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Chapter 16 The Dynamic Ocean 16.1 Ocean Circulation Surface Circulation ▶ Ocean currents are masses of ocean water that flow from one place to another ▶ Surface currents – movements of water that flow horizontally in the upper part of the ocean’s surface ▶ Develop from friction btw the ocean and the wind that blows across its surface Surface Circulation ▶ Oceanographers ID currents by: ▶ 1. studying physical characteristics ▶ 2. studying chemical characteristics ▶ 3. mapping the paths of debris Surface Circulation ▶ Surface currents are controlled by 3 factors: ▶ 1. air currents (aka wind) ▶ 2. Earth’s rotation (aka Coriolis Effect) ▶ 3. shape of ocean basins Surface Circulation ▶ Winds are caused by uneven heating of the atmosphere ▶ Variations in air temp lead to variations in air density and pressure ▶ Wind has KE that is transferred to the surface of the ocean Surface Circulation The Antarctic Circumpolar Current (aka West Wind Drift) is the largest current in the world. No continents interrupt the movement of this current Gyres ▶ Huge circular moving current systems dominate the surfaces of the oceans ▶ 5 Main ocean Gyres ▶ N. Pacific Gyre ▶ S. Pacific Gyre ▶ N. Atlantic Gyre ▶ S. Atlantic Gyre ▶ Indian Ocean Gyre ▶ Coriolis effect – deflection of currents away from their original course as a result of Earth’s rotation ▶ Due to Earth’s rotation, currents are deflected to the right in the N. Hemisphere & to the left in the S. Hemisphere ▶ Wind belts AND Coriolis Effect cause GYRES Ocean Currents & Climate ▶ When currents from low latitude (near equator) regions move into high latitude (near poles), they transfer heat from warmer to cooler areas on Earth ▶ As cold water currents travel toward the equator, they help moderate the warm temperatures of adjacent land areas ▶ Play a big role in maintaining Earth’s heat balance Ocean Currents & Climate See fig 3 pg. 450 Upwelling ▶ Rising of cold water from deeper layers to replace warmer surface water ▶ Wind-induced vertical movement ▶ Brings greater concentrations of dissolved nutrients to the ocean surfaces Deep – Ocean Circulation ▶ Density currents – vertical currents of ocean H2O that results from density differences in the H20 masses ▶ Flow much more slowly than surface currents ▶ Seawater density if affected by salinity and temperature differences Deep – Ocean Circulation ▶ Most water involved in deep-ocean currents begins in high latitudes (near poles) at the surface ▶ Density currents can also result from increased salinity of ocean water due to evaporation A Conveyor Belt ▶ In a simplified model, ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean through the Indian and Pacific Oceans and back again A Conveyor Belt https://www.youtube.com/watch?v=L9zjmC8InKA A Conveyor Belt Warm H20 flows toward poles Cold, deep water upwells Density increases Temperature drops & salinity increases Dense H20 moves toward equator The cycle repeats Upwelled H20 warms