Ocean Circulation Surface circulation Deep ocean circulation Surface

Ocean Circulation Surface circulation Deep ocean circulation

Surface currents n General pattern n Gyres created by wind and modified by Coriolis effect n n Water moves horizontally Selected other currents

Trade Winds (grey) and Westerlies (green) create gyres (purple)

Gyres n n General circular flow of surface currents Western boundary currents (intensified) Eastern boundary currents Equatorial currents

Ekman transport n n Driven by winds Modified by Coriolis n Currents veer 90 degrees to the right or left of the wind (depending on hemisphere) n Water piles up in center of gyres

Ekman transport – note direction of wind over water and direction of net transport of top 100 meters of water

Ekman transport (version 2) - note arrows spiraling down – progressively smaller and changing direction down to 100 meters depth

Geostrophic circulation n Driven by gravity Modified by Coriolis effect Water flows down away from center of hill in center of gyre, but bends due to Coriolis

Geostrophic circulation imagine hill of water at center of gyre

Upwelling and downwelling along a coast

El Nino circulation – note position of warm and cold surface water Top – “normal” Middle – El Nino Bottom – La Nina

Deep ocean circulation n n THERMOHALINE (temp and salinity) Density driven Formation of distinct water masses Sinking at poles and movement toward equator Different from surface ocean circulation

Deep ocean circulation - simplified

Conveyor belt model of deep ocean circulation

Closer look at Gulf Stream n n Flows like a river with meanders Meanders pinch off and become rings n n Warm core eddies Cold core eddies