Exploring Oceans - A Level Geography (Geographical debates)

What are the main characteristics of the ocean?

Deep ocean basins, salinity, temperature and cold/warm ocean currents (as studied so far)

The oceans remain largely unexplored and yet are vital to life on earth. What percentage of the earths surface do oceans and seas make up??

71%

What percentage of the ocean is more than 3km deep?

50%

What percentage of the earths surface are made up from deep ocean basins?

50% of the earths surface

What are the five major oceans?

Pacific, artic, southern, Atlantic and Indian

Oceans and seas are ....

Interconnected

where is the deepest part of ocean?

The Mariana Trench which has a depth of 11 km in the biggest ocean of the Pacific

What is the key idea of this part of the chapter?

The worlds oceans are a distinctive feature of the earth

Oceans contain a dramatic landscape; what does this include?

Mountains the 'dwarf' the Himalayas and waterfalls bigger than Niagra and more active volcanoes than on land

All oceans have a similar structure; what are the stages of the ocean basin?

1) continent 2) continent shelf 3) continental slope 4) continental rise 5) seamount guyots 6) mid-oceanic ridge 7) abyssal plain

Where is the worlds largest underwater waterfall?

In the ocean beneath the Denmark Strait between Greenland and Iceland

1) continent and 2) continental shelf

The 1) continent gradually deepens across the relatively flat and wide 2) continental shelf

Average width = 70km with a slope angle of under 2m per km

2) continental shelf

Ends at the 3) continental slope where the slope angle increases at a much faster rate

70m per km

3) continental slope

Not continuous as submarine canyons and gullies are cut into it

On average the slope is quite narrow

It then gives way to the 4) continental rise

4) continental rise

Very wide and has a gentle gradient/slope

Unable to detect where the continental rise finishes and the abyssal plain begins (no data)

7) abyssal plain

Eventually the abyssal plain is reached which is the deepest part of the ocean (no data)

5) what are seamount guyots and where are they located?

They are areas of high relief and are isolated peaks that rise up (chains of mountains under the sea)

They are found in deep ocean basins which make up about 50% of the earths surface

They can climb over 3000m above the abyssal plain

Volcanic origin

Biggest seamount(s)

New England Seamount contains more the 30 peaks and has a length of 1600m

What is a seamount GUYOT?

Guyots are peaks which once rose above the ocean surface but over time have been eroded down by erosion and weathering leaving them often with a flat top

Guyots may have also reduced below sea level even more due to the weight of the guyot on the oceanic crust making it subside into the upper mantle

Why are seamount guyots not found as regularly in the Atlantic Ocean in comparison to the Pacific?

In the Atlantic Ocean, a large, thick accumulation of sediment from surrounding major rivers such as the Mississippi from the USA and the Amazon, Brazil and other rivers have deposited sediment on top of the guyots largely burying the peaks

THIS IS WHY IT IS EASIER TO IDENTIFY SEAMOUNTS IN THE PACIFIC AND NOT IN THE ATLANTIC - it does in-fact have many seamounts (former volcanoes) rising from the abyssal plain but they have become burried by sediment

What are 6) mid oceanic ridges?

Crossing the abyssal plains are very long chains of mountains which are called mid-oceanic ridges

They are landforms which are created at a divergent plate boundary

What angle do transverse faults (cracks) run at to along the ridges and how long are they?

90* so right angle and 1600km long transverse faults

What runs along the centre of a mid-oceanic ridge and what happens here?

Along the centre of a ridge a Rift Valley which is a deep notch with steep sides

Here magma rises up from the upper mantle along the Rift Valley and cools causing the crust/valley should be pushed apart

One side of the abyssal plain flows east and the other west (each moving about 1cm each year)

THIS PROCESS IS CALLED SEA-FLOOR SPREADING

What role does sea-floor spreading play?

It is of fundamental importance to the shape and size of the ocean basins and the position of land masses across the globe

Atlantic Ocean example

The Atlantic Ocean has opened and closed on several occasions during 'geological time' as convection currents powering the magma movements change

What happens as the magma cools?

As the magma cools the magnetic orientation of the poles is 'locked' in the iron particles in the new rock

Magnetic stripes of positive and negative stripes form either side of the ridges

It is known that the polarity of the earths magnetic field flips so that the north becomes the magnetic south (evidence = happens every 200,000 - 250,000 years)

What has research undergone on the magnetism of the cooling magma and therefore the surrounding rocks meant? And what does this indicate?

Research has identified symmetrical layers of magnetic stripes (positive and negative) either side of the ridges

These indicate the rate of sea-floor spreading

and paleomagnetism has provided important evidence to support the evolving theory of plate techtonics

What are some ocean basins characterised by?

some ocean margins are characterised by subduction zones

Here crustal plates are converging, which results in one which is forced down into the mantle

A feature of the ocean basin landscape at this point is a trench

What is an ocean trench?

a deep, underwater trough created by one plate subducting under another plate at a convergent plate boundary

Deepest places in the oceans varying between 7km and 11km

Water in the worlds oceans varies ..... and ......

Horizontally and vertically

When was the worlds first scientific investigation into the worlds oceans? + add detail

1872

HMS challenger from Portsmouth

3 years + vital to the understanding/beginning of oceanography and understanding the life in the sea

What are technological advances e.g through NASA allowing.?

It is allowing for more progress to be made in exploring the oceans

Since 2011, NASA has been using an Aquarian's satellite to observe salinity levels around the world

Salinity

Is a measure of the concentration of sodium chloride salt dissolved in water

It is expressed as grams (parts: ppt) of sodium chloride per 1000g of water

Fresh water = 0.5 ppt

Sea water average = 35ppt

Salinity varies with depth - the rapid change in salinity close to the surface is known as halocline

Variations in salinity influence water density and different densities affect water movements such as the flow of ocean currents that move heat from the tropics to the poles and affect global climate

Salinity cont

Variations in salinity influence density and when density changes in different layers of water

This impacts how, where and when water moves vertically in the oceans

As records/research of ocean salinity grows, it adds to our understanding of how the ocean operates and how oceans link to climate change

What is thermocline?

When water temperature rapidly decreases as depth increases close to the surface