Goh Cheng Leong Chapter 12: The Oceans YouTube Lecture Handouts

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Watch Video Lecture on YouTube: Goh Cheng Leong Chapter 12: The Oceans

Goh Cheng Leong Chapter 12: The Oceans

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  • Oceans: 70% or 140 million square miles area is comprised by oceans – source of food and tides for power

  • Challenger was the 1st successful worldwide deep sea expedition

  • Oceanography: Science of oceans and deep seas

  • Most famous International Oceanographic Research Center is International Council for Exploration of Sea with its headquarters in Copenhagen

  • Ocean exploration for observation and recording is an expensive affair – which involves specially equipped vessels in mid oceans for long period

  • Older echo-sounding techniques have been replaced by radar sounding and electrical echo devices to find depth and map relief of oceans. Also grog-men equipped with breathing apparatus are involved

  • Deep sea core samples obtained by boring for study of oceanic deposits (oozes, muds and clays). Automatic recording thermometers and sensitive instruments can be lowered to any depth by stationary vessels

  • To measure current flow – use of propellers, vanes and pendulum is done

  • Sealed bottles and floating objects to report precise time and place of discovery to compute rate and direction of rift and current flow.

Relief of Oceans

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Watch Video Lecture on YouTube: Exploring the Layers & Depth of Ocean: Introduction to Oceanography

Exploring the Layers & Depth of Ocean: Introduction to Oceanography

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Image of Relief of Oceans

Image of Relief of Oceans

  • Continental Shelf: Seaward extension of continent from shoreline marked by 100 fathom isobaths (contours marking depth BSL) – shallow platform with width varying greatly. In mountain areas of Rockies and Andes, it may be absent. Angle of slope is least when continent shelf is widest. Most common gradient is 1 in 500. It is regarded as part of continent submerged due to rise in sea level.

  • Shallowness enables sunlight to penetrate through the water and encourage growth of plants – rich in plankton and are richest fishing grounds in world – Grand banks off Newfoundland, North Sea and Sunda Shelf

  • Limited depth and gentle slope keep out cold under current and increase height of tides (might hinder shipping). Greatest seaports like Southampton, London, Hamburg, Rotterdam, Hong Kong are on continental shelves

  • Continental Slope: Abrupt gradient change 1 in 20

  • Deep Sea Plain: Lies 2-3 miles BSL and cover 2/3rd of ocean floor. Once thought featureless, it has plateau, ridges, trenches and basins in midst of oceans – Azores and Ascension Island

  • Ocean Deeps: Long narrow trench to a depth of 5000 fathoms or 30,000 feet. Found close to continents in Pacific Ocean (greatest is Mariana Trench near Guam Island around 36,000 feet deep). Others are Mindanao Deep, Tonga Trench & Japanese Trench in Pacific Ocean

Ocean Deposits

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Watch Video Lecture on YouTube: Ocean Deposits - Learning with 3 Classifications & Mnemonics

Ocean Deposits - Learning with 3 Classifications & Mnemonics

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Slow sedimentation where eroded particles slowly filter through oceanic water and settle in layers

  • Muds: Terrigenous deposits from land deposited on continental shelf – blue, green or red mud depending on chemical content

  • Oozes: Pelagic deposits form oceans – shelly and skeletal remains of marine microorganisms with calcium or silica – have fine flour like texture

  • Clays: Mainly as red clay in deeper oceans due to accumulation of volcanic dust


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Watch Video Lecture on YouTube: Thermohaline Circulation & Ocean Salinity Made Simple

Thermohaline Circulation & Ocean Salinity Made Simple

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Image of Ocean Salinity

Image of Ocean Salinity

  • NaCl or common salt form 77%

  • Other salts include magnesium, calcium, potassium

  • Due to free movement, salts remain remarkably constant in all oceans and even at great depths – but degree of concentration varies – expressed as salinity (degree of saltness in water)

  • Isohalines – lines joining places of equal degree of salinity

  • Average salinity is 35.2 parts per thousand

  • Baltic Sea (dilution of fresh water) – salinity is 7 parts per thousand

  • Red Sea – much surface evaporation and fewer rivers – salinity is 39 parts per thousand

  • Caspian Sea – enclosed sea with salinity at 180 & for Dead Sea it is around 250. Highest for Lake Van (Asia Minor) at 330. With high density in Lake Van and Dead Sea it is impossible to sink (beginner swimmers find it easier to float)

  • Salinity is affected by:

  • Rate of evaporation: High pressure belts of trade wind desert between – High salinity caused by high temperature and low humidity. Temperate oceans have low salinity due to lower evaporation & temperature

  • Fresh water is added by precipitation, streams and icebergs – salinity is low in equatorial region due to heavy rainfall and high relative humidity. Baltic, Arctic and Antarctic waters have low salinity due to colder climate and little evaporation – as water is added by melting of icebergs & rivers (Ob, Lena, Yenisey and Mackenzie)

  • Degree of water mixing by currents: Water does not mix freely with ocean waters in enclosed seas and salinity is high – current freely flows and salinity is at 35 parts per thousand or lower & free mixing of water

Temperature of Oceans

Image of Temperature of Oceans

Image of Temperature of Oceans

  • Annual range of temperature is much smaller – less than for open seas. Mena annual temperature decreases from in equatorial region to at , reaching to freezing point at poles.

  • Cold current as Labrador current reduces surface water temperature. Warm current like North Atlantic Drift raises the temperature – making Norwegian coast ice free year round

  • Highest water temperature are seen in tropics – Red Sea with .

  • Warmer waters – Parts of ice that breaks off as icebergs and lower surface temperature of surrounding ice free seas

  • Temperature varies vertically and decreases for first 200 fathoms at rate of for every 100 fathoms. In Ocean deep below 2000 fathoms, water is uniformly cold.

  • 80% ocean waters have temperature to

Image of Changes In Ocean Water Salinity with Depth In The S …

Image of Changes in Ocean Water Salinity with Depth in the S …

Image of Temprature Process

Image of Temprature Process

Image of Surface Salinity Variatio By Latitude

Image of Surface Salinity Variatio by Latitude

Image of horizontal distribution of ocean temperature

Image of Horizontal Distribution of Ocean Temperature

Movements of Ocean Currents

Circulate in regular pattern. Warm current flow from equatorial region to poles.

Cold Currents flow from Polar Regions equatorwards and have low surface temperature

Underlying factors

  • Planetary Winds: Trade winds which move equatorial waters polewards and westwards and warm eastern coast of continents. Florida current & Gulf Stream Drift to warm southern and eastern coast of USA. South Equatorial Current warms eastern coast of Brazil as warm Brazilian current. Planetary winds have dominant influence on flow of ocean currents – strongest evidence of prevailing winds on current flow is seen in North Indian Ocean

  • Westerlies in temperate are less reliable than trade Winds – result in north-easterly flow of water in north hemisphere, so Gulf Stream is driven to Western Europe.

  • Temperature: warm water are lighter and rises while cold water is denser and sinks

  • Salinity: Water of high salinity are denser & water of low salinity flow on surface of waters of high salinity. Less Saline water of Atlantic flows into Mediterranean

  • Earth’s Rotation: It deflects freely moving objects including ocean currents to right. In north hemisphere it is clockwise (Gulf Stream and Canaries Current) while in south hemisphere it is anti-clockwise (Brazilian current and West Wind drift)

  • Land: tip of south Chile diverts West wind Drift northward as Peruvian current. Shoulder of Brazil at Cape Sao Roque divides west flowing equatorial current into Cayenne current which flows north westwards and Brazilian Current which flows south – westwards

Image of Movements of Ocean Currents

Image of Movements of Ocean Currents

Circulation of Atlantic Ocean

  • Cayenne current is joined by North Equatorial Current and heads northwest as large mass of equatorial water into Caribbean Sea

  • Part of it enters Mexico as Florida current & rest joins Gulf Stream (strongest ocean current – 35 to 100 miles wide and 2000feet deep with velocity of 3 miles an hour) off SE USA

  • At Cape Hatteras deflects eastwards due to Westerlies and rotation of earth and reaches Europe as North Atlantic Drift & diverts in to 3 currents – mainly cool Canaries current (merge with North Equatorial Current completing clockwise circuit)

  • Mid-Atlantic has no perceptible current – large amount of floating seaweed gather as Sargasso Sea

  • Irminger Current or East Greenland Current flow between Iceland and Greenland and cool North Atlantic Drift

  • Labrador Current between Greenland and Baffin Island to meet warm Gulf Stream off Newfoundland

  • South Atlantic Ocean – Circulation is anti-clockwise & collection of sea weed in mid-Atlantic is not distinctive

  • Brazilian current – deep blue waters are distinguished from muddy waters

  • Benguela Current (cold current) brings water of West Wind Drift into tropical latitudes

Circulation of Pacific Ocean

  • Greater size than Atlantic Ocean & more open nature

  • Due to greater expanse and absence of obstruction volume of water is much greater than Atlantic Equatorial current.

  • Blows as Kurushiwo or Japan current (warm current) – warm water is carried poleward as North Pacific Drift – keeping the port of Alaska ice-free

  • Cold Bering Current or Alaska Current flows southwards & is joined by Okhotsk current to meet Japan current as Oyashio, off Hokkaido.

  • Part of it drifts eastward as cool Californian current along western USA

  • South Pacific system is same as South Atlantic.

  • Chilean and Peruvian coasts are practically rainless – region is rich in microscopic marine plants and animals that attract fishes – millions of seabirds gather and droppings form guano (source of fertilizer)

Indian Ocean Circulation

  • Equatorial current pass Madagascar as Agulhas or Mozambique current which merge with West Wind Drift flowing eastwards

  • In North there is complete reversal of current direction between summer and winter due to monsoon winds

  • In Summer (June to October) – dominant wind is SW Monsoon and currents blow from southwesterly direction.

  • In Winter – NE Monsoon blows the current as NE Monsoon Drift

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