Chapter 19-The Water Planet

Global Ocean:

• The body of salt water that covers nearly ¾ our Earth’s surface.

• Only Earth can be called the water planet—why is that so?

• No other known planet has this similar covering of water.

We have 5 major oceans:

• Atlantic-2nd largest ocean-3.9 km average depth.

• Pacific-largest ocean-1/2 of all ocean water that is on Earth and is the deepest at average depth of 4.3 km.

• Indian-3rd largest with average depth of 3.9 km.• Arctic-Smallest ocean & surrounds the North

Pole.(20 could fit in the Atlantic). Covered in ice most of the year.

• Southern Oceans-extend from the coast of Antarctica to 60 degrees S. latitude.

The Oceans

What is a Sea?

• A large, commonly saline body of water that is smaller than an ocean and that may be partially or completely surrounded by land.

• Examples: Mediterranean, Caribbean,Red Sea, and South China Seas.

Seas”

Features of the Ocean Floor

• The continental margins are shallow parts of the ocean floor that are made of continental crust and a thick wedge of sediment.

Continental shelf

• Most continents are outlined with shallow water that covers the edge of the continent. The part of the continent covered by water is the continental shelf. At the seaward edge is a steep slope called the continental slope.

Continental shelf:

Changes in sea level affect the continental shelves.

• Glacial periods-the ice holds large amounts of water so the sea level falls and exposes more of the continental shelf—this can be weathered and eroded.

• If the ice melts water is added and the sea level rises and covers the continental shelf.

Continental Slope:

• A steep slope. The boundary between the continental crust and the oceanic crust is located at the base of the continental slope.

• The ocean depth increases by several thousand meters within a distance of a few kilometers.

• See next slide. . . . .

Here you go----

What is happening at the slope?

• The depth greatly increases.

• Sometimes there are great deep V-shaped valleys—these are called submarine canyons.

Submarine canyons are often found at the mouths of major rivers

Turbidity currents:

• Are dense currents that carry large amounts of sediment down the continental slopes.

• These form when earthquakes cause underwater landslides or when a large sediment load runs down a slope.

Underwater landslide

Underwater slide:

Deep-ocean basin

• The part of the ocean floor that is under deep water beyond the continent margin and that is composed of oceanic crust and a thin layer of sediment.

• Will incorporate into Indian ocean.

Features of Deep Ocean Basins

• Broad flat plains; submerged volcanoes; gigantic mountain ranges; and deep trenches.

Trenches

• Long, narrow depressions located in the deep-ocean basins.

• Mariana Trench in western Pacific is the deepest place in Earth’s crust.

Abyssal Plains• Oceans about 4 km deep here.• Cover ½ of the deep-ocean basins

and are the flattest regions on Earth. Depths are from 3 m to over 1,300 km.

• Layers of sediment cover the bottom & are carried by ocean currents and wind brings some from the continents.

What else settles to the bottom?

• Organisms that live in the ocean and die.

How thick are the sediments?

• Determined by three things:– Age of the ocean crust. Older = thicker– Distance from continental margin to the

abyssal plain.– If the area is bordered by a trench. (thinner)

Mid-Ocean ridges

• These are the most prominent features of ocean basins. They form underwater mountain ranges.

Can mid-ocean ridges rise above sea level?

• Yes .. . . .Ireland is one area

Abyssal hill

• Fault-bounded blocks of crust that form parallel to the ridges as the lithosphere cools and contracts.

Fracture zones

• Ridges break into segments when plate motions change directions. This causes rough topography which runs perpendicular across the ridge.

Seamounts

• Any submerged volcanic mountain that is taller than 1 km.

• Form in areas of hot spots.• Seamounts that rise above the ocean surface form

oceanic islands.

Guyots

• These are seamounts that have moved with the tectonic plate away from the hot spot. The island sinks and is eroded by the waves to form flat-topped submerged seamounts.

• Before a seamount becomes a guyot, there is an intermediate stage. These are called “atolls”.

Guyot

Ocean floor sediments

• Rivers, shorelines, and dead organisms.

• Sediments are sorted by size.• Coarse gravel and sand are usually found close

to shore.• Why? They are heavy and do not move easily.

Where do they come from?

What about the lighter sediments?

• They remain suspended in water and are deposited at great distances from the shore.

• Sediments in the deep ocean basin (beyond the continental margin) are generally finer than those found in shallow water.

What is a core sample?

• Cylinders of sediment that are collected by drilling into sediment layers on the ocean floor.

• Sediments can be organic or inorganic.• Inorganic may be rock particles carried from land

by rivers.• Some may be fine particles of rock and volcanic

ash which may have been blown out by the wind.

What else provides sediments?

• Icebergs! They pick up rocks on their downward travels and when they break and drift to sea, melting occurs and debris drops.

What else can give up debris to the oceans?

• Meteorites-the cosmic dust that is left falls to Earth’s surface, hits the oceans and sinks.

Biogenic sediments

• This means the sediments were originally produced by living organisms.

Diatoms and radiolarians are microscopic organisms that leave silica sediments and foraminiferans leave calcium carbonate sediments.

Nodules

• Potato shaped lumps that form from substances that have dissolved and crystallized. Formed mostly from manganese, nickel, copper and iron.

• Commonly found on the abyssal plains.

Physical classification of sediments

• 2 basic types:

• Muds-very fine silt/clay-sized particles of rock. (red clay is very common)

• 40% of the ocean floor is covered with ooze.

• 2 types calcareous ooze and siliceous ooze

By the way, what is a continental rise?

• The continental rise is an underwater feature found between the continental slope and the abyssal plain. This feature can be found all around the world, and it represents the final stage in the boundary between continents and the deepest part of the ocean. The environment in the continental rise is quite unique, and many oceanographers study it extensively in the hopes of learning more about the ocean and geologic history

Continental Rise

Your Assignment• Using page 476-477 as a guide (9th grade book) draw a picture of

the ocean floor. Do your best work. Do this on a minimum size of 81/2 x 11 sheet of paper. It can be larger if you want.

• Label all the parts and number them as the list below shows:• On the back of your paper you will need to write the definition for

each of the parts: (1) Continental shelf; (2) Continental slope;(3) Continental rise; (4) Submarine canyon; (5) Abyssal plain; (6) Mid-ocean ridge; *(7) Guyot; and (8) Trench.

• You will also need do draw a (9) seamount, and (10) atoll. Draw these by the *(7)guyot to show the correct order of formation. Do not forget your definitions of each added onto the back of your paper or on another sheet and stapled to your drawing.

Due date is Thursday, Feb. 19th.