Marine Provinces

The effect of Plate Tectonics(Once again not a form of dubstep)

• This chapter is quite literally about the shape of the ocean floor. It has been created over billions of years by several processes. Perhaps the most influential has been Plate Tectonics.

I. Methods of measuring the ocean depths = Bathymetry.A. Soundings – Earliest means (85BC) of measuring ocean depth.

1. utilized a weight and rope.2. Depth was measured in fathoms

(6ft).

B. Echo soundings - Began in the early 1900s1. Eco sounder used sound “pings”

bounced off sea floor to measure depth.2. Accurate but not detailed.3. Recent Radar technology is improving

C. Satellite imaging – 1. Can “see” large areas of sea floor at one time.2. They can cover areas not yet mapped by ships (very slow).

3. The shape of the ocean surface itself reflects large features on the seafloor below.4. Typically combined with other Bathymetric techniques as resolution from space is low.

D. Seismic Reflection Profiles1. Low frequency explosion or gun sounds penetrate and bounce off sediment and rock differently.2. This Seismic Reflection Profile shows sediment layering (oil exploration).

II. Features of the Continental MarginsA. Ocean floor is divided into

1. Continental margins – shallow, close to continents.

2. Deep ocean basins – Deep, further from land.

3. Mid-ocean ridge – shallow, near middle of ocean (remember plate tectonics).

B. Continental Margins1. Passive vs. Active continental margins.

a. Passive margins – imbedded in the interior of lithospheric plate (not close to a boundary).

i. thick sediment accumulation.ii. Broad continental shelfiii. Little volcanic and earthquake activity.

b. Active Margins – Near lithospheric boundary.i. deep-sea trenches are commonii. Chains of islands commoniii. Lots of volcanic and earthquake activityiv. Thin sediment accumulation

C. Continental shelf – Generally flat zone extending from a passive shore.1. average width is 43 miles.2. many sediment features and islands located here.

D. Shelf break marks the boundary between the continental shelf and continental slope.

E. Continental Slope – steep slope between shelf and Abyssal plain.

a. Submarine Canyons are formed in the slope.

i. formed by erosion and turbidity currents.

F. Continental Rise – Pile of debris at the base of the Continental slope.1.Formed from many deep sea fans.

a. that is at the mouths of canyons.2. Function of erosion.

III. Deep-Sea ocean basin features.A. Abyssal Plains – Some of the deepest, flattest portions of the oceans.

1. Formed by suspension settling (fine particles) and cover ocean crust features.

2. Not many found in Pacific Ocean.a. Trenches near shelf act as a “gutter”

for debris.

3. Volcanic peaks of abyssal plaina. Abyssal hills are only visible in the Pacific because they have been covered by sediment in the other ocean basins (eg. Atlantic)

b. Sea mounts – volcanic peaks remaining under water but rising over 1KM above sea floor.c. Islands – Sea mounts that rise above the sea surface. example the Hawaiian islands.

4. Cold seeps and Methane Hydrates.a. support unique ecosystems free from sunlight energy.

5. Volcanic reef development.a. First a Fringing reef develops (coral) directly from shoreline.

b. Second. As volcanic island subsides (erodes) deeper lagoons are formed behind reef. Now it is a Barrier Reef.

c. Third. Coral grows above water level and island erodes below water. It is now an Atoll.-So first fringing reef, second barrier reef, third atoll.

6. Tablemounts – AKA Guyoutsa. Stage of subsiding volcanic Sea Mount after Atoll.b. Flat-top over 200m under surface.c. Reef (atoll) remnants remain but are too deep to be alive.

• IV. Mid-Oceanic ridges – A. Occupy about 30% of the ocean floor.

B. They are divergent boundaries where ocean basins grow – High volcanic activity1. This is an area where new lithosphere is produced (recall convection cells)

C. Divergent are different from Convergent ocean boundaries (deep-sea Trenches) where lithosphere is Destroyed.

1. incidentally these trenches have some of the steepest slopes in the ocean.

***Totally random bit of important information*** = A sediment-laden current that flows off of the continental slope is called a turbidity current.-As water picks up sediments on the continental shelf they become more dense and thus flow quickly down the continental slope after passing over the continental breaks and thus causing underwater avalanches that form the submarine canyons……. There you go.

The End