04 Ocean Currents

04 Ocean Currents - The Dynamic Ocean Chapter 14 The...

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Unformatted text preview: The Dynamic Ocean Chapter 14 The Dynamic Ocean Surface Circulation Deep-Ocean Circulation Waves Beaches and Shoreline Processes Shoreline Features Stabilizing the Shore Coastal Classification Tides Surface Circulation Ocean currents are masses of water that flow from one place to another Surface currents develop from friction between the ocean and the wind that blows across the surface Surface currents create huge, slowly moving gyres Types of ocean currents Surface currents Wind-driven Primarily horizontal motion Deep currents Driven by differences in density caused by differences in temperature and salinity Vertical and horizontal motions Benjamin Franklin, as the first postmaster general, published the first map of the gulf stream. Measuring surface currents Measuring surface currents Direct methods Floating device tracked through time Fixed current meter Indirect methods Pressure gradients Radar altimeters Doppler flow meter Accidental drift meters may be the result of container ships that lose some of their cargo during storms 61,820 Nike shoes were lost by the Hansa Carrier in 1990. Surface currents Frictional drag between wind and ocean Wind plus other factors such as Distribution of continents Gravity Friction Coriolis effect cause Gyres or large circular loops of moving water Ocean gyres Subtropical gyres Centered about 30o N or S Equatorial current Western Boundary currents Northern or Southern Boundary currents Eastern Boundary currents Fig. 7.3 Surface Circulation Five main gyres related to atmospheric circulation North Pacific Gyre South Pacific Gyre North Atlantic Gyre South Atlantic Gyre Indian Ocean Gyre Smaller gyres in interesting places Average ocean surface currents Surface Circulation Deflected by the Coriolis effect To the right in the Northern Hemisphere To the left in the Southern Hemisphere Surface Circulation Importance of surface currents Climate Currents from low latitudes into higher latitudes (warm currents) transfer heat from warmer to cooler areas Influence of cold currents is most pronounced in the tropics or during the summer months in the middle latitudes Average ocean surface currents Ocean currents and climate Warm ocean currents warm air at coast Warm, humid air Humid climate on adjoining landmass Cool ocean currents cool air at coast Cool, dry air Dry climate on adjoining landmass Ocean currents and climate Fig. 78a Atlantic Ocean circulation South Atlantic Subtropical Gyre Brazil Current Antarctic Circumpolar Current Benguela Current South Equatorial Current Fig. 7.14 Perhaps the strongest storm in the recorded history of the South Atlantic Ocean crossed the coast of Brazil in early April 2004. Named "Caterina", this storm was classified as the first ever Category 1 Hurricane. (note the clockwise rotation) Katrina at Saffir-Simpson Level 5 Gulf Stream Best studied Meanders or loops Warm core rings Coldcore rings Fig. 7.16 Other surface currents Equatorial Countercurrents Subpolar gyres Antarctic circulation Antarctic Circumpolar Current (West Wind Drift) Encircles Earth Transports more water than any other current East Wind Drift Antarctic Divergence Antarctic Convergence Pacific Ocean circulation North Pacific subtropical gyre Kuroshio North Pacific Current California Current North Equatorial Current Alaskan Current Pacific Ocean circulation South Pacific subtropical gyre East Australian Current Antarctic Circumpolar Current Peru Current South Equatorial Current Equatorial Counter Current Atmospheric and oceanic disturbances in Pacific Ocean Normal conditions Air pressure across equatorial Pacific is higher in eastern Pacific Strong southeast trade winds Pacific warm pool on western side Thermocline deeper on western side Upwelling off the coast of Peru Normal conditions Fig. 7.18 a Atmospheric and oceanic disturbances in Pacific Ocean El Nio-Southern Oscillation (ENSO) Warm (El Nio) and cold phases (La Nia) High pressure in eastern Pacific weakens Weaker trade winds Warm pool migrates eastward Thermocline deeper in eastern Pacific Downwelling Lower biological productivity Corals particularly sensitive to warmer seawater El Nio-Southern Oscillation (ENSO): Warm phase (El Nio) Fig. 7.18 b El Nio-Southern Oscillation (ENSO): cool phase (La Nia) Increased pressure difference across equatorial Pacific Stronger trade winds Stronger upwelling in eastern Pacific Shallower thermocline Cooler than normal seawater Higher biological productivity El Nio-Southern Oscillation (ENSO) Cool phase (La Nia) Fig. 7.18c Surface Circulation Upwelling The rising of cold water from deeper layers Most characteristic along west coasts of continents Brings greater concentrations of dissolved nutrients to the ocean surface ENSO events El Nio warm phase about every 2 to 10 years Highly irregular Phases usually last 12 to 18 months ENSO events Strong conditions influence global weather, e.g. 1982-1983 El Nio Flooding, drought, erosion, fires, tropical storms, harmful effects on marine life Fig. 7.21 Atmospheric Disturbances in the Atlantic Ocean Reduced sunspot activity Unpredictable North Atlantic Oscillation Climate Extremes Crop Failures Famine and Pestilence One-third of Population Dies The Little Ice Age The Gulf Stream High North Atlantic Oscillation Gulf Stream (High) Low North Atlantic Oscillation Gulf Stream (Low) Ocean Circulation The Dynamic Ocean Surface Circulation Deep-Ocean Circulation Waves Beaches and Shoreline Processes Shoreline Features Stabilizing the Shore Coastal Classification Tides Deep-Ocean Circulation A response to density differences Factors creating a dense mass of water Temperature cold water is dense Salinity density increases with increasing salinity Called thermohaline circulation Deep-Ocean Circulation Most water involved in deep-ocean currents begins in high latitudes at the surface A simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean, through the Indian and Pacific Oceans and back again Idealized "conveyor belt" model of ocean circulation Ocean currents Moving seawater Surface ocean currents Transfer heat from warmer to cooler areas Similar to pattern of major wind belts Affect coastal climates Deep ocean currents Provide oxygen to deep sea Affect marine life Measuring deep currents Floating devices tracked through time Chemical tracers Tritium Chlorofluorocarbons Characteristic temperature and salinity ...
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This note was uploaded on 08/07/2008 for the course GEO 1408 taught by Professor Greene during the Summer '07 term at Baylor.

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