Physical Geography 4 Flashcards
Hydrological cycle
The hydrological cycle, is the circulation of water within the earth’s hydrosphere in different forms i.e. the liquid, solid and the gaseous phases.
Hydrosphere
The hydrosphere is the sum of all water on Earth, including water in the oceans, lakes, rivers, and in the air
Distribution of water in different sources
71% oceanic 29% fresh water in glaciers and icecaps, groundwater sources, lakes, soil moisture, atmosphere, streams and within life.
Oceans of the world
The geographers have divided the oceanic part of the earth into five oceans, namely the Pacific, the Atlantic, the Indian, Southern ocean and the Arctic.
Major Oceanic relief/ division of ocean floor
four major divisions: (i) the Continental Shelf; (ii) the Continental Slope; (iii) the Deep Sea Plain; (iv) the Oceanic Deeps.
Continental Shelf
1.area between the beach and shelf break, ends typically in a steep continental slope. The continental shelf is the extended margin of each continent occupied by relatively shallow seas and gulfs.
2.It is the shallowest part of the ocean showing an average gradient of 1° or even less.
3.The average width of continental shelves is about 80 km. almost absent or very narrow along some of the margins like the coasts of Chile, the west coast of Sumatra, etc. On the contrary, the Siberian shelf in the Arctic Ocean, the largest in the world,
4. The depth of the shelves also varies. 30m- 600 m.
5. The continental shelves are covered with variable thicknesses of sediments, and over a long time by the continental shelves, become the source of fossil fuels.
Continental Slope
1.The continental slope connects the continental shelf and the ocean basins. It begins where the bottom of the continental shelf sharply drops off into a steep slope. Signifies end of continental plate and beginning of oceanic plate.
2.The gradient of the slope region varies between 2-5°. The depth of the slope region varies between 200 and 3,000 m.
3. Canyons and trenches are observed in this region.
Deep Sea Plain
Deep sea plains are gently sloping areas of the ocean basins. These are the flattest and smoothest regions of the world. The depths vary between 3,000 and 6,000m. These plains are covered with fine-grained sediments like clay and silt.
Oceanic Deeps or Trenches
These areas are the deepest parts of the oceans. The trenches are relatively steep sided, narrow basins. They are some 3-5 km deeper than the surrounding ocean floor. They occur at the bases of continental slopes and along island arcs and are associated with active volcanoes and strong earthquakes. Formed by convergent plates and subduction.
Minor Relief Features
Ridges, hills, sea mounts, guyots, trenches, canyons, etc.
Mid-Oceanic Ridges
A mid-oceanic ridge is composed of two chains of mountains separated by a large depression. The mountain ranges can have peaks as high as 2,500 m and some even reach above the ocean’s surface. Iceland, a part of the mid- Atlantic Ridge, is an example. Formed by floor spreading and cooling of lava.
Seamount
It is a mountain with pointed summits, rising from the seafloor that does not reach the surface of the ocean. Seamounts are volcanic in origin. These can be 3,000-4,500 m tall. Often the vents of volcanoes. The Emperor seamount, an extension of the Hawaiian Islands in the Pacific Ocean, is a good example.
Submarine Canyons
These are deep valleys, some comparable to the Grand Canyon of the Colorado river. They are sometimes found cutting across the continental shelves and slopes, often extending from the mouths of large rivers. The Hudson Canyon is the best known submarine canyon in the world.
Guyots
It is a flat topped seamount. They show evidences of gradual subsidence through stages to become flat topped submerged mountains. It is estimated that more than 10,000 seamounts and guyots exist in the Pacific Ocean alone.
Atoll
These are low islands found in the tropical oceans consisting of coral reefs surrounding a central depression. It may be a part of the sea (lagoon), or sometimes form enclosing a body of fresh, brackish, or highly saline water.
Factors Affecting Temperature Distribution of oceans
The process of heating and cooling of the oceanic water is slower than land.
(i) Latitude:the temperature of surface water decreases from the equator towards the poles because the amount of insolation decreases poleward.
(ii) Unequal distribution of land and water : the oceans in the northern hemisphere receive more heat due to their contact with larger extent of land than the oceans in the southern hemisphere.
(iii) Prevailing Wind:the winds blowing from the land towards the oceans drive warm surface water away form the coast resulting in the upwelling of cold water from below. It results into the longitudinal variation in the temperature. Contrary to this, the onshore winds pile up warm water near the coast and this raises the temperature.
(iv) Ocean currents : warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas.
Thermocline
Boundary separating surface water from deeper waters and there is a rapid fall of temperature below it. 90% water below thermocline.
Vertical Distribution of Temperature
Temperature of ocean and middle and low latitudes is 3 tiered.
1. 0-500m with temperature 20-25 degrees, always present in tropical region but in mid latitude only in summer
2. Thermocline layer 500-1000 m- rapidly decreasing temperature
3. Very cold, with temperature upto 0 degrees
In High latitudes i.e. polar region, water from surface to bottom 0 degrees.
Horizontal distribution of Temperature
Average temperature 27 degrees, decreases from equator to poles. The oceans in the northern hemisphere record relatively higher temperature than in the southern hemisphere. The highest temperature is not recorded at the equator but slightly towards north of it. All this due to uneuqual distribution of land and water. The average annual temperatures for the northern and southern hemisphere are around 19° C and 16° C respectively.
Salinity
amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater. It is usually expressed as parts per thousand (o/oo) or ppt.
Factors affecting ocean salinity-
(i) The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
(ii) Surface salinity is greatly influenced in coastal regions by the freshwater flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
(iii) Wind, also influences salinity of an area by transferring water to other areas.
(iv) The ocean currents contribute to the salinity variations. Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of water in an area.
HORIZONTAL DISTRIBUTION OF SALINITY
The salinity for normal open ocean ranges between 33 o/oo and 37 o/oo.
1. The salinity variation in the Pacific Ocean is mainly due to its shape and larger areal extent. Salinity decreases on the western parts of the northern hemisphere because of the influx of melted water from the Arctic region. In the same way in the south, it decreases.
2. The average salinity of the Atlantic Ocean is around 36 o/oo. Sub tropical region with high evaporation, low rainfall. The North Sea, in spite of its location in higher latitudes, records higher salinity due to more saline water brought by the North Atlantic Drift. The Mediterranean Sea records higher salinity due to high evaporation. Baltic Sea, Black Sea records low salinity due to influx of river waters in large quantity.
3. The average salinity of the Indian Ocean is 35 o/oo. The low salinity trend is observed in the Bay of Bengal due to influx of river water. On the contrary, the Arabian Sea shows higher salinity due to high evaporation and low influx of fresh water.
Vertical Distribution of Salinity
Salinity changes with depth, increases. The lower salinity water rests above
the higher salinity dense water. At the surface changes because of 4 factors discussed previously.
Halocline
Point in ocean after which salinity sharply increases.
Types of movement of ocean water
Horizontal (currents and waves), vertical (tides)
Ocean currents and waves define with difference
continuous flow of huge amount of water in a definite direction while the waves are the horizontal motion of water. Water moves ahead from one place to another through ocean currents while the water in the waves does not move, but the wave trains move ahead.
