Ocean Currents that Redistribute Heat Globally

Transcription

1 Ocean Currents that Redistribute Heat Globally

2 Ocean Circulation Ocean Currents Fig. CO7

3 OCEAN CURRENTS

4 Surface ocean currents are similar to wind patterns: 1. Driven by Coriolis forces 2. Driven by winds Coriolis Effect Warm currents solid, Cold currents - dashed

5 Ocean Currents Ocean currents are driven by a combination of temperature, gravity, prevailing winds, the Coriolis effect, and the locations of continents. Warm water, like warm air, expands and rises.

6 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

7 Types of Ocean Currents Surface currents Wind-driven Primarily horizontal motion Driven by the circulation of wind above surface waters Transfer heat from warmer to cooler areas Similar to pattern of major wind belts Affect coastal climates Deep currents Driven by differences in density caused by differences in temperature and salinity Vertical and horizontal motions Provide oxygen to deep sea

8 Deep ocean currents are driven by cooling, freezing of pole-bound water (thermohaline circulation). - Deepwater formation occurs at high latitudes (near Greenland and Antarctic) - Upwelling at lower latitudes, western continental margins due to Coriolis effect. Ocean currents move 40% of excess heat from equator to poles (60% of heat transport is carried by atmosphere through storms that move along pressure gradients).

9 Deep ocean currents Cold, oxygen-rich surface water to deep ocean Dissolved O 2 important for life and mineral processes Changes in thermohaline circulation can cause global climate change Example, warmer surface waters less dense, not sink, less oxygen deep ocean

10 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

11 Gyres Gyres - the large-scale patterns of water circulation. The ocean surface currents rotate in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere.

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14 On either side of the equator, in all ocean basins, there are two west flowing currents: the North and South Equatorial.

15 The Equatorial Counter Current, which flows towards the east, is a partial return of water carried westward by the North and South Equatorial currents. In El Nino years, this current intensifies in the Pacific Ocean.

16 Flowing from the equator to high latitudes are the western boundary currents. 5 Major Locations These warm water currents have specific names associated with their location: North Atlantic - Gulf Stream (clockwise) North Pacific Kuroshio (clockwise) South Atlantic Brazil (counterclockwise) South Pacific - East Australia (counterclockwise) Indian Ocean Agulhas (counterclockwise)

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19 Ocean Currents and Climate Fig. 7.9

20 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

21 Upwelling Upwelling - as the surface currents separate from one another, deeper waters rise and replace the water that has moved away. This upward movement of water brings nutrients from the ocean bottom that supports the large populations of producers, which in turn support large populations of fish

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23 Downwelling Surface seawater moves towards an area Surface seawater piles up Seawater moves downward

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25 Thermohaline circulation Thermohaline circulation - another oceanic circulation that drives the mixing of surface water and deep water. Scientists believe this process is crucial for moving heat and nutrients around the globe. Thermohaline circulation appears to be driven by surface waters that contain unusually large amounts of salt.

26 Movement caused by differences in density (temperature and salinity) Cooler seawater denser Saltier seawater denser The Thermohaline Effect

27 Thermohaline Circulation Some of the water that flows from the Gulf of Mexico to the North Atlantic freezes or evaporates, and the salt that remains behind increases the salt concentration of the water. This cold, salty water is relatively dense, so it sinks to the bottom of the ocean, mixing with deeper ocean waters. These two processes create the movement necessary to drive a deep, cold current that slowly moves past Antarctica and northward to the northern Pacific Ocean.

28 Heat Transport Ocean currents can affect the temperature of nearby landmasses. For example, England's average winter temperature is approximately 20 C (36 F) warmer than Newfoundland, Canada, which is located at a similar latitude.

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30 Climate effects of North Atlantic currents Gulf Stream Current warms East coast of U.S. and Northern Europe North Atlantic and Norwegian Currents warm northwestern Europe Labrador Current cools eastern Canada Canary Current cools North Africa coast

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32 In summer at 60 º N & S, air descends over cold ocean (high pressure) and rises over warm land (low pressure) Cool equatorward flow of air on West coast of continents Warm poleward flow of air on East coasts of continents

33 El Niño-Southern Oscillation (ENSO) El Nino and La Nina

34 Normal conditions

35 El Niño Southern Oscillation - The Pacific Ocean strongly influences the global climate system because it is the largest ocean basin - Normal ocean current and wind direction in central Pacific is easterly

36 El Niño-Southern Oscillation (ENSO) Warm (El Niño) and cold phases (La Niña) High pressure in eastern Pacific weakens Weaker trade winds Warm pool migrates eastward Thermocline deeper in eastern Pacific Downwelling

37 Atmospheric and Oceanic Disturbances in Pacific Ocean El Nino-Southern Oscillation Every 3 to 7 years, the interaction of the Earth's atmosphere and ocean cause surface currents in the tropical Pacific Ocean to reverse direction.

38 El Nino-Southern Oscillation First, the trade winds near South America weaken. This weakening allows warm equatorial water from the western Pacific to move eastward toward the west coast of South America. The movement of warm water and air toward South America suppresses upwelling off the coast of Peru and decreases productivity there, reducing fish populations near the coast. These periodic changes in wind and ocean currents are collectively called the EL Nino-Southern Oscillation, or ENSO.

39 El Niño-Southern Oscillation (ENSO): Warm phase (El Niño)

40 El Niño-Southern Oscillation (ENSO): cool phase (La Niña) Increased pressure difference across equatorial Pacific Stronger trade winds Stronger upwelling in eastern Pacific Shallower thermocline Cooler than normal seawater Higher biological productivity

41 El Niño-Southern Oscillation (ENSO) Cool phase (La Niña)

42 ENSO Events Phases usually last 12 to 18 months Fig. 7.22

43 ENSO events result from weakening of tropical Pacific atmospheric and oceanic circulation Climatic connections carry these climate effects throughout the globe (e.g., El Niño creates warm winters in AK and lots of rain in Calif) 2.19

44 These general circulation patterns are modified by the distribution of oceans and continents. High heat capacity of water and ocean currents buffer ocean temperatures Land temperatures fluctuate more, especially in higher latitudes These differences in surface energy balance influence air movements, and create prevailing winds

45 Conveyor-belt circulation Combination deep ocean currents and surface currents Fig. 7.27

46 Rain Shadows When air moving inland from the ocean that contains a large amount of water vapor meets the windward side of a mountain range (the side facing the wind), it rises and begins to experience adiabatic cooling. Because water vapor condenses as air cools, clouds form and precipitation falls.

47 The presence of the mountain range causes large amounts of precipitin to fall on its windward side. The cold, dry air then travels to the other side of the mountain range (the leeward side), where it descends and experiences higher pressures, which cause adiabatic heating. This air is now war and dry and process arid conditions on the leeward side forming the region called a rain shadow. Rain Shadows

48 STOP HERE!!!!!

49 II. Changes in climate A. Seasonal (see I.B.) B. Yearly (interannual) C. Millenial scales D. Human impacts - Is global warming for real? - How do we know that it isn t just a natural fluctuation in temperature? - What are some of the forces that lead to natural climate variability?

50 Oceans affect terrestrial climate by 1. High heat capacity of water 2. Currents 3. Upwelling 2.9

51 Core Case Study: A Temperate Deciduous Forest Why do forests grow in some areas and not others? Climate Tropical Polar Temperate Temperate deciduous forests Globally more disturbed than any other ecosystem

52 Three Major Climate Zones Fig. 7-1, p. 144

53 7-1 What Factors Influence Climate? Key factors that determine an area s climate Incoming solar energy The earth s rotation Global patterns of air and water movement Gases in the atmosphere The earth s surface features

54 The Earth Has Many Different Climates Weather Set of physical conditions of the lower atmosphere Includes temperature, precipitation, wind speed, cloud cover in a given area Over a period of hours or days Climate Sum of weather conditions in a given area, averaged over a long period of time. Area s general pattern of atmospheric conditions Ranges from over decades and to thousands of years

55 The Earth Has Many Different Climates (cont d.) Fig. 7-2, p. 145

56 The Earth Has Many Different Climates (cont d.) To determine climate, data must be collected and analyzed on the average temperature and precipitation in a given area year to year for at least three decades. Based on this analysis, scientists have described the various regions of the earth according to their climates.

57 To help determine regional climates, scientist also study: Ocean currents Mass movements of surface water driven by winds blowing over the oceans. Help to redistribute heat from the sun, influencing climate and vegetation Heat and differences in water density create warm and cold ocean currents Prevailing winds and irregularly shaped continents cause them to flow in roughly circular patterns between continents, clockwise in the northern hemisphere and counterclockwise in the southern Water also moves vertically in oceans as denser water sinks while less dense water rises; a connected loop of deep and shallow ocean currents that transports warm and cool water to various parts of the earth.

58 Climate varies among the earth s different regions primarily because patterns of global air circulation and ocean currents distribute heat and precipitation unevenly between the tropics and other parts the of the world.

59 The Earth Has Many Different Climates (cont d.) 3 major factors that affect air circulation in lower atmosphere: 1. Uneven heating of the earth s surface by sun Air is heated much more at the equator, where the sun s rays strike directly, than at the poles, where sunlight strikes at an angle and spreads out over a much greater area.

60 2. Rotation of the earth on its axis As the earth rotates around its axis, the equator spins faster than the regions to its north and south. As a result, heated air masses, rising above the equator and moving north and south to cooler areas, are deflected in different ways over different parts of the planet s surface. Divides the atmosphere into regions called cells Differing directions of air, prevailing winds, help to distribute heat and moisture over the earth s surface and drive ocean currents.

61 3. Properties of air, water, and land Heat from the sun evaporates ocean water and transfers heat from the oceans to the atmosphere, especially near the hot equator. Evaporation of water creates giant cyclical convection cells that circulate air, heat, and moisture both vertically and from place to place in the atmosphere.

62 The Earth Has Many Different Climates (cont d.) The highest solar energy input is at the equator. 30 N Polar cap Cold deserts 60 N Evergreen coniferous forest Westerlies Temperate deciduous forest and grassland Northeast trades Hot desert Moist air rises, cools, and releases moisture as rain Air cools and descends at lower latitudes. Solar energy Equator 30 S Southeast trades 60 S Westerlies Polar cap Tropical deciduous forest Tropical rain forest Tropical deciduous forest Hot desert Temperate deciduous forest and grassland Cold deserts Warm air rises and moves toward the poles. Air cools and descends at lower latitudes. Fig. 7-3, p. 146

63 The Earth Has Many Different Climates (cont d.) Warm, less salty, shallow current Cold, salty, deep current Fig. 7-5, p. 147

64 The ocean and atmosphere are strongly linked in two ways: 1. ocean currents are affected by winds in the atmosphere. 2. heat from the ocean affects atmospheric circulation. Example: El Nino-Southern Oscillation, or ENSO

65 The Earth Has Many Different Climates (cont d.) El Niño-Southern Oscillation Occurs every few years Prevailing winds in tropical Pacific Ocean change direction Affects much of earth s weather for 1-2 years

66 What is the link between air circulation, ocean currents, and biomes? Air circulation patterns, prevailing winds, and configuration of continents and oceans are all factors in the formation of six giant convection cells, 3 south of the equator and three north. Cells lead to an irregular distribution of climates and of the resulting deserts, grasslands, and forests.

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