Ocean Circulation 21-23

Ocean Circulation 21-23 - Ocean Circulation Read Chapters...

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Ocean Circulation Read Chapters 8-9! Why do we care??? Transport heat from tropics to poles Influence weather, climate, and commerce Distribute nutrients and scatter organisms Gulf Stream sea surface temperatures (off the east coast of the US) as measured by satellite. Courtesy of NASA.
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Two major types of circulation Wind-driven circulation (~ 10%) surface currents Wind-driven circulation influenced by the Coriolis effect and gravity confined to upper part of the ocean (top 400- 1000m) circulation occurs in "gyres" that are confined to individual ocean basins fast (up to 2 meters per second) Thermohaline (density-driven) circulation
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Large-scale winds set up large-scale ocean currents called gyres Flow is to the right of the wind in the northern hemisphere and to the left of the wind in the southern hemisphere Gyre
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Surface Circulation Major clockwise gyres in the North Atlantic and North Pacific. Major counterclockwise gyres in the southern parts of the Atlantic, Pacific, and Indian Oceans.
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Surface Circulation Note that the current direction is not 90° to the wind direction.
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Ekman Spirals and Transportation Can carry this argument for each successive “layer” in the water column.
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Ekman Spirals and Transportation
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Surface Circulation
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And The Result Of That Transportation? Where the pressure gradient force is equal and opposite to the Coriolis force we (again) have geostrophic flow .
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Seibold & Berger Figure 4-14 (after Munk, 1955) 11 Modeled effect of winds on surface currents Most of Earth’s surface wind energy is concentrated in the easterlies (trades) and westerlies.
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Geostrophic flow Ekman transport piles up water within subtropical gyres Surface water flows downhill (gravity) and Also to the right (Coriolis effect) Balance of downhill and to the right causes geostrophic flow around the “hill”
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How does the “hill” effect the currents?
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Type of Current Features Speed Transport Western boundary narrow (<100 km) fast large (50 Sv) Currents (WBC) deep (to 2 km) toward poles warm Eastern boundary broad (~1000 km) slow small (10-15 Sv) currents (EBC) shallow (<500m) toward equator cold
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from Garrison, "Oceanography" 16 Geostrophic 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.
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This is the only place in the modern ocean where the wind-driven circulation circumnavigates the globe (is not interrupted by continents) - this is the case for both the mid- latitude westerlies and the polar easterlies Southern Ocean surface circulation
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