Presentation on theme: "Oceanic Circulation Current = a moving mass of water"— Presentation transcript:
1 Oceanic Circulation Current = a moving mass of water OCEAN WATER MOVES IN CURRENTS CAUSED BY WIND AND DIFFERENCE IN WATER DENSITY (beneath surface zone)
2 Oceanic Circulation Surface Currents horizontally flowing water in the uppermost 400m of the ocean10% of water in Oceans moves this waydriven by thermal expansion & contraction and WIND friction
3 Oceanic Circulation Surface Currents Thermohaline Circulation horizontally flowing water in the uppermost 400m of the oceandriven by thermal expansion & contraction and wind frictionThermohaline Circulationslower, deeper circulation
4 Oceanic Circulation Surface Currents Thermohaline Circulation horizontally flowing water in the uppermost 400m of the ocean (above pycnocline)driven by thermal expansion & contraction and wind frictionThermohaline Circulationslower, deeper circulation (below pycnocline)due to the action of gravity on water masses of different densities
6 “Thermocline” (refresher) Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from cold, dense deep water by a thermocline.The thermocline is a layer in which water temperature and density change rapidly.Temperate regions have a seasonal thermocline and polar regions have none.
8 Surface Currents Solar heating water expands at equator and contracts near poles
9 Surface Currents Solar heating water expands at equator and contracts near poleswater moves toward poles due to gravity
10 Surface Currents Solar heating water expands at equator and contracts near poleswater moves toward poles due to gravitywater lags behind earth’s rotation & piles up on west sides of oceans
11 Surface Currents Wind Friction drags water along Coriolis effect primary force responsible for surface currentsFriction drags water alongCoriolis effectThe “piled up” water will move in direction the wind is blowing it UNTIL the coreolis determines final direction (right of wind direction in N. Hemisphere)
12 Surface CurrentsContinents prevent continuos flow and deflect water…
13 Surface Currents Continents prevent continuous flow and deflect water… Gyrethe circular flow around the periphery of an ocean basin
14 Trade Winds = Easterlies Winds are Driven by Uneven Solar Heating and the earthsspinFig 8-1, g
15 Surface Winds, Sun’s heat, Coreolis Effect and Gravity = surface current=gyresFig 8-2, g
17 Six great current circuits North Atlantic GyreSouth Atlantic GyreNorth Pacific GyreSouth Pacific GyreWest Wind drift or Antarctic Circumpolar Current
18 Sea Surface Temperatures Insolation and ocean-surface water temperature vary with the season.Ocean temperature is highest in the tropics (25oC) and decreases poleward.Figure 5-9a Sea-Surface Temperature in AugustUsing Thermocline Principles
20 Flow within Gyres Western Boundary Currents (ex: Gulf Stream) narrow, fast, deep currents that carry warm water toward poles
21 Flow within Gyres Western Boundary Currents (ex: Gulf Stream) narrow, fast, deep currents that carry warm water toward poleswestward intensification - more concentrated due to water piling up due to eastward rotation of earth
57 5 Common Water Masses Surface water Central water Intermediate Water to 200mCentral waterto bottom of thermoclineIntermediate Waterto 1500mDeep waterbelow intermediate but not in contact with bottomBottom waterin contact with bottom
58 Some Water Masses in the Deep Atlantic Antarctic Bottom WaterNorth Atlantic Deep waterMediterranean Intermediate WaterAntarctic Intermediate Water
61 The water sinks to a density-appropriate level and then slowly flows equatorward across the basin. Deep water gradually mixes with other water masses and eventually rises to the surface.
62 Figure 8.20: The global pattern of deep circulation resembles a vast “conveyor belt” that carries surface water to the depths and back again. Begin with the formation of North Atlantic Deep Water north of Iceland. This water mass flows south through the Atlantic, then flows over (and mixes with) deep water formed near Antarctica. The combined mass circumnavigates Antarctica and then moves north into the Indian and Pacific Ocean basins. Diffuse upwelling in all of the ocean returns some of this water to the surface. Water in the conveyor gradually warms and mixes upward to be returned to the North Atlantic by surface circulation. The whole slow-moving system is important in transporting water and heat.Fig. 8-23, p. 190
63 Figure 8.24A simplified view of thermohaline circulation in the Atlantic. Surface water becomes dense and sinks in the north and south polar regions. Being denser, Antarctic Bottom Water slips beneath North Atlantic Deep Water. The water then gradually rises across a very large area in the tropical and temperate zones, then flows poleward to repeat the cycle. As noted in the text, fresh water arriving in the North Atlantic from rapidly melting polar ice could slow the formation of North Atlantic Deep Water with profound implications for the climate of Europe.Fig. 8-24, g
64 Thermohaline Circulation Sinking of water masses is offset by slow, gradual rising across warmer temperate and tropical zones
65 Thermohaline Circulation Much slower than surface circulationhundreds of years (1500?) vs 1 year (North Atlantic Gyre)
66 Remember…From lecture #1 of the course – those 1st “facts” are extremely importantLet’s review…
67 Important Facts81% of the Southern Hemisphere is covered by Ocean (remember that! It’ll become really important later…); while only 61% of the Northern Hemisphere is covered – WHY?The Oceans are 4X as deep as the Continents are high (average depth = 2.5 miles).The Pacific (Ocean) is so huge that it covers almost ½ of the Earth’s surface; it is also the Earth’s largest collection of water.We have 100X more “aquatic” habitats available on earth than terrestrial habitats (1.4 billion cubic kilometers).
71 ENSO eventsSurface winds generally move from East to West in Tropical (equator) Pacific but every 3-8 yrs. these pressure areas (typically high to low) change and you get a reversal of wind direction/atmospheric pressure (low to high) = southern oscillationEl nino = water flow name (+ southern osc. = ENSO event)Still no one really knows why/how this occurs
72 El Nino“Current of the Christ Child” because Peru had an (unexpected) abundance of fishing 1 X-Mas.
73 Why 2 names?Southern oscillation (ENSO): Weather related name (pressure changes in wind patterns are clearly associated; these drive water change)El Nino: oceanographic name (associated w/ water and temp. patterns that change biological species’ productivity in the Pacific)
74 Upwelling of cold water A non el nino yearThermocline risesUpwelling of cold waterFig 8-16a, g
75 What happens (non El Nino)? Warmest part of the Worlds’ ocean = western Pacific b/c warm water moves East to West and builds up thereAs a result you get a decreased thermocline (lower in water column, less upwelling)
76 Figure 8.21Surface temperatures for southern California in January of the normal year of 1982 (left) and in the same month of an El Niño year (1983, right).Fig. 8-21, g
78 What happens (El Nino)?Warm water (that usually moves East to West) shifts to West –> East movementSlows trade winds (southern oscillation)Pressure system shiftsWarm water on other side, less where expectedAs a result you get an increased thermocline (higher in water column, more upwelling)
79 Figure 8.22El Niño changes atmospheric circulation and weather patterns.(a) During an El Niño, low atmospheric pressure south of Alaska allows storms to move unimpeded to the Pacific coast of North America. The resulting weather is wet and cool to the south, and warm and dry in the north.Fig. 8-22a, g
81 El nino yearEastwardMovement ofWater, noupwellingFig 8-16c, g
82 The opposite – La Nina “The Girl” When we “return to normal,” it is fast w/ a huge change and increased currents, increased upwelling (thus increased cold water upwards) result.Trade winds renewed
83 Figure 8.22El Niño changes atmospheric circulation and weather patterns.(b) In La Niña years, high atmospheric pressure south of Alaska blocks the storm track. Winds veer north, lose their warmth over Canada, and sweep down as cold blasts. The Pacific Northwest gets its usual rain, but the southwest suffers drought.Fig. 8-22b, g
85 North Pole South Pole North Pole South Pole North Pole South Pole 0°North PoleSouth Pole60°W0°North PoleSouth Pole60°N30°N30°S0°60°WNorth PoleSouth Pole30°E30°WPrime meridienLatitudeLongitudeEquatorBox 2.1: Latitude and Longitude.(a) Latitude is measured as the angle between a line from Earth’s center to the equator and a line from Earth’s center to the measurement point. (b) Longitude is measured as the angle between a line from Earth’s center to the measurement point and a line from Earth’s center to the prime (or Greenwich) meridian, which is a line drawn from the North Pole to the South Pole passing through Greenwich, England. (c) Lines of latitude are always the same distance apart, but the distance between two lines of longitude varies with latitude.Stepped Art
Your consent to our cookies if you continue to use this website.