NR 150 1st Edition Lecture 10 Outline of Last Lecture I Surface currents are driven by wind Outline of Current Lecture II Mass flow of ocean water is driven by wind and gravity III Surface currents flow around the periphery of ocean basins IV Seawater flows in six great surface circuits V Gyres with and without the Coriolis effect VI Westward intensification VII The center of the gyres Current Lecture I Mass flow of ocean water is driven by wind and gravity a Surface currents wind driven movements of water at or near the ocean s surface i About 10 of the ocean water is involved in surface currents ii Water is flowing horizontally in the uppermost 400 meters iii Occurs above the pycnocline b Thermohaline currents the slow deep currents that affect the vast bulk of seawater beneath the pycnocline c Surface and thermohaline circulation affect i Temperature ii Climate 1 Locations with the same latitude often experience different climates as a result of surface ocean currents iii Biological productivity d Gyres circuit of mid latitude currents around the periphery of an ocean basin These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i Gyres in balance between the pressure gradient and the Coriolis effect are called geostrophic gyres 1 Currents in these gyres are called geostrophic currents II Surface currents flow around the periphery of ocean basins a The Coriolis effect shifts currents to the right of the wind direction in the Northern Hemisphere b The Ekman spiral and Ekman transport explain the net movement of water in surface currents i Ekman spiral the top most layer of water is driven about 45 to the right left in the Northern Southern hemispheres of the wind direction 1 The water a layer deeper moves at an angle to the right left of the overlaying water respectively a This occurs with each layer deeper in the water and each layer moves slower than the one above due to friction ii Ekman transport the net motion of water down to about 100 meters after summing the effects of the Ekman spiral 1 90 to the right of the wind direction in the Northern Hemisphere 90 to the left in the Southern Hemisphere III Seawater flows in six great surface circuits a Geostrophic gyres are largely independent of one another in each hemisphere i North Atlantic gyre South Atlantic gyre North Pacific gyre South Pacific gyre Indian Ocean gyre ii West Wind Drift Antarctic Circumpolar Current not technically a gyre flows endlessly eastward around Antarctica driven by strong westerly winds and never deflected by a continent b There are 2 great currents in the Northern Hemisphere and 4 in the Southern Hemisphere i Four currents that make up a gyre two boundary currents Eastern and Western two transverse currents IV Gyres with and without the Coriolis effect a Without the Coriolis effect the ocean gyres would be perfect concentric shapes b With the Coriolis effect the shape is deflected and stretched in the direction of the winds V Westward intensification a Western boundary currents are narrow deep warm and strong currents with a steep slope i Faster and occasionally form eddies ii The Gulf Stream largest of the western boundary currents flow is 300x the flow of the Amazon b Eastern boundary currents are broad shallow cold and weak currents with a gentle slope i Transports cold water towards the equator have poorly defined boundaries ii Usually don t form eddies VI The center of the gyres a Garbage patches form from debris consisting of small plastic particles suspended at or below the surface making it impossible to detect by aircraft or satellite b The estimated size of the North Pacific garbage patch is 1 2 times the size of the United States c The garbage is 20 from ships and 80 from land