islands, banks, deep basins close to shore. Coastal california along san andreas fault.

continental shelf

flat zone from shore to shelf break (where increase in slope angle stops). featureless bc of marine sediment. average slope of 1/10 of a degree. topography =coastal region of continent. underlying rock is granitic continental crust.

continental shelf features

type of continental margin determines shelf features. passive margins have wider shelves, CA’s transform active margin has a continental borderland (high degree of relief, islands, shallow)

continental slope

where deep ocean basins begin. topography similar to land mountain ranges. slope>continental shelf. averages 4 degrees, varies 1-25. marked by submarine canyons

submarine canyons

narrow, deep, v shaped. steep to overhanging walls. extend to base of continental slope. 3500 m below sea level. carved by turbidity currents.

turbidity currents

underwater avalanches mixed with rocks and other debris. dislodged sediment mixes with water as it moves down slope under influence of gravity to produce a turbidity current. flow of dense fluid is erosive and cuts a gully in the slope.

continental rise

transition btwn. continental crust and oceanic crust. marked by turbidite deposits from currents. graded bedding in turbidite deposits coarser at bottom. deposits generate deep sea fans.

abyssal plains

base of continental rise to deep ocean basins. some of deepest flattest parts of earth. (without bottom is what it translates to). average btwn. 4500-6000 m. suspension settling of very fine particles.

Atlantic ocean abyssal plain

most are in the atlantic ocean. deep ocean trenches in Pacific ocean prevents sediment from moving past continental slope.

abyssal plain volcanic peaks

poke through sediment cover. below sea level there is seamounts, tablemounts, guyots. abyssal hills or seaknolls are less than 1km above sea floor.

ocean trenches

deep linear scars in ocean floor caused by collision of two plates along the convergent plate margin.

volcanic arc

chain of volcanoes, hundreds to thousands of miles long. forms above a subduction zone

island arcc

curved chain of volcanic islands at tectonic plate margine, with deep ocean trench on convex side.

continental arc

volcanic arc at a topographic high region along a continental margin

pacific ring of fire

occurs along margins of pacific ocean. where majority of world’s active volcanoes and earthquakes occur.

mid ocean ridge features

longest mountain chain, covers 23%. Global mid ocean ridge is continuous fractured submarine mountain range that extends through the middle of all ocean basins for some 75,000 km.

how above the surrounding sea floor is the mid ocean ridge

1\.5 miles

what does the mid ocean ridge originate from

completely volcanic in origin. lava of basaltic composition. along the crest is a central down dropped rift valley created by sea floor spreading processes. small shallow quakes. lots of fresh lava flow.

pillow lava

“pillow basalt” shapes formed when hot basaltic lava cools quickly. smooth rounded lobes of rock resembling stacked pillows.

ridge vs rise

ridge is mountainous with steep irregular slopes and oceanic rises where slopes are gentler. differences in overall shape between ridges and rises are due to spreading rate differences. oceanic ridges have slower spreading rates than oceanic rises.

hydrothermal vents

sea floor hot springs, foster unusual deep ocean ecosystems able to survive without sunlight

warm water vents

temps below 30 degrees C

white smokers

temps from 30-350 degrees C. emit white water because of light colored substances like BaS

black smokers

temps above 350 degrees C. black colored metal sulfides, FeS, NiS, CuS, ZnS

transform faults

along mid ocean ridge to counteract spreading zones. causes: to accommodate spreading of a linear ridge on spherical earth. different segments spread apart at different rates. seismically active zone

fracture zones

along pacific ocean mid ocean rise. seismically inactive, occur beyond offset fragments of rise. are ancient, inactive fault scars embedded within a plate.

where are transform faults found

between ridge axis and denote a plate boundary

where are fracture zones found

outside of the ridge axis and have a vertical scar with the younger portion at a higher elevation than the older portion of the same plate. transform faults are plate boundaries, fracture zones are intraplate.

what are the three types of oceanic islands

1. those associated with volcanic activity along mid ocean ridge
2. associated with hot spots (hawaiian islands)
3. island arcs associated with convergent plate boundaries.