Ocean circulation Two types of ocean currents: • surface currents • deep ocean circulation

Surface Waters Circulate Horizontally, Pushed By Surface Winds Of Hadley, Ferrel, Polar Cells Called gyres

N W E S The Gulf Stream flows north, pushed by the trade winds of the tropics, warming the SE coast Florida Gulf Stream

N W E S The California Current flows south, pushed by the Westerlies, keeping the western Pacific ocean cool Florida Gulf Stream

Surface Currents = Gyres 5 Gyres exist • Caused by winds • 1 Cycle takes ~ 10 yrs • Turned by Continents, Coriolis

The center of gyres have become giant whirling collections of garbage • All 5 gyres • Pacific’s is huge!

Breaks into small pieces Animals ingest it 6x more plastic than plankton

Deep Water Circulation Coldest, saltiest water at Arctic sinks • A continuous deep current slowly drains one ocean into another • All the water is turned over in the process Antarctica recharges cold water

Recall: Angle of Solar Radiation Heats Earth’s Surface Unequally Sunlight Ocean currents are ultimately powered by energy from the sun, but how the oceans are affected by the sun depends on latitude. The intensity of sunlight is highest in the tropics and decreases as you go towards the poles. Here, the yellow bars represent the same amount of sunlight hitting the earth at different parts of the globe. At 60° north (click), the approximate latitude of Anchorage, Alaska, the same amount of sunlight would only have about half the intensity of sunlight as that at the equator. To think about it another way (click), if you took the sun that was hitting a square this big at the equator, it would be spread out over a square this big at 60° north. Because of differences in sunlight intensity, the average annual temperature in the Galapagos Islands on the equator is about 76°F while it is only 36°F in Anchorage, Alaska. This difference in sunlight intensity causes the oceans to heat differently. (click) Image based on: http://www.windows.ucar.edu/tour/link=/earth/climate/sun_radiation_at_earth.html&edu=mid&back=/search/search_navigation.html Modified image from Windows to the Universe, http://www.windows.ucar.edu 9

Ocean Surface Temperature is Varied as a Result 10 Radiation affects temp, density, evaporation This image shows temperatures of the ocean surface across the world. Temperature is color-coded where red colors indicate warmer temperatures, and blue and violet indicate colder temperatures. For example, the reddish area in the middle of the map shows that the oceans are warmer in the tropics. The heat absorbed in the tropics is transported north and south to higher latitudes by atmospheric and oceanic circulation. (click) Image source: http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_03.htm Cold, dense; sinking water oceanworld.tamu.edu 10

Salinity is Another Factor the amount of salt dissolved in water evaporation, freezing act to increase salinity rain, runoff, & thawing of ice decrease salinity Higher salt = greater density

Factors influencing seawater density

All these density differences creates the Great Ocean Conveyor Belt Takes 1000 years for a complete cycle

Normal El Nino http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html

Warmer than normal : El Nino Colder than normal : La Nina Oceans temps measured via buoys

El Nino affects local weather, westerlies (jet stream), fisheries