PowerPoint PresentationSurface Currents Are Driven by the WindsSurface CurrentsSurface Currents Are Driven by the WindsSurface Currents Flow around the Periphery of Ocean BasinsSlide 6Slide 7Slide 8Seawater Flows in Six Great Surface CircuitsSlide 10Slide 11Boundary Currents Have Different CharacteristicsSurface Currents Affect Weather and ClimateSlide 14Slide 15Slide 16Thermohaline Circulation Affects All the Ocean’s WaterSlide 18Slide 19Thermohaline Circulation (THC), Surface Circulation, and Meridional Overturning Circulation (MOC, global heat connection)Water Masses May Converge, Fall, Travel across the Seabed, and Slowly RiseSlide 22Slide 23Slide 24MOC: Variability (Agulhas Leakage, Malvinas Current)Slide 26Slide 27Slide 28Slide 29Slide 30Chapter 9 Circulation of the OceanSurface Currents Are Driven by the WindsThe westerlies and the trade winds are two of the winds that drive the ocean’s surface currents.About 10% of the water in the world ocean is involved in surface currents, water flowing horizontally in the uppermost 400 meters (1,300 feet) of the ocean’s surface, driven mainly by wind friction.(left) Winds, driven by uneven solar heating and Earth’s spin, drive the movement of the ocean’s surface currents. The prime movers are the powerful westerlies and the persistent trade winds (easterlies).Surface CurrentsWhat are some effects of ocean currents?Transfer heat from tropical to polar regionsInfluence weather and climateDistribute nutrients and scatter organismsSurface currents are driven by wind:Most of Earth’s surface wind energy is concentrated in the easterlies and westerlies.Due to the forces of gravity, the Coriolis effect, and winds, water often moves in a circular pattern called a gyre.Surface Currents Are Driven by the WindsThe gyres circulate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.The North Atlantic gyre, a series of four interconnecting currents with different flow characteristics and temperatures.Surface Currents Flow around the Periphery of Ocean BasinsSurface water blown by the winds at point A will veer to the right of its initial path and continue to the east. Water at point B veers right and continues to the west.The Ekman spiral and the mechanism by which it operates. Surface Currents Flow around the Periphery of Ocean Basins90° to the right of winddirection is up hereAt 15°N30°– 45°Trade windStepped ArtFig. 9-6, p. 237Surface Currents Flow around the Periphery of Ocean BasinsThe surface is raised through wind motion and Ekman transport to form a low hill. The westward-moving water at B ‘feels’ a balanced pull from two forces: the one due to Coriolis effect (which would turn the water to the right) and the one due to the pressure gradient, driven by gravity (which would turn it to the left). The hill is formed by Ekman transport. Water turns clockwise (inward) to form the dome, then descends, depressing the thermocline.Consider the North Atlantic.Seawater Flows in Six Great Surface CircuitsGeostrophic gyres are gyres in balance between the pressure gradient and the Coriolis effect. Of the six great currents in the world’s ocean, five are geostrophic gyres. Note the western boundary currents in this map.Western boundary currents – These are narrow, deep, warm, fast currents found at the western boundaries of ocean basins.The Gulf StreamThe Japan CurrentThe Brazil CurrentThe Agulhas CurrentThe Eastern Australian CurrentEastern boundary currents – These currents are cold, shallow and broad, and their boundaries are not well defined.The Canary CurrentThe Benguela CurrentThe California CurrentThe West Australian CurrentThe Peru CurrentBoundary Currents Have Different CharacteristicsBoundary Currents Have Different CharacteristicsThe general surface circulation of the North Atlantic. Unit for measuring flow rates (or volume transported by ocean currents):sverdrups 1 sv = 1 million cubic meters of water per secondBoundary Currents Have Different CharacteristicsEddy formationThe western boundary of the Gulf Stream is usually distinct, marked by abrupt changes in water temperature, speed, and direction.(a) Meanders (eddies) form at this boundary as the Gulf Stream leaves the U.S. coast at Cape Hatteras. The meanders can pinch off (b) and eventually become isolated cells of warm water between the Gulf Stream and the coast (c). Likewise, cold cells can pinch off and become entrained in the Gulf Stream itself (d). (C = cold water, W = warm water; blue = cold, red = warm.)Surface Currents Affect Weather and ClimateGeneral summer air circulation patterns of the east and west coasts of the United States. Warm ocean currents are shown in red; cold currents, in blue. Air is chilled as it approaches the west coast and warmed as it approaches the east coast.Surface Currents Affect Weather and ClimateWind induced vertical circulation is vertical movement induced by wind-driven horizontal movement of water.Upwelling is the upward motion of water. This motion brings cold, nutrient rich water towards the surface.Downwelling is downward motion of water. It supplies the deeper ocean with dissolved gases.15Consider: West and East WindsThermohaline Circulation Affects All the Ocean’s WaterThe movement of water due to different densities is thermohaline circulation. Remember that the ocean is density stratified, with the densest water at the bottom. There are five common water masses:•Surface water = 0-200m•Central water = 200-thermocline•Intermediate water = thermocline-1500m•Deep water = 1500-4000m•Bottom water = 4000-bottom•Density Structure–Temperature increase = density decrease–Salinity increase = density increase•Density Changes–Evaporation–Sea ice formation–Melting–River influx–Precipitation Caballing = the mixing and sinking of water masses•Thermohaline Circulation–Vertical, density driven circulation, resulting from change in temperature and salinity•Continuity of flow–Water is a relatively fixed quantity in the oceans–Water can not accumulate in one location or be removed from another location without movement of water between those locations•Vertical movement of water•Horizontal movement of waterThermohaline Circulation (THC), Surface Circulation, and Meridional Overturning Circulation (MOC, global heat connection)Water Masses May Converge, Fall, Travel across the Seabed, and Slowly RiseA model of thermocline