1.a. the world's oceans are a distinctive feature of the Earth.

Name the world's major oceans

• Arctic

• Mediterrenean

• Gulf of Mexico

• Caribbean Sea

• Atlantic

• Southern ocean

• Indian ocean

• Pacific

• South China Sea

• Bering Sea

Area and volume of Pacific

• Area: 155.6 million km²

• Volume: 622 million km³

Area and volume of Atlantic

• Area: 76.8 km²

• Volume: 300 million km³

Area and volume of Arctic ocean

• Area: 14.1 km²

• Volume: 17 million km³

Area and volume of South China Sea

• Area: 2.3 million km²

• Volume: 4 million km³

Area and volume of Gulf of Mexico

• Area: 1.6 million km²

• Volume: 2.4 million km³

The relief of ocean basins

They are highly varied and often dramatic landscapes

Continental shelf definition

The shallow, gently sloping submerged edge of a continent

Continental shelf formation

• Starting at the edges of the continents, the water gradually deepens across the relatively flat, wide margin of the continental shelf

• The continental shelf is geologically and tectonically part of the continent and is exposed or submerged as sea level changes over time

Continental shelf - PSD

• Average width is 70km

• Slope angle is just under 2m per km

Continental slope definition

• The edge of the continental shelf where the slope angle increases to a much faster rate (70m per km).

• It marks the transition from continental crust to oceanic crust

Continental slope PSD

It extends from 200m to up to 4,000m in depth

Abyssal plain definition

• Deepest part of the ocean

• Vast, flat expanses that make up half of the Earth's surface

How does abyssal plain form

Sediment accumulates over millions of years, covering irregularities in the oceanic crust

Ocean ridges definition

• Long underwater mountain chains with a central rift valley in some areas

• They are often found in the middle of oceans

Ocean rifts - formation

They form at constructive plate boundaries where magma rises as plates move apart - This creates new oceanic crust

Where are ocean rifts found

They are found in the middle of ridges as steep-sided notches

Key features of ocean rifts

• They produce heated water and minerals

• The mid atlantic rift valley is 15km wide in some places

The mid atlantic ridge - formation

• Constructive plate margins occur when 2 plates move away from each other and new crust is created at the boundary

• North American and Eurasian plates are pulled apart by convection cells

• As the plates diverge, molten rock or magma rises from the mantle to fill any faps

• In doing so this creates new oceanic crust

• The ridge is 3km high from the ocean floor in places

• Transform faults occur at right angles from the main plate boundary

• Rift valleys can also be formed which is an area of down faulting between parallel faults

Ocean trenches - definition

• Long, narrow, deep depressions in the ocean floor

• Deepest parts of oceans

• Mariana Trench is an example

How do ocean trenches form

At destructive plate boundaries, one oceanic plate is subducted beneath another or a continental plate

Seamounts definition

• Chains of volcanic mountains and isolated peaks, some rises over 3,000m above the abyssal plain

• They do not reach the ocean surface

How do seamounts form

Magma rises through the oceanic crust, often above hotspots or at plate boundaries, creating a volcanic mountain

Guyots definition

Flat topped peaks that once rose above the ocean

How do guyots form

• A volcanic seamount originally rises above/near sea level

• Wave erosion flattens the ridge

• As the mount moved along the plate away from the ridge, the mount subsides below the level of the sea (sea floor spreading)

• A seamount maintains a volcanic shape

• At the peak of the guyots, evidence of coral reefs can be found which indicates there former shallow sea existence

Key features of guyots

• They show how sea levels change

• They have high levels of biodiversity

How to map the ocean floor

• Scientists began mapping the ocean floor in 1920s

• They used echo sounders, which utilise sonar technology

• The sonar showed that the ocean floor has dramatic physical features such as mountains and canyons

Material of the ocean crust

It is a thin layer of volcanic rock called basalt