Oceanography, notes, ocean, sea, continetal shelf, margin, rise, width, depth, temperature inversion, horizontal, vertical, minerals, polymetallic nodules, guyot, abyssal plain, poles, equator, latitude, surface

Oceanography: Relief features

• Continental Margin
• Ocean Floor Basin
• Oceanic ridge
• Trench

CONTINENTAL MARGIN:

• Continental Shelf – The continental plate which is partly submerged under the water. The shelf has a slope of less than 1° with a depth of 30-600m while width ranging from 0-70km. The shelf has an impact of wave erosion and this part is subsidies.

Features –

Continental shelf is narrower where high mountains are closer to the ocean. Narrower the continental shelf more natural harbour it makes for ship anchoring.

• Continental Slope – The part of continental plate which has a slope ranging from 2-5° and with a depth ranging from 500-1500m are called continental slope.

Features –

Submarine Canyon: Trenches present in slope having vertical walls are called submarine canyon.

• Continental Rise – The debris which gets deposited at the foot of the continental slope which is brought by certain rivers rose to certain height. The raised height feature is called continental rise.

Therefore, Continental Margin = Continental shelf + Continental slope + Continental rise

Advantages of Continental shelf:

• It is rich in biodiversity; both in heterotrophs and phototrophs because it is the photic zone i.e. sunlight penetrates.
• Rich in oil resources; either brought by river or fossil deposition by living organism
• Potential sites for economic minerals [20% of the world production of petroleumand gas comes from shelves. Polymetallic nodules (manganese nodules; concentric layers of iron and manganese hydroxides) etc. are good sources of various mineral ores like manganese, iron copper, gold etc]

OCEAN FLOOR BASIN

• Abyssal plain – The flat plain between the continental rise and the oceanic ridge is called abyssal plain.
• Sea Mount – Mountain rising from the sea floor but doesn’t reach the ocean surface are called sea mount. These sea mounts are volcanic in nature either active or dormant. Height up to 3000-4000km.
• Guyot – The surface of the sea mount is called Guyot. The flat surface is due to the subsidence which took place in the mountain. This Guyot is favourable for formation of atoll.

Source: www.pinterest.co.uk

 

• Ridge – The chain of mountain separated by the large depression due to the diversion of plate is called ridge.
• Trenches – The deepest part of the oceans formed generally near the converging plate boundaries which is also known as subduction zone are called trenches.
• Deep – The deepest point of the trench is called as deep.

 

TEMPERATURE OF THE OCEAN

Sources of Temperature: Sun, Volcanic eruption inside the ocean, radioactive material present inside the ocean

VERTICAL TEMPERATURE VARIATION

1. Thermal Layer (Epilimnion) – This layer varies from 0-500m in depth. This zone is also called as photic zone. This layer receives maximum sunlight and temperature varies from 0-25°C. Due to presence of sunlight it supports aquatic life. The temperature decreases with increase in depth.
2. Thermocline layer (Metalimnion) – This layer varies from 500-1000m. The rate of change of temperature is high. The temperature decreases rapidly as depth increases.
3. Dark layer (Hyplimnion) – This is the lowermost and darkest layer of the ocean. Here the temperature is uniform as no sunlight reaches here. Generally chemotrops are being found in this region.

 

Source: oceanmotion.org

 

Factors affecting vertical distribution of temperature:

• Offshore winds – When the sea winds move towards the land it takes away the warm water along with them. With the movement of the wind the upper part of sea becomes cool which leads to the condition of upwelling.
• Geometry of sea – If the sea is landlocked and no freshwater intake is there then the surface temperature of the sea will be much higher as compared to open sea.
• Submarine barrier – Those water bodies whose water circulation or mixing of water are hindered by the oceanic features like submarine barriers will have high temperature as compared to the sea which generally have ocean floors.

TEMPERATURE INVERSION

At equator – Due to heavy rainfall the temperature of the surface decreases, while the temperature of the layer below the surface is higher than temperature which is at the surface.

At poles – Due to higher latitude and flow of cold winds, the temperature of the surface is less than the temperature of the layer below the surface.

IMPORTANCE OF OCEAN TEMPERATURE

• It supports biodiversity in the photic zone and develop diversity in the flora and fauna of ocean
• Help in the growth of phytoplankton
• Provide favourable fishing ground
• Water current is developed which help in redistribution of heat on earth

 

HORIZONTAL TEMPERATURE VARIATION

It depends upon latitude, unequal distribution of land, prevailing winds

1. Latitude

Equator –

The temperature at the equator remains constant. During day time direct sunrays fall on equator and intense heat is there but as evaporation takes place the temperature comes down gradually. In the evening whole of evaporated water condenses and it rains, keeping temperature of the equator nearly constant.

 

Tropic of Cancer –

As we move horizontally upwards the sun rays become vertical at the topic of cancer. Due to this temperature of ocean increases.

 

Poles –

With further horizontal movement the sun rays become slant in the sub polar and the polar part because of which less heat reaches here and temperature of the ocean is very low.

 

2. Offshore Prevailing Winds

These are winds which are flows near the coastal region. These winds pickup the moisture from ocean surface because of which upwelling takes place. As upwelling brings cold water on the ocean surface it reduces temperature of the ocean surface.

 

3. Onshore Winds

Due to temperature difference and heating up of land and ocean at different temperature, the land breeze and sea breeze flows. When land breeze flows it increases the ocean temperature while sea breeze decreases temperature of the ocean.

 

4. Current

The current are the large water mass movement with a fixed temperature. This movement impacts the ocean temperature in the region where it flows.

E.g. Gulf Stream is warm water current and it makes the temperature of USA coastal region higher as compared to the temperature of ocean gyre region.

 

5. Geometry of Water Body

If the water body is open for influx of fresh water the temperature will be less but if water body is enclosed and no influx of freshwater takes place then temperature of that water body is higher.