2 Last class we learned about ocean layers What are the three main ocean layers?How does temperature change with depth in the thermocline?How does it change below the thermocline?Teacher’s Notes:Three main layers are surface (mixed) layer, thermocline, deep oceanIn the thermocline, temperature changes rapidly with depthBelow the thermocline, temperature is relatively constant
3 Today we’re going to explore ocean currents An ocean current is a regular movement of large amounts of water along defined paths.There are two primary types of ocean currents:Surface Currents (to a depth of about 400 m)Driving factor: WindDeep Currents (entirely below the effect of wind)Driving factor: Density differencesThermohaline circulation: Ocean circulation driven by differences in density caused by temperature (“thermo”) and salinity (“haline”) variationsDeep-ocean currents are driven by differences in the water’s density, which is controlled by temperature (thermo) and salinity (haline). This process is known as thermohaline circulation.
4 Why are currents so important? Photo: NOAAInfluence world climate and weatherOcean navigation and transportationSupport marine life (transport mechanism, food source)Transport of materials (both helpful and harmful) and energy to different regions and depths of the oceanTeacher’s Note: Below are additional examples of currents supporting marine life:-The eel uses the Gulf Stream to get to the Sargasso Sea where spawning occurs.-Upwelling off the coast of Peru supports one of the most productive fishing areas in the world – nutrients brought to the surface attract large populations of anchovy.Photo:Accessed: November 2010Marine organisms like the Southernright whale (above) depend upon currentsto circulate the nutrients that supporttheir food sources
5 An important ‘current’ event: Thermohaline Circulation (THC) THC creates a world wide current system called the “global conveyor belt"The global conveyor belt begins with sinking of cold, dense water near the North Pole in North AtlanticCold temps + Sea ice = cold, salty, dense water that sinksThen water moves south and circulates around Antarctica, where cold salty conditions “recharge” itThe water then moves northward to the Indian, Pacific and Atlantic ocean basinsIt can take around 1,000 years for water to complete one cycle of the entire global conveyor belt!Teacher’s Note:Sea ice formation increases salinity because, the salt is left behind in the water as the sea ice forms.As the cold, salty dense water sinks, surface water moves in to replace it thereby starting a current.When water reaches Antarctica, the cold, salty conditions lead to more sinking, thus “recharging the current”.
6 A map of the global conveyor belt Photo: NASAPhoto:Accessed: November 2010
7 What drives ocean currents? Density gradients (differences) drive deep ocean currentsUpwelling brings cold, nutrient-rich water from the depths up to the surfaceWind is one of the primary drivers of surface currents
8 Student activityIn today’s activity, we will play a game to learn the names and locations of the ocean’s currents