Ocean currents ,productivity,coral reefs
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Ocean currents ,productivity,coral reefs






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Ocean currents ,productivity,coral reefs Ocean currents ,productivity,coral reefs Presentation Transcript

  • The first systematic study of currents was done by Maury based on logbooks in the US Navy’s Depot of Charts and Instruments. His charts and “Physical Geography of the Sea” assisted navigators worldwide. Matthew Fontaine Maury
  • Why is Ocean Circulation Important? • Transport ~ 20% of latitudinal heat – Equator to poles • Transport nutrients and organisms • Influences weather and climate • Influences commerce
  • Surface Currents The upper 400 meters of the ocean (10%). Deep Water Currents Thermal currents (90%) Ocean Currents
  • Forces 1.Solar Heating (temp, density) 2.Winds 3.Coriolis Surface Currents
  • The primary cause of surface currents is wind. The ultimate driving force of the winds over the earth is solar energy. The equatorial regions of earth receive more solar energy per unit area than does the rest of earth. The equatorial air masses rise as a result of increased heating and eventually move poleward at higher altitudes. Consequently, low pressure belts known as the doldroms are created along the equator. ATMOSPHERIC CIRCULATION
  • In order to compensate for the rising air, air masses move toward the equator near the surface The poleward moving equatorial air gradually cools and sinks at about300 north and south latitudes(the subtropical high pressure belts known as the Horse latitudes)
  • and upon reaching the earth surface, part of it spreads poleward and some moves toward the equator. The poleward moving air meets the cool,dense polar air moving toward the equator at about 600 north and south latitudes , forming the polar front.
  • Atmospheric Circulation Hot air rises at the equator Cold air sinks at the poles LP LP HP HP
  • Atmospheric Circulation Major winds: Trades Westerlies Polar easterlies Hadley Cell HP HP LP LP
  • Trade winds- between 250 north and south latitudes. - blow from the northeast in the northern hemisphere and southeast in the southern hemisphere. Westerlies- 30 degree - 60 degree Poleward esterlies –poleward of prevailing westerlies
  • ITCZ intertropical convergence zone= doldrums Low pressure, wet climate High pressure, dry climate Low pressure, wet climate 30o 30o 60o 60o 90o 90o 0o High pressure, dry climate
  • Coriolis force , which deflect all moving objects toward the right in the northern hemisphere and to the left in the southern hemisphere
  • The Coriolis effect Is a result of Earth’s rotation Causes moving objects to follow curved paths. In Northern Hemisphere, curvature is to right •In Southern Hemisphere, curvature is to left –Changes with latitude: •No Coriolis effect at Equator •Maximum Coriolis effect at poles
  • The Coriolis effect on Earth • As Earth rotates, different latitudes travel at different speeds • The change in speed with latitude causes the Coriolis effect
  • Surface current patterns Flows in closed loops, or gyres. Most of these gyres flow in a clockwise fashion in the N.H and counterclockwise in the S.H.
  • Gyres are large circular-moving loops of water Five main gyres (one in each ocean basin): • North Pacific • South Pacific • North Atlantic • South Atlantic • Indian • Generally 4 currents in each gyre Current Gyres
  • EQUATORIAL CURRENTS The currents in the equatorial regions consist of the westward flowing NORTH and SOUTH EQUATORIAL CURRENTS, which are separated by the eastward flowing EQUATORIAL COUNTER CURRENTS.
  • WESTERN BOUNDARY CURRENTS The warm westward flowing equatorial currents are deflected poleward near the western boundaries of the oceans.These currents are knows as WESTERN BOUNDARY CURRENTS. KUROSHIO EAST AUSTRALIAN CURRENTS FLORIDA GULF STREAM BRAZIL CURRENTS AGULHAS
  • Wind-driven surface currents
  • Ekman transport Ekman transport is the overall water movement due to Ekman spiral • Ideal transport is 90º from the wind • Transport direction depends on the hemisphere
  • Ekman spiral Ekman spiral describes the speed and direction of flow of surface waters at various depths • Factors: – Wind – Coriolis effect
  • Ekman Transport Water flow in the Northern hemisphere- 90o to the right of the wind direction Depth is important
  • Upwelling and downwelling Vertical movement of water () – Upwelling = movement of deep water to surface • Cold, nutrient-rich water to surface • Produces high productivities and abundant marine life – Downwelling = movement of surface water down • Moves warm, nutrient-depleted surface water down • Not associated with high productivities or abundant marine life
  • Deeper water must move toward the surface along the coast to replace the water that has moved offshore – upwelling (From 400 meters) Cold deeper water is generally rich in nutrients,and when it is upwelled ,surface productivity is enhanced. Slow process Seasonal process(because the wind conditions near the coasts are usually variable) E.G, PERUVIAN COAST
  • upwelling downwelling
  • Along the peruvian coast ,upwelling has produced one of the world’s greatest anchovy fisheries. Occasionally, the normally strong trade winds are weakened in this area, causing a cessation of upwelling and a movement of warm, nutrient-poor, tropical water southward over the northward flowing peru current.
  • The resulting decrease in productivity causes the death of many animals. This results in anaerobic conditions and the production of hydrogen sulfide gas by anaerobic bacteria.
  • Hydrogen sulfide discolors the hulls of ships and the exteriors of homes and is sometimes referred to as the Callao painter, after a Peruvian port city The phenomenon usually occurs around Christmas, so it is also known as El Nino(“the Child”).
  • El Nino • Oceanic and atmospheric phenomenon in the Pacific Ocean • Occurs during December • 2 to 7 year cycle Sea Surface Temperature Atmospheric Winds
  • l World Wide Effects of El Niño • Weather patterns • Marine Life • Economic resources
  • Effects of severe El Niños
  • GEOSTROPHIC BALANCE Coriolis force acting on the current is balanced by an equal and opposite force .This opposing force is the pressure gradient force. One type of flow ,in which the coriolis force is exactly balanced by pressure gradient force , is called geostrophic current
  • Wind-Driven and Density-Driven Currents • Wind-driven currents occur in the uppermost 100 m or less • Density differences causes by salinity and temperature produce very slow flows in deeper waters.
  • Deep ocean currents ,involve horizontal and vertical flow extending into the deepest parts of the oceans.
  • They are the result of minute horizontal and vertical density variations in the sea. In the long run the deep circulations is inseparable from that at the surface. Even deep water is returned to the surface , becomes part of the surface currents ,and eventually sinks to rejoin the deep circulation
  • Responsible for carrying oxygen into the deepest parts of the seas, enabling marine animals to exist at all depths Returning nutrients to the surface
  • Deep ocean current - very slow (40cm/se) PATTERN - north – south (Surface currents - 50-100cm/sec)
  • Causes of deep ocean currents In order of water to sink, it must be denser than the surrounding water. Freezing of sea water into salt- free ice causes an increase in density of adjacent residual water. Evaporation(increased salinity) and cooling both the result in dense water.
  • Wind - driven surface circulation leads to transport of water toward regions where mixing and sinking are possible.
  • TIDES Tides are the periodic rise and fall of the ocean level, that occurs every 12 hours and 26 minutes. They are produced essentially due to the bulging of water by attraction of the moon and sun upon earth. On the side nearest to the moon, the attraction is stronger than the earth’s centre because gravitational force decreases with an increase in the distance separating the two masses.
  • By this attractive force the ocean water will move to the sides adjuscent and farthest from the moon in the earth. This tidal bulges affects twice daily in the earth as the earth rotates on its axis
  • Each bulge produces a rise of ocean level to a maximum, or high tide, and a lowering of water level to a minimum or low tide. The interval between an alternate high and low tide is approximately 6 hours and 25 minutes
  • The effect of the sun is similar to that of the moon but less powerful. When the earth, moon and sun fall along the same straight line, resulting tides will be of maximum range, and is known as spring tides
  • When the sun and moon are at the right angles to the earth, the moon produces high tides and sun has low tides. Resulting tides of rather less range are called neap tides In the open ocean the difference between high and low tide is only a meter or less.
  • Regularly occurring movements in the water as the result of interactions between the ocean surface and winds that blow across the water. waves
  • The energy imparted to the water produces wave motion , but the only progressive movement is of energy through the water , not the water itself. Wave motion is modified by the general Contour of the ocean basin, especially as waves approach the shoreline.
  • Wave size depends on several factors. The wind speed determines the amount of energy imparted to the water, and fetch, or distance over which the wind blows.
  • Wave size also depends on the duration of the wind. Sea waves are directly produced by wind stress on ocean surface .
  • Waves are important cause of alterations and evolution of our coastlines. As wave approaches the shore , they erode and transport material ,the manner of transport and subsequent deposition are uniquely determined by the shape of the land and the bottom topography over which the incoming wave passes
  • Primary productivity • Primary productivity is the amount of carbon (organic matter) produced by organisms – Mostly through photosynthesis •Energy source = solar radiation – Also includes chemosynthesis •Energy source = chemical reactions
  • Primary Production Global chlorophyll concentrations for Oct. 2000
  • Photosynthetic productivity
  • Annual marine primary production in the world’s oceans in relation to the area where production occurs (Longhurst et al. 1995) Most of the ocean area is very unproductive; only a small fraction is highly productive
  • Primary Producers Common Name Blue-green algae (cyanobacteria) Red algae Brown algae Green algae Coccolithophorids Dinoflagellates Diatoms Seagrass
  • Oceanic photosynthetic productivity • Controlling factors affecting photosynthetic productivity: – Availability of nutrients • Nitrates • Phosphates • Iron – Amount of sunlight • Varies daily and seasonally • Sunlight strong enough to support photosynthesis occurs only to a depth of 100 meters (euphotic zone)
  • Locations of maximum photosynthetic productivity • Coastlines – Abundant supply of nutrients from land – Water shallow enough for light to penetrate all the way to the sea floor • Upwelling areas – Cool, nutrient-rich deep water is brought to the sunlit surface
  • Water color and life in the ocean • Ocean color is influenced by: – The amount of turbidity from runoff – The amount of photosynthetic pigment, which corresponds to the amount of productivity • Yellow-green = highly productive water – Found in coastal and upwelling areas (eutrophic) • Clear indigo blue = low productivity water – Found in the tropics and open ocean (oligotrophic)
  • All the organic production of the sea is derived from the phytoplankton. These minute plants feed the zooplankton and other fish, and so through the food web till the main commercial fish are reached. Sometimes phytoplankton is dense inwater that it appears slimy, or takes on a colour related to that of organism within it. e.g. Red sea (due to increase of Trichodesmium erythraeum)
  • Red tides Blue green alga
  • diatoms dinoflagellates
  • Depth Relationship between depth, phytoplankton photosynthesis and phytoplankton respiration Phytoplankton photosynthesis Phytoplankton respiration compensation depth critical depth Phytoplankton need light, nutrients and carbon dioxide to grow (nitrates, phosphates and iron can limit primary production). Photosynthesis depends strongly on light, which declines with depth. Above the compensation depth, more carbon is fixed by photosynthesis than is lost in respiration. Below that depth (which can be as deep as 100 m or as shallow as 1-2 m) more carbon is lost than is fixed. Below the critical depth there is insufficient light for phytoplankton. From Sverdrup (1953)
  • Relative Ocean Primary Production by Province 0 100 200 300 Open Ocean Coastal Upwelling Province gC/m2 /yr
  • Productivity varies greatly in different parts of the ocean in response to the availability of nutrients and sunlight. • In the tropics and subtropics sunlight is abundant, but it generates a strong thermocline that restricts upwelling of nutrients and results in lower productivity. • High productivity locally can occur in areas of coastal upwelling, in the tropical waters between the gyres and at coral reefs. • In temperate regions productivity is distinctly seasonal. • Polar waters are nutrient-rich all year but productivity is only high in the summer when light is abundant. 10-2
  • Classification • Phylum: Cnidaria • Class: Anthozoa • Radically symmetric • Sessile animals
  • •It’s a living organism! •It is an invertebrate •2 different types: –Reef Building: Hermatypic –Solitary: Ahermatypic Coral Polyps
  • Coral Builds Reefs? • The animal portion of the reef is called a polyp • The polyp absorbs calcium carbonate out of the water • The calcium carbonate is used to build the reef
  • Coral reefs are unique among marine associations or communities in that it built up entirely by biological activity. The reefs are massive deposits of calcium carbonate that have been produced primarily by corals with minor additions from calcareous algae and other organisms that secrete calcium carbonate.
  • Where Can we Find Coral Reefs? • Coral is found all over the world: –Tropical –Temperate –Polar • Only tropical corals build reefs Coral reefs around the world
  • Biology Best grow in sunny, shallow clear water- helps coral get sunlight , which is essential in order to carry out photosynthesis  Usually don’t grow deeper than 40m and prefer salt water  Coral polyps have a symbiotic relationship with zooxanthellae  Zooxanthellae- single celled algae carry out photosynthesis in order for the coral polyp to receive nutrients  Coral gives a protective home to the algae, and in return the algae supplies the coral with oxygen and helps it to remove wastes  Zooxanthellae provides coral with organic products such as glucose, glycerol, and amino acids which are essential in producing protein, fats and carbohydrates  Cyanobacteria provide soluble nitrates for coral reefs through nitrogen fixation  Corals feed upon zooplankton Zooxanthellaewith corals
  • Types of Coral Reefs  Atoll Reef- a ring like coral enclosing only a shallow marine water  The portion of sea enclosed within atoll is lagoon.  Fringing Reef : built along the margin of main land or margin of islands  Barrier Reef- such grow as offshore barriers.The water enclosed between mainland and reef remains in contact with numerous opening in the reef barrier Example of a fringing reef
  • Importance of Coral Reefs • Home to many organisms and species of fish • Fishery and nursery area- important economically • Provides many people with income • Provide a protective barrier from erosion to coastlines • Provide information on changes in water quality (because Coral Reefs are very sensitive) • Tourist attractions • Control the amount of carbon dioxide in the water Jewelry made from coral
  • Cool Facts 1. One of the oldest ecosystems on Earth 2. Largest living structure on Earth 3. Without coral reefs, parts of Florida would be underwater 4. Have been used to treat cancer, HIV, cardiovascular diseases along with ulcers 5. Provide 375 billion dollars a year in goods and services 6. Their limestone skeletons have been used for human bone grafts 7. Protect coasts from wave erosion 8. 10% of the worlds reefs have been destroyed 9. Over 70% of the coral reefs in the Philippines have been destroyed 10. Home to 25% of all marine life 11. Coral is found in about 100 countries
  • The Destruction of Coral Reefs  Pollution- poorly managed land development  Fish Trade- over-fishing * Use of cyanide to capture fish (80- 90% of exported fish from the Philippines are caught with the use of sodium cyanide)  Dynamite Fishing- not only kills fish, but also coral  Coral Bleaching- caused by global warming- the high temperatures kills the zooxanthellae that provide the coral with nutrients  Ocean Acidification- the decrease in the ocean’s surface pH level, increases the amount of CO2 dissolved in the oceans  African and Asia dust outbreaks- the dust that blows into the oceans declines the health of the coral reefs