Currents Ocean Circulation Wind Patterns The westerlies and

Currents Ocean Circulation Wind Patterns The westerlies and the trade winds are two of the winds that drive the ocean’s surface currents. 12/28/2021 2

Currents Ocean water circulates in currents. Surface currents are caused mainly by wind, and affect the uppermost 10% of the ocean. Circulation of the other 90% of the ocean is driven by gravity, as Density dense water sinks and less dense water rises. Upwelling and downwelling describe the vertical movement of water masses. The Coriolis effect modifies the course of ocean currents. 12/28/2021 3

Current Notes Currents are rivers of water on or below surface Cause of currents 1. Winds create surface currents ( Trades +Westerlies) 2. Rotation of Earth ( Coriolis Effect) makes Gyres 3. Density changes causes movement More dense water moves to bottom More dense water moves less dense water Evaporation changes density Freezing changes density 12/28/2021 4

Ocean Currents What are some effects of ocean currents? Ocean currents: transfer heat from tropical to polar regions influence weather and climate distribute nutrients and scatter organisms 12/28/2021 5

Surface Currents Surface 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, solar energy, and solar winds, water often moves in a circular pattern called a gyre. 12/28/2021 6

GYRE MOVEMENT A Gyre is formed of three ocean currents. Water moves clockwise in the Northern Hemisphere gyres Counterclockwise in the Southern Hemisphere gyres. 12/28/2021 Surface Currents 7

Flow Within a Gyres can be further subdivided into distinct currents. The four interconnected currents in the North Atlantic Gyre have different flow characteristics and temperatures. 12/28/2021 8

Flow Within a Gyre The energy of the wind especially the Trade winds and the Prevailing Westerlies is transferred to the ocean to create a current at a 45 degree angle to the wind. This energy continues to 100 m where the angle is 90 degrees. This is termed the Ekman spiral. 12/28/2021 9

Geostrophic Gyres Geostropic Gyre Flow Warm currents indicated by red Cool currents indicated by blue 12/28/2021 10

Currents Within Gyres What currents are found within gyres? Western boundary currents -These are warm, narrow, deep, fast currents found at the western boundaries of ocean basins. the Gulf Stream the Kuroshio (Japan) Current the Brazil Current the Agulhas Current the Eastern Australian Current 12/28/2021 11

Currents Within Gyres What currents are found within gyres? Eastern 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 Current 12/28/2021 12

Effects of Surface Currents on Climate Currents and Climate Surface currents distribute tropical heat. The warm ocean currents are shown in red and cold currents in blue. 12/28/2021 13

Subsurface currents Thermohaline changes cause subsurface currents Ocean is high heat reservoir ( convection movement) High latitude water is more dense and it sinks Most movement is horizontal Middle of ocean ( 18 %) layering, surface is 2 % Pycnocline Density Halocline Salinity Thermocline Temperature Bottom ocean water formation makes up 80 % At the Weddell Sea in Antarctica Polar regions are highly saline Bottom water moves incredibly slow due to intense pressure 12/28/2021 14

Upwelling And Downwelling Upwelling is the upward motion of bottom water. Winds from shore blow surface waters out to sea. This motion brings cold, nutrient rich bottom water towards the surface to replace water blown out to sea. Downwelling is downward motion of water. Winds blow from the sea inland causing an abundance of water at the shore. It supplies the deeper ocean with dissolved gases. 12/28/2021 15

El Niño An El Niño Year A Non-El Niño Year In an El Niño year, the trade winds diminish and reverse. Storms over land may increase in these years. 12/28/2021 16

The Temperature-Salinity Diagram A general temperature-salinity (T-S) diagram. 12/28/2021 17

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